Friday, July 18, 2014

Top Clinical Endocrinology Research Abstracts, 2014 ACVIM Forum: Adrenal Part 1


Below is the next installment of my review of the "top 12 list" of clinical endocrinology research abstracts presented at this year's American College of Veterinary Internal Medicine Forum.

As with all of these ACVIM research abstract reviews, I've enlisted the help of Dr. Rhett Nichols, a well-known expert in endocrinology and internal medicine whose day-job is senior member of the veterinarian consulting service for Antech Diagnostics, the world's largest laboratory dedicated to animal health.

In this post, we will review another of these "top 12" abstracts (starting with the adrenal gland abstracts). Next week, we will finish up the top clinical abstracts dealing with the adrenal gland, and then go on to disorders of the thyroid over the next 2 weeks.


Schrage A, Appleman E, Langston C. Iatrogenic Hypoadrenocorticism Following Trilostane Therapy for Pituitary-Dependent Hyperadrenocorticism in Dogs. J Vet Intern Med 2014;28:1035.

     This retrospective case series identified 13 dogs that developed iatrogenic hypoadrenocorticism (iHAC) following administration of trilostane for treatment of pituitary-dependent hyperadrenocorticism (PDH). Inclusion criteria required a previous diagnosis of PDH, monotherapy with trilostane (i.e., no other medications used for treatment of PDH), and a post- ACTH stimulated cortisol concentration of < 1 μg/dL while receiving trilostane. 
     Clinical signs of PDH resolved in 92% (12/13) of dogs prior to development of iHAC. At the time of diagnosis, 7/13 (53%) dogs had clinical signs consistent with iHAC. Lethargy and inappetence were the most common signs. Median age of dogs was 12 years with a median weight of 10 kilograms. No single breed was overrepresented. Dogs were treated with trilostane for a median of 8.5 months at a median dosage of 4.75 mg/kg/day prior to development of iHAC. Mineralocorticoid deficiency (hyperkalemia ± hyponatremia) was identified in 3/13 (23%) dogs. Trilostane was discontinued in all 7 dogs displaying clinical signs and later restarted at a lower dose in 2 dogs. Permanent hypoadrenocorticism developed in 4 dogs. No dog died or was euthanized as a result of iHAC. 
     This report illustrates that, while trilostane is an effective treatment for PDH, transient or permanent iatrogenic hypoadrenocorticism may occur. Development of mineralocorticoid deficiency is less common in comparison to glucocorticoid deficiency. These dogs were being closely evaluated and had received manufacturer-recommended doses of trilostane prior to development of iHAC. Close monitoring of dogs on trilostane therapy is warranted, with special emphasis on clinical signs, electrolyte levels, and cortisol concentrations.

Comments— This report emphasizes that trilostane (Vetoryl) is not a benign drug. Although safer to use than mitotane, trilostane can certainly result in hypoadrenocorticism (cortisol deficiency) and even complete hypoadrenocorticism (cortisol and mineralocorticoid deficiency; Addison's disease) (1-8). Therefore, it is imperative to use the lowest daily dose possible and to monitor the dog very closely while on treatment with this drug.

The median dose used in the dogs of this retrospective study (4.75 mg/kg/day) was indeed within the dosage recommended on the Vetoryl package insert (2.2-6.7 mg/kg/ day) (9). However, that dose is much higher than the starting dose we normally recommend (≈2 mg/kg/day) (10). The higher doses given to the dogs of this report was the likely reason for the very high rate of hypocortisolism (53% of dogs), as well as the high rate of concurrent mineralocorticoid deficiency seen in these dogs (23% of dogs). Over the years, we have learned that lower starting doses are generally much safer and result in fewer severe side effects (11-15), and we have not personally had a dog develop complete hypoadrenocorticism for the last decade. Such high rates of hypoadrenocorticism generally indicate drug overdosage and are not acceptable, at least in our opinion.

We do not know from this abstract what initial dose was given, when the dogs were rechecked, or exactly how the investigators decided that a dosage increase was indicated. We recommend that dogs on trilostane treatment should be evaluated at 14 days, 1 month, 3 months, and every 3 months thereafter (10). At each recheck, we collect a complete history, do a complete examination, and perform a serum biochemical panel with electrolytes. In addition, we do an ACTH stimulation test at each visit by collecting the basal cortisol sample and administering cosyntropin (Cortrosyn) ≈3-4 hours after the morning trilostane dose to evaluate the peak effect on lowering cortisol levels.

We base dose adjustments on the dog's clinical response, routine blood tests, and cortisol testing. The ideal post-ACTH cortisol range that we recommend is 2.0-7.5 µg/dl (50-200 nmol/L). If`a dog continues to show clinical signs of hyperadrenocorticism and post-ACTH cortisol is above 7.5 µg/dl, we then increase the trilostane dose. If the signs of hyperadrenocorticism have resolved but the post-ACTH cortisol is above 7.5 µg/dl, we generally do not raise the daily dose but we would closely monitor for signs consistent with relapse.

If a Cushing's dog on trilostane is doing clinically well, but the serum cortisol values are low (post-ACTH cortisol less than 2 µg/dl [50 nmol/L]), we recommend that one stop the trilostane for 5-7 days and restart treatment at a 25-50% lower dose. Then, one should retest after 2 weeks of treatment on the new, lower dose. If the serum cortisol values remain subnormal on the reduced dosage, the trilostane should be discontinued indefinitely, with repeat ACTH stimulation testing scheduled for 1 month and every 3-6 months thereafter. The trilostane should only be restarted in these dogs if clinical signs of hyperadrenocorticism return and the post-ACTH cortisol concentrations once again become high. If Addison’s disease is confirmed (i.e., low cortisol concentrations with hyperkalemia, hyponatremia, or both), one should discontinue trilostane and treat the dog with glucocorticoids and mineralocorticoids, as needed.

Bottom line— The introduction of trilostane in many countries around the world has increased the options for the management of canine Cushing's disease. For most veterinarians, this drug has replaced the use of mitotane due to its greater safety. It is nearly as effective as mitotane and has a lower frequency of serious adverse reactions (15,16).

That all said, the drug can certainly lead to adverse side effects, including hypoadrenocorticism and adrenal necrosis (1-10). All of the side effects appear to be at least partially related to the dose given, so we recommend lower initial doses, close and frequent monitoring, and gradual increases in the daily dose as needed for control of clinical and biochemical signs of hyperadrenocorticism.

References:
  1. Neiger R, Ramsey I, O'Connor J, et al. Trilostane treatment of 78 dogs with pituitary-dependent hyperadrenocorticism. Vet Rec 2002;150:799-804. 
  2. Braddock JA, Church DB, Robertson ID, et al. Trilostane treatment in dogs with pituitary-dependent hyperadrenocorticism. Aust Vet J 2003;81:600-607.
  3. Wenger M, Sieber-Ruckstuhl NS, Muller C, et al. Effect of trilostane on serum concentrations of aldosterone, cortisol, and potassium in dogs with pituitary-dependent hyperadrenocorticism. Am J Vet Res 2004;65:1245-1250. h
  4. Chapman PS, Kelly DF, Archer J, et al. Adrenal necrosis in a dog receiving trilostane for the treatment of hyperadrenocorticism. J Small Anim Pract 2004;45:307-310. 
  5. Reusch CE, Sieber-Ruckstuhl N, Wenger M, et al. Histological evaluation of the adrenal glands of seven dogs with hyperadrenocorticism treated with trilostane. Vet Rec 2007;160:219-224.
  6. Ramsey IK, Richardson J, Lenard Z, et al. Persistent isolated hypocortisolism following brief treatment with trilostane. Aust Vet J 2008;86:491-495. 
  7. Richartz J, Neiger R. Hypoadrenocorticism without classic electrolyte abnormalities in seven dogs. Tierarztliche Praxis Ausgabe K, Kleintiere/Heimtiere 2011;39:163-169. 
  8. Griebsch C, Lehnert C, Williams GJ, et al. Effect of trilostane on hormone and serum electrolyte concentrations in dogs with pituitary-dependent hyperadrenocorticism. J Vet Intern Med 2014;28:160-165. 
  9. Dechra Animal Heath website. Veteryl Product Insert
  10. Melián CM, Pérez-Alenza D, Peterson ME. Hyperadrenocorticism in dogs In: Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine: Diseases of the Dog and Cat (Seventh Edition) Philadelphia, Saunders Elsevier, pp 1816-1840, 2010. Seventh ed. Philadelphia: Saunders Elsevier, 2010;1816-1840.
  11. Vaughan MA, Feldman EC, Hoar BR, et al. Evaluation of twice-daily, low-dose trilostane treatment administered orally in dogs with naturally occurring hyperadrenocorticism. J Am Vet Med Assoc 2008;232:1321-1328. 
  12. Arenas C, Melian C, Perez-Alenza MD. Evaluation of 2 trilostane protocols for the treatment of canine pituitary-dependent hyperadrenocorticism: twice daily versus once daily. J Vet Intern Med 2013;27:1478-1485. 
  13. Braun C, Boretti FS, Reusch CE, et al. Comparison of two treatment regimens with trilostane in dogs with pituitary-dependent hyperadrenocorticism. Schweiz Arch Tierheilkd 2013;155:551-558. 
  14. Feldman EC. Evaluation of twice-daily lower-dose trilostane treatment administered orally in dogs with naturally occurring hyperadrenocorticism. J Am Vet Med Assoc 2011;238:1441-1451. 
  15. Clemente M1, De Andrés PJ, Arenas C, et al. Comparison of non-selective adrenocorticolysis with mitotane or trilostane for the treatment of dogs with pituitary-dependent hyperadrenocorticism. Vet Rec 2007;15;161:805-809.
  16. Griffies JD. Old or new? A comparison of mitotane and trilostane for the management of hyperadrenocorticism. Compend Contin Educ Vet 2013;35:E3. 


Kool MMJ, Galac S, van der Helm N, Corradini S, Kooistram HS, Mol JA. Targeting Phosphatidylinositol-3-Kinase Signaling in Canine Cortisol-Secreting Adrenocortical Tumors - Novel Therapeutic Prospects? J Vet Intern Med 2014;28:1030.

     Hypercortisolism is one of the most common endocrinopathies in dogs, and is caused by cortisol- secreting adrenocortical adenomas or carcinomas in 15% of cases. The aim of this study was to investigate involvement of the insulin-like growth factor (IGF)-phosphatidylinositol-3-kinase (PI3K) signaling pathway in the pathogenesis of adrenocortical tumors (ATs), in order to identify components of this pathway that may hold promise as future therapeutic targets, prognostic and/or diagnostic markers.
     The tumor group consisted of histologically confirmed cortisol-secreting adenomas (n = 14) and carcinomas (n = 30). Whole tissue explants of normal adrenal glands (n = 10) were used as controls. Quantitative RT-PCR was used to assess the relative mRNA expression levels of IGF1 and 2, IGF- and EGF-receptors, IGF-binding proteins, PI3K inhibitor PTEN and downstream target genes of the PI3K signaling pathway. Localization of PTEN was immunohistochemically evaluated. Additionally, mutation analysis was performed on the full coding region of PTEN and the PI3K catalytic subunit, on mRNA level.
     When compared to normal adrenals, in carcinomas the differential expression of PI3K target genes indicated activation of the pathway. Also, carcinomas showed a decreased expression of PI3K inhibitor PTEN and an increased expression of the EGF receptor ErbB2. Gene expression levels in adenomas were mostly unchanged. Immunohistochemical staining of PTEN was predominantly negative in both ATs and normal adrenals. No missense mutations of PTEN and the PI3K catalytic subunit were detected.
     Based on gene function and reports in human ATs, the low expression of PTEN in carcinomas is of particular interest with regard to tumor pathogenesis. Target gene expression suggests PI3K activation in carcinomas, possibly due to decreased PTEN and/or increased ErbB2 expression. Based on these results, targeting of ErbB2, PI3K or its downstream effectors may have potential as a therapeutic option in canine cortisol-secreting adrenocortical carcinomas.

Comments—To adequately understand the importance of this investigational study the molecular biology of PI3Ks, PTEN, IGF-1 and IGF-2, IGF- and EGF- receptors and IGF- binding proteins and their link to adrenocortical tumors is briefly reviewed.

Phosphoinositide 3-kinases (also called PI3Ks) are a family of enzymes involved in cellular functions such as cell growth, proliferation, differentiation, and survival (1). More specifically, PI3Ks phosphorylate cell membrane lipids to modulate the activity of intracellular protein effectors that regulate many aspects of cell function. For example, it is estimated that every cell has 50-100 “downstream” effectors of PI3Ks. In essence, the PI3K pathway is an intracellular signaling pathway important in apoptosis and hence cancer and longevity. In many cancers, this pathway is overactive, thus reducing apoptosis and allowing proliferation. Consequently, many experimental cancer drugs are designed to inhibit the signaling sequence at some point using PI3K inhibitors. Impact point: Expression of target genes suggests activation of the PI3K pathway in adrenocortical tumors.

Phosphatase and tensin homolog (PTEN) is a protein that, in humans, is encoded by the PTEN gene (2). PTEN acts as a tumor suppressor gene but is mutated in a large number of cancers with high frequency (3). When the PTEN protein is functioning properly, it acts as part of a chemical pathway that signals cells to stop dividing and can cause cells to undergo apoptosis when necessary. These functions prevent uncontrolled cell growth that can lead to the formation of tumors. Impact point: The low expression of PTEN and negative immunohistochemical staining with adrenocortical tumors suggests that lack of this PI3K inhibitor may play a role in tumor pathogenesis.

Epidermal growth factor or EGF is a growth factor that stimulates cell growth, proliferation, and differentiation by binding to its receptor EGFR (4). The epidermal growth factor receptor is a member of the ErbB family of receptors, a subfamily of four closely related receptor tyrosine kinases (ErbB1-4); receptor tyrosine kinases are the high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones (5). Increased activity of the receptor for EGF has been observed in certain types of cancer, often correlated with mutations in the receptor and abnormal function (8). Impact point: Adrenocortical tumors showed an increased expression of the ECG receptor ErbB-2.

Insulin-like growth factors (IGFs) are proteins with an amino acid sequence similar to insulin. IGFs are part of a complex system that cells use to communicate with their physiologic environment. This complex system (often referred to as the IGF "axis") consists of two cell-surface receptors (IGF1R and IGF2R), two ligands - insulin-like growth factor 1 (IGF-I) and insulin-like growth factor 2 (IGF-2), and a family of six high-affinity IGF-binding proteins which modulate IGF action in many ways (6). The IGF axis has been shown to play a key role in cancer cell proliferation, differentiation, and the inhibition of programmed cell death (apoptosis) using intracellular signaling through the PI3K pathway (see below). Impact point: Unlike in humans and for reasons that are unclear (see Bottom Line summary), the IGFs and IGF receptors apparently do not play a role in the pathogenesis of adrenocortical tumors in the dog.

The Bottom Line— To date, the most common treatment approach in dogs with an cortisol-secreting adrenal tumor is surgery and/or medical therapy with mitotane or trilostane (7-12). In human medicine, several novel approaches are under study for treatment of advanced adrenal carcinoma, many of which represent molecularly targeted therapies. For example, the finding that over 80% of adrenal tumors express the epidermal growth factor receptor (EGFR) (13, 14) provides a rationale for the study of agents that target the EGFR. In addition, approximately 80% of adrenocortical tumors also over express insulin-like growth factor type 2 (IGF-2), which is known to signal predominantly through the IGF-1 receptor (IGFR1).

Preclinical studies targeting the IGF-1 receptor (15) and two phase I trials have shown promising results (16, 17), and ongoing phase II and III trials are close to completion. The recent work by Kool et al in dogs, would suggest that targeting a specific EGFR (i.e., ErbB2) or PK3K or its downstream effectors may have potential as a therapeutic option in canine cortisol-secreting adrenal tumors. Clearly more investigational studies are needed to determine the efficacy, adverse effects, and cost of molecular targeting therapy before it becomes an accepted form of treatment for adrenocortical tumors in the dog.

References:
  1. Vanhaesebroeck B, Stephens L, Hawkins P. PI3K signaling: the path to discovery and understanding. Nat Rev Mol Cell Biol 2012;13:195-203.
  2. Steck PA, Pershouse MA, Jasser SA, et al. Identification of a candidate for a tumor suppressor gene that is mutated in multiple advanced cancers. Nat Genet 1997;15: 356–62.
  3. Chu EC, Tarnawski AS. PTEN regulatory functions in tumor suppression and cell biology. Med Sci Monit 2004; 10:235–41.
  4. Herbst RS. Review of epidermal growth factor receptor biology. Int J Radiat Oncol Biol Phys 2004;59 (2 Suppl): 21–26.
  5. Zhang H, Berezov A, Wang Q, et al. ErbB receptors: from oncogenes to targeted cancer therapies. J Clin Invest 2007;117:2051–2058.
  6. Le Roith D. Insulin-like growth factors. N Engl J Med 1997; 336; 633-640.
  7. van Sluijs FJ1, Sjollema BE, Voorhout G, et al. Results of adrenalectomy in 36 dogs with hyperadrenocorticism caused by adrenocortical tumor. Vet Q 1995;17:113-116.
  8. Anderson CR, Birchard SJ, Powers BE, et al. Surgical treatment of adrenocortical tumors: 21 cases (1990-1996). J Am Anim Hosp Assoc 2001;37:93-97.
  9. Scavelli TD, Peterson ME, Matthiesen DT. Results of surgical treatment for hyperadrenocorticism caused by adrenocortical neoplasia in the dog: 25 cases (1980-1984). J Am Vet Med Assoc 1986;189:1360-1364.
  10. Kintzer PP, Peterson ME. Mitotane treatment of 32 dogs with cortisol-secreting adrenocortical neoplasms. J Am Vet Med Assoc 1994;205;54-60.
  11. Feldman EC, Nelson RW, Feldman MS, et al. Comparison of mitotane treatment for adrenal tumor versus pituitary-dependent hyperadrenocorticism in dogs. J Am Vet Med Assoc 1992;200:1642-1647
  12. Helm JR, McLauchlan G, Boden LA, et al. Comparison of factors that influence survival in dogs treated with mitotane and trilostane with adrenal-dependent hyperadrenocorticism. J Vet Intern Med 2011;25:251-260.
  13. Edgren M, Eriksson B, Wilander E, et al. Biological characteristics of adrenocortical carcinoma: a study of p53, IGF, EGF-r, Ki-67 and PCNA in 17 adrenocortical carcinomas. Anticancer Res 1997;17:1303-1309.
  14. Kamio T, Shigematsu K, Sou H, et al. Immunohistochemical expression of epidermal growth factor receptors in human adrenocortical carcinoma. Hum Pathol 1990; 21:277-282.
  15. Barlaskar FM, Spalding AC, Heaton JH, et al. Preclinical targeting of the type I insulin-like growth factor receptor in adrenocortical carcinoma. J Clin Endocrinol Metab 2009;94:204-212.
  16. Haluska P, Worden F, Olmos D, et al. Safety, tolerability, and pharmacokinetics of the anti-IGF-1R monoclonal antibody figitumumab in patients with refractory adrenocortical carcinoma. Cancer Chemother Pharmacol 2010;65:765–773.
  17. Carden CP, Frentzas S, Langham M, et al. Preliminary activity in adrenocortical tumor (ACC) in phase I dose escalation study of intermittent oral dosing of OSI-906, a small-molecule insulin-like growth factor-1 receptor (IGF-1R) tyrosine kinase inhibitor in patients with advanced solid tumors. J Clin Oncol 2009; 27:1344.


Thursday, July 3, 2014

Top Clinical Endocrinology Research Abstracts, 2014 ACVIM Forum: Diabetes Part 3


Following last week’s post, this is the next installment of my review of the "top 12 list" of clinical endocrinology research abstracts presented at this year's American College of Veterinary Internal Medicine Forum.

As with last week's post, I've enlisted the help of Dr. Rhett Nichols, a well-known expert in endocrinology and internal medicine whose day-job is senior member of the veterinarian consulting service for Antech Diagnostics, the world's largest laboratory dedicated to animal health.  Rhett also serves as a consultant for the Animal Endocrine Clinic, so I talk to him almost every day about the more difficult cases I see in my practice.

In this post, we will review another of these "top 12" abstracts (finishing up with the diabetes abstracts). Next week, we will turn to the top clinical abstracts dealing with the adrenal gland, and then finish with disorders of the thyroid over the next 2 weeks. We hope you agree with our selections, but if you don't, remember that you can always post a comment and add your opinion.


Bertalan AV, Drobatz KJ. Hess RS. NPH and Lispro Insulin for Treatment of Dogs with Diabetes Mellitus. J Vet Intern Med 2014;28:1026.

Some dogs, treated with twice-daily NPH insulin and Hill's W/D diet, have postprandial hyperglycemia despite having clinically well-regulated diabetes mellitus (DM). The goal of this study was to determine whether postprandial hyperglycemia and fructosamine concentration can be decreased by adding lispro insulin to the treatment protocol.
      Six dogs were enrolled into this ongoing prospective study. Dogs were enrolled if they had clinically well-regulated DM while treated with NPH insulin and W/D q12 hours and if they had postprandial hyperglycemia defined as an increase in blood glucose concentration (BG) within two hours of NPH insulin administration and feeding. Fructosamine was quantified and BG was measured just before feeding and NPH insulin administration (T0), every 30 minutes for the first 2
hours (T30, T60, T90, T120), and every two hours thereafter for eight additional hours. Dogs were then treated at home with the same NPH insulin dose and W/D, but a separate lispro insulin injection of 0.1 Unit/kg SC was added to the NPH insulin and W/D protocol. Serial BG and fructosamine were measured two weeks later and compared to the original values using the Wilcoxon Signed Rank Test. Median [range] fructosamine (400 μmol/L [289–624 μmol/L]), and BG at T60 (313 mg/dl [187–376 mg/dl]) and T90 (239 mg/dl [166–332 mg/dl]) were significantly higher before lispro insulin was introduced compared to two weeks later (390 μmol/L [253–486 μmol/L]), p = 0.046, 117 mg/dl [42–307 mg/dl]), p = 0.028, and 94 mg/dl [48–197 mg/dl]), p = 0.028, respectively). 
      It is concluded that addition of lispro insulin to an NPH and W/D treatment protocol may significantly decrease fructosamine and postprandial hyperglycemia.

Comments— In this study, addition of a rapid-acting insulin analog (insulin lispro; Humalog, Lilly) to a standard twice-daily NPH insulin regimen appeared to improve glycemic control in dogs with clinically controlled diabetes. This finding is not unexpected, since it is well known that the administration of a short-acting insulin at time of meals will help lessen post-prandial hyperglycemia and lead to improved overall glycemic control in diabetic patients (1-4).

Rapid-acting insulin analogs— Although human recombinant regular insulin is still used as a short-acting insulin by most veterinarians, this insulin has been replaced for the most part with one of the more rapid-acting insulin analogs in human medicine (5-7). One of these newer rapid-acting insulin analogs is insulin lispro, which was the first commercially available insulin analog produced (6,7). Compared with regular human insulin, this insulin analog offers the advantages of faster subcutaneous absorption, an earlier and greater insulin peak, and a shorter duration of action. Although not used frequently in dogs, insulin lispro has been reported by this same group of investigators to be as effective as regular insulin in the treatment of ketoacidosis (8).

Long-acting insulin analogs and analog mixtures—Like human regular insulin, use of human NPH insulin is gradually being phased out and replaced with a mixture of rapid- and long-acting insulin analogs (5-7, 9-11). For example, newly diagnosed insulin-dependent human patients may be treated with a combination of once to twice daily injections of glargine (Lantus) or detemir (Levemir), together with a rapid-acting analog (e.g., insulin lispro or aspart) given at time of meals (11-14). Pre-mixed combinations of a short-acting synthetic insulin analog (i.e., lispro or aspart insulin) with a longer-acting insulin analog (i.e., lispro or aspart protamine insulin) are also commercially available as Humalog Mix 75/25 (Eli Lilly) or NovoLog Mix 70/30 (Novo Nordisk) (5,10). Both of these insulin analog mixtures are given twice daily with meals.

Time interval between insulin injection and meal intake— When a short-acting insulin (either human recombinant regular insulin or lispro) is added to the overall insulin regimen, it is standard protocol that the rapid-acting insulin be given shortly prior to ingestion of the meal (2-4,15,16). This allows enough time for the injected insulin to be absorbed into the circulation and blunt the post-prandial rise in blood glucose concentration. If the insulin injection is delayed until after the meal, severe post-prandial hyperglycemia may develop, which can lead to a clinical state resembling insulin resistance in some patients.

Most veterinarians fail to consider the importance of the time interval between insulin injection and meal intake when evaluating glycemic control in their diabetic dogs on standard insulin protocols. Whenever possible, I like to have my owners inject insulin (NPH, Vetsulin, or NPH/regular combinations) about 20-30 minutes before the dog eats, which allows enough time for insulin to to be partially absorbed and prevent severe post-prandial hyperglycemia (17).  With a more rapidly absorbed insulin, such as lispro, the timing between insulin injection and feeding can likely be shortened to less than 20 minutes. Of course, administering insulin injections prior to feeding is not always possible or even advisable, especially if the dog's appetite is poor or variable.

It is unclear what the time interval was between insulin injection and meal intake in this study by Bertalan et al., since it was not stated. If not given prior to feeding, however, the results might have been improved by using such a protocol.

The Bottom Line— In dogs with problem diabetes, addition of a short-acting insulin to the overall insulin regime may be helpful, especially in those dogs that experience severe post-prandial hyperglycemia.  The interval between insulin injection and meal intake must be taken into consideration when employing this protocol, and the addition of a short-acting insulin would likely be less effective when injected after eating. In any case, further research needs to be done on the effect on the timing of insulin injections and meals in dogs with diabetes mellitus.

Although insulin lispro works well in dogs, a major disadvantage of using any insulin analog, including lispro, is the high cost. All of the insulin analogs are approximately 3 to 5 times more costly than conventional human recombinant NPH, regular, or mixtures of NPH 70/30 insulins.

On a practical basis, there is little reason to use insulin lispro over human regular insulin in dogs, especially when you consider the great difference in cost. Premixed NPH/regular insulin is commercially available as Humulin 70/30 (Eli Lilly) or Novolin 70/30. Both of these commercial preparations contain a 100 U/ml pre-mixed combination of 30% short-acting (regular insulin) and 70% intermediate-acting insulin (NPH). In the USA, the cheapest place to purchase human regular, NPH, and 70/30 combinations is at Walmart, which sells these insulins as the ReliOn Novolin brand for around $25 per vial (19).

Another option, of course, is porcine lente insulin (Caninsulin or Vetsulin), which is actually a mixture of rapid-acting and long-acting insulins (Semi-lente and Ultralente, respectively) (20,21). Although more expensive than the ReliOn Novolin 70/30 insulin, Vetsulin is certainly much more cost effective than any of the insulin analogues. With either insulin preparation, I like to give the injection about 20-30 minutes prior to feeding to ensure that adequate insulin concentrations will be present in the circulation when the meal is absorbed to blunt the rise in blood glucose concentration and help better control the diabetic state (17).

References:
  1. Brownlee M. Insulin treatment of diabetes. Hosp Pract 1979;14:85-94. 
  2. Phillips M, Simpson RW, Holman RR, et al. A simple and rational twice daily insulin regime. Distinction between basal and meal insulin requirements. Q J Med 1979;48:493-506. 
  3. Holman RR, Turner RC. A practical guide to basal and prandial insulin therapy. Diabet Med 1985;2:45-53. 
  4. Zinman B. Insulin regimens and strategies for IDDMDiabetes Care 1993;16 Suppl 3:24-28. 
  5. Hirsch IB. Insulin analogues. N Engl J Med 2005;352:174-183. 
  6. Campbell RK, Campbell LK, White JR. Insulin lispro: its role in the treatment of diabetes mellitus. Ann Pharmacother 1996;30:1263-1271. 
  7. Noble SL, Johnston E, Walton B. Insulin lispro: a fast-acting insulin analog. Am Fam Physician 1998;57:279-286, 289-292. 
  8. Sears KW, Drobatz KJ, Hess RS. Use of lispro insulin for treatment of diabetic ketoacidosis in dogs. J Vet Emerg Crit Care (San Antonio) 2012; 22:211-218.
  9. Kalra S. Newer basal insulin analogues: degludec, detemir, glargine. J Pak Med Assoc 2013;63:1442-1444. 
  10. Garber AJ. Premixed insulin analogues for the treatment of diabetes mellitus. Drugs 2006;66:31-49. 
  11. Hermansen K, Fontaine P, Kukolja KK, et al. Insulin analogues (insulin detemir and insulin aspart) versus traditional human insulins (NPH insulin and regular human insulin) in basal-bolus therapy for patients with type 1 diabetes. Diabetologia 2004;47:622-629. 
  12. Ashwell SG, Gebbie J, Home PD. Optimal timing of injection of once-daily insulin glargine in people with Type 1 diabetes using insulin lispro at meal-times. Diabet Med 2006;23:46-52. 
  13. Ashwell SG, Amiel SA, Bilous RW, et al. Improved glycaemic control with insulin glargine plus insulin lispro: a multicentre, randomized, cross-over trial in people with Type 1 diabetes. Diabet Med 2006;23:285-292. 
  14. Lucchesi MB, Komatsu WR, Gabbay MA, et al. A 12-wk follow-up study to evaluate the effects of mixing insulin lispro and insulin glargine in young individuals with type 1 diabetes. Pediatr Diabetes 2012;13:519-524. 
  15. MacGillivray MH, Mills BJ, Voorhess ML. Meal intolerance in type 1 diabetes mellitus: influence of time interval between insulin therapy and meal intake. J Med 1984;15:417-435. 
  16. Cobry E, McFann K, Messer L, et al. Timing of meal insulin boluses to achieve optimal postprandial glycemic control in patients with type 1 diabetes. Diabetes Technol Ther 2010;12:173-177. 
  17. Peterson ME. New development in the use of insulin mixtures and analogs for the problem diabetic. Proceedings of the 2013 American College of Veterinary Internal Medicine (ACVIM) Forum 2013;534-537.
  18. ReliOn Insulins. http://relion.com/diabetes/insulin
  19. Horn B, Mitten RW. Evaluation of an insulin zinc suspension for control of naturally occurring diabetes mellitus in dogs. Aust Vet J 2000;78:831-834. 
  20. Monroe WE, Laxton D, Fallin EA, et al. Efficacy and safety of a purified porcine insulin zinc suspension for managing diabetes mellitus in dogs. J Vet Intern Med 2005;19:675-682.

Thursday, June 26, 2014

Top Clinical Endocrinology Research Abstracts, 2014 ACVIM Forum: Diabetes Part 2



Following last week’s post, this is the next installment of my review of the "top 12 list" of clinical endocrinology research abstracts presented at this year's American College of Veterinary Internal Medicine Forum.

As with last week's post, I've enlisted the help of Dr. Rhett Nichols, a well-known expert in endocrinology and internal medicine whose day-job is senior member of the veterinarian consulting service for Antech Diagnostics, the world's largest laboratory dedicated to animal health.  Rhett also serves as a consultant for the Animal Endocrine Clinic, so I talk to him almost every day about the more difficult cases I see in my practice.

In this post, we will review 2 more of these "top 12" abstracts (both dealing with issues in diabetes), followed by the remaining 6 abstracts in the next 3 weeks' posts. We hope you agree with our selections, but if you don't, remember that you can always post a comment and add your opinion.


Claus P, Gimenes, AM, Castro, JR, Schwartz DS. Fructosamine Levels Do Not Agree with Clinical Classification Regarding Diabetic Compensation in Diabetic Dogs Under Treatment. J Vet Intern Med 2014;28:1034-1035.

Fructosamine levels are measured for diabetes management in veterinary medicine, but are rarely used in human clinical practice. A prospective, cross-sectional study was conducted between January 2010 and August 2012 to assess serum fructosamine levels of diabetic dogs under treatment in order to determine glycemic control compared to clinical classification of "compensated" versus "non-compensated," based on clinical signs and owner evaluation of the animal clinical status.
     The study population included 86 dogs: 25 were healthy, non-diabetic dogs (controls), 14 were diabetic dogs at diagnosis, 24 were diabetic under treatment (at least 30 days), and 23 had diabetic ketoacidosis (DKA).
     Compared to controls, serum fructosamine levels were significantly higher for all the diabetic groups, which were similar between each other. Considering all dogs, 8.3% were within the lower level (300–350 mg/dL), 11.9% had excellent glycemic control (350–400 mg/dL), 14.3% had good glycemic control (400–450 mg/dL), 14.3% had regular glycemic control (450–500 mg/dL) and 51.2% had poor control (> 500 mg/dL). Considering dogs under treatment, 95.8% were classified as having poor glycemic control and only 4.2% had a good control. Although 17/24 (70.8%) were clinically classified as "compensated," they all had fructosamine levels > 500 μmol/L; therefore, a poor glycemic control. Only one dog in this group had fructosamine levels indicating good glycemic control, but in this case, the owner had reported polyuria, polydipsia, polyphagia, and therefore, had been classified as non-compensated. Further studies must assess if insulin therapy adjustment based on fructosamine levels, and not only on clinical status, would lead to hypoglycemia episodes.

Study overview— Plasma fructosamine measurements are widely used as an indicator of glycemic control in diabetic dogs and cats (1-6). Because fructosamine is the product of an irreversible reaction between glucose and the amino groups of plasma proteins, it is assumed that its concentration reflects the mean blood glucose concentration of the preceding 1 to 2 weeks. Circulating fructosamine concentrations increase when glycemic control worsens and decrease when glycemic control improves.

In this abstract, the investigators determined that the vast majority (95.8%) of the 24 treated diabetic dogs would have been classified as having poor control, based on their high fructosamine levels (> 500 µmol/L). However, 17 of these 24 poorly-controlled dogs (based on the fructosamine level) were classified as well controlled or "compensated” diabetics based upon the history (i.e., no polyuria, polydipsia, or polyphagia). In contrast, 1 of the treated diabetic dogs was classified as having good control based on the fructosamine concentration, yet was classified clinically as an “uncompensated diabetic” because of owner complaints of continued polyuria, polydipsia and polyphagia. This discordancy between the clinical signs of diabetes and plasma fructosamine levels raised the question whether insulin dose adjustments could be based on fructosamine concentrations alone.

Comments—The discordancy between the clinical status of a treated diabetic patient (compensated versus uncompensated diabetes) and fructosamine levels that indicated poor control was somewhat surprising compared to the results of other published studies (1-4). However, there are several explanations that may account for these findings. These include the following:
  1. The fructosamine reference interval “cut-off values” are too low.
  2. Plasma Fructosamine is a “rear-view mirror” assessment of glycemic control.
  3. Circulating fructosamine concentrations can be quite variable.
Reference interval cut-offs: Reference ranges for plasma fructosamine concentrations differ slightly between laboratories (5). This difference is often due to the commercially-available fructosamine test kit, and the reagents used by each laboratory. Claus et al. adopted a fructosamine reference range where the cut-off for poor regulation is > 500 µmol/L, while others have adopted a wider reference range where the cut-off for poor regulation is defined as a fructosamine > 600 µmol/L (5,6). If the reference range cut-off in this study was raised, many of the dogs categorized as having poor regulation would likely be reclassified as having moderate control.

Rear-view mirror assessment: Many dogs require at least 8 weeks or more to establish adequate glycemic control (6). Fructosamine determinations at 30-60 days may be too early to accurately assess the status of diabetic regulation. In other words, the finding of high plasma fructosamine concentrations, when sampled at 30-60 days after the start on insulin therapy, may be misleading, since fructosamine concentrations reflect the mean blood glucose levels over the preceding 1 to 2 weeks.

Variability: The range of plasma fructosamine concentrations associated with a given blood glucose concentration can be quite wide, even after the fructosamine concentration has plateaued (4). For example in one study, fructosamine concentrations ranged from 400 to 633 µmol/L, with a blood glucose concentration of 523 mg/d (4). Given the large range of plasma fructosamine concentrations for a given glucose concentration, the range of fructosamine concentrations from well controlled and poorly-controlled diabetics will likely overlap.

The Bottom Line—Fructosamine is far from a perfect test, but despite its shortcomings, it remains a valuable adjunct parameter to monitor glycemic control. However, it should always be interpreted in conjunction with the history, physical exam findings and body weight and never used alone to adjust an insulin dose (1,5-7).

References:
  1. Reusch CE, Liehs MR, Hoyer M, et al. Fructosamine. A new parameter for diagnosis and metabolic control in diabetic dogs and cats. J Vet Intern Med 1993;7:177-182.
  2. Thoresen SI, Bredal WP. Clinical usefulness of fructosamine measurements in diagnosing and monitoring feline diabetes mellitus. J Small Anim Pract 1996:37;64-68.
  3. Crenshaw KL, Peterson ME, Heeb LA, et al. Serum fructosamine concentration as an index of glycemia in cats with diabetes mellitus and stress hyperglycemia. J Vet Intern Med1996:10:360-364.
  4. Link KR, Rand JS. Changes in blood glucose concentration are associated with relatively rapid changes in circulating fructosamine concentrations in cats. J Fel Med Surg 2008;10;583-592
  5. Reusch CE. Diabetic monitoring. In: Kirk’s Current Veterinary Therapy XV. Elsevier, St Louis, 2014; 193-199.
  6. Feldman EC, Nelson RW. Canine diabetes mellitus. In: Canine and Feline Endocrinology and Reproduction. 3rd ed, Elsevier, St Louis, 2004; 510.
  7. Briggs CE, Nelson RW, Feldman EC, et al. Reliability of history and physical examination findings for assessing control of glycemia in dogs with diabetes mellitus: 53 cases (1995-1998). J Am Vet Med Assoc 2000;217; 48-53.

Gostelow R, Scudder C, Keyte S, Forcada Y, Fowkes RC; Schmid HA, Church DB, Niessen SJM. Pasireotide (SOM230) Long-Acting Release Treatment for Feline Hypersomatotropism: A Proof of Concept Trial.  J Vet Intern Med 2014;28:1030.

Hypersomatotropism (HS) is a relatively common cause of feline diabetes mellitus. Attempts at its long-term medical management with somatostatin (sst) analogues have previously proven unrewarding. However, pasireotide (SOM230, Novartis, Basel, Switzerland), a novel sst analogue with binding affinity for sst receptor subtypes 1, 2, 3 and 5, was recently shown capable of decreasing serum insulin-like growth factor 1 (IGF-1) and improving insulin sensitivity in cats with HS when administered for 3 days as a short-acting, BID subcutaneous (SC) preparation. A long-acting release formulation (LAR) has been developed to allow convenient, once-monthly dosing and has led to successful biochemical control of human HS. The current study aimed to assess the potential of once-monthly pasireotide LAR as a treatment for feline HS.
      Feline HS was diagnosed in 12 diabetic cats based on increased serum IGF-1 (> 1000 ng/ml) and pituitary enlargement on computed tomography. Cats received 8 mg/kg SC pasireotide LAR once monthly for 6 months. Fructosamine concentration, IGF-1 concentration, and a 12-hour blood glucose curve (BGC) were performed at baseline and once monthly thereafter to monitor treatment response. A repeat CT-scan was performed at the end of the trial. A mixed-effects model was used to assess significance of changes in fructosamine, IGF-1 concentration, mean blood glucose (MBG) of BGCs, and insulin dose (U/kg).
       Seven of 12 cats completed the trial; 3 of 12 cats entered diabetic remission. Trial withdrawal occurred after a median of 2 months (range 1–4.5 months) due to persistence of uncontrolled diabetes mellitus (n = 1), diarrhoea (n = 2), a hypoglycemic event (n = 1), and an episode of diabetic ketoacidosis (n = 1). A significant decrease in IGF-1 (p < 0.001), insulin dose (p < 0.001), fructosamine (p = 0.04), though not MBG (p = 0.71) was documented. Adverse events included soft stools (9/12), worsening polyphagia (3/12), hypoglycaemia (4/12), and delayed hair regrowth (1/12). Maximum pituitary mass height had increased in 2/7, decreased in 4/7 and remained the same in 1/7 cats.
      In summary, pasireotide LAR is the first drug that shows potential to cause long-term biochemical and clinical improvement in cats with HS. In a proportion of cases, diabetic remission can even be achieved. Further work should focus on dose optimisation to enable higher success and lower withdrawal rates, specifically by trying to reduce adverse gastrointestinal events. The observed decrease in pituitary tumor size in some cats further establishes this as a useful primary, long-term treatment modality, although its preoperative use, enabling glycemic stabilization and tumor shrinkage before hypophysectomy, may also be of benefit.

Comments— Pasireotide (SOM230, trade name Signifor, Novartis) is an orphan drug approved for the treatment of Cushing’s disease in adult human patients when surgery has failed or is not an option (1). The drug is a somatostatin analog that targets multiple somatostatin receptors with high affinity. The result is apoptosis of those cells that produce ACTH, with significant lowering of plasma ACTH levels (2,3).

In addition, pasireotide has been shown to suppress GH and IGF -1 in rodents, as well as in human patients with acromegaly (4). Moreover, recent results of a phase III study of human patients treated with a long-acting release (LAR) form of pasireotide (Pasireotide LAR) showed that this novel form of therapy is significantly more effective than the current standard therapy with octreotide LAR or landreotide autogel (ATG) (5,6).

This study by Niessen's group showed that a once monthly injection of Pasireotide LAR to cats with acromegaly has the potential to cause a significant decrease in IGF-1 and GH levels, shrinkage of the GH-secreting pituitary tumor, and diabetic remission in cats with acromegaly.

The Bottom Line— To date, the only effectve treatment options for cats with acromegaly are transsphenoidal surgery or radiation therapy. Both of these treatments are quite costly and not widely available; in addition, they are associated with modest risk for patient morbidity and mortality and can have variable efficacy (7,8).

The idea that medical therapy for acromegaly is now a viable option is great news, but any new treatment that may change the therapeutic landscape for any disorder should be met with cautious optimism. In other words, it is important to remember that cats with acromegaly, just like in people with the same disorder, may have a variable response to medical therapy (9-12). For example, 5 of 12 cats in the current clinical trial had to be withdrawn from the study; 3 because of issues related to poor diabetes management and 2 because of diarrhea, which is a common adverse effect associated with somatostatin analogs. In addition, pituitary tumor shrinkage, which is a function of tumor size, tumor type (well differentiated versus poorly differentiated tumor cells), and the density and expression of specific somatostatin receptors, should not be expected to occur in all cases (9-12). Moreover, even if circulating GH values fall, diabetic remission or improved glycemic control may not occur for multiple reasons; for example, hyperglycemia is seen in a significant proportion of human patients treated with pasireotide, presumably because the drug inhibits insulin release (2-6).

And lastly, especially for cats, another drawback to use of pasireotide LAR is its high cost, which is estimated at $2000 per cat per year. However, it may be possible to use this agent at lower doses or at less frequent intervals, with obvious cost implications (13). Further research is obviously needed to determine these issues.

References:
  1. Signifor Official Site - Signifor (Pasireotide) Injection. Signifor. US. 
  2. Colao A, Petersenn S, Newell-Price J, et al. A 12-month phase 3 study of pasireotide in Cushing's disease. N Engl J Med 2012;366:914-924. 
  3. McKeage K. Pasireotide: a review of its use in Cushing's disease. Drugs 2013;73:563-574. http://www.ncbi.nlm.nih.gov/pubmed/23605695
  4. Petersenn S, Farrall AJ, Block C, et al. Long-term efficacy and safety of subcutaneous pasireotide in acromegaly: results from an open-ended, multicenter, Phase II extension study. 2014;17:132-140. 
  5. Colao A, Bronstein MD, Freda P, et al. Pasireotide versus octreotide in acromegaly: a head-to-head superiority study. J Clin Endocrinol Metab 2014;99:791-799. 
  6. Gadalha M, Bronstein M, Brue T, et al. Pasireotide LAR demonstrates superior efficacy versus Octreotide LAR and landreotide ATG in patients with inadequately controlled acromegaly: Results from a Phase III, multicenter, randomized study. 16th European Congress of Endocrinology. 2014; 35: P907. 
  7. Melmed S, Colao A, Barkan A, et al. Guidelines for acromegaly management: an update. J Clin Endocrinol Metab 2009;94:1509-1517. 
  8. Gittoes NJ, Sheppard MC, Johnson AP, et al. Outcome of surgery for acromegaly--the experience of a dedicated pituitary surgeon. QJM 1999;92:741-745. 
  9. Casarini AP, Jallad RS, Pinto EM, et al. Acromegaly: correlation between expression of somatostatin receptor subtypes and response to octreotide-lar treatment. Pituitary 2009;12:297-303. 
  10. Casarini AP, Pinto EM, Jallad RS, et al. Dissociation between tumor shrinkage and hormonal response during somatostatin analog treatment in an acromegalic patient: preferential expression of somatostatin receptor subtype 3. J Endocrinol Invest 2006;29:826-830. 
  11. Ezzat S, Kontogeorgos G, Redelmeier DA, et al. In vivo responsiveness of morphological variants of growth hormone-producing pituitary adenomas to octreotide. Eur J Endocrinol 1995;133:686-690. 
  12. Bhayana S, Booth GL, Asa SL, et al. The implication of somatotroph adenoma phenotype to somatostatin analog responsiveness in acromegaly. J Clin Endocrinol Metab 2005;90:6290-6295. 
  13. Turner HE, Thornton-Jones VA, Wass JA. Systematic dose-extension of octreotide LAR: the importance of individual tailoring of treatment in patients with acromegaly. Clin Endocrinol (Oxf) 2004;61:224-231. 

Thursday, June 19, 2014

Top Clinical Endocrinology Research Abstracts Presented at the 2014 ACVIM Meeting: Diabetes


Last week, I spent a week in Nashville, Tennessee attending the the 2014 American College of Veterinary Internal Medicine Forum. As part of that meeting, a number of research abstracts were presented (oral and poster presentations) that dealt with various aspects of canine and feline endocrinology. I plan to take the next four blog posts to discuss some of the newest and best research findings featured at the ACVIM meeting.

Of all of the excellent endocrine research abstracts presented, I've selected a "top 12 list" of the ones that have the most potential to change what I do in my clinical practice. To do this, I've enlisted the help of Dr. Rhett Nichols, a well-known expert in endocrinology and internal medicine whose day-job is senior member of the veterinarian consulting service for Antech Diagnostics, the world's largest laboratory dedicated to animal health. However, since Rhett also serves as a consultant for the Animal Endocrine Clinic (my practice), it was not that difficult to get him involved in this project!

In this post, we will review 3 of these top 12 abstracts, followed by the remaining 9 abtracts in the upcoming 3 posts. We hope you agree with our selections, but if you don't, remember that you can always post a comment and add your opinion.


Borin-Crivellenti S, Bonagura, JD, Gilor G. Comparison of Precision and Accuracy of U100 and U40 Insulin Syringes. J Vet Intern Med 2014;28:1029.

Day-to-day variability of insulin action is an important factor in attaining glycemic control in diabetics. In part, this variability is caused by imprecise dosing of insulin. 

We hypothesized that a U40 insulin syringe (U40) would be more precise than a U100 insulin syringe (U100). We dispensed 1, 2.5, and 4 international unit (IU) of insulin using 24 syringes for each dose from a BD Ultra-Fine 0.3-cc U100 (1⁄2 Unit Markings) and a VetOne 0.3-cc U40. Each dose was weighed on an analytical scale, and accuracy (mean [± SD] of actual dose–target dose*100/target dose) and precision (the coefficient of variation [SD/Mean] of the actual dose) were calculated. The proportions of CID (clinically important deviation: ≥ ± 20% off target) outcomes were compared between syringe types. 

U40 was more accurate for 1, 2.5 and 4IU (13.2 ± 8.7%; 6.0 ± 2.76%; 3.2 ± 1.6%, respectively) than U100 (28.2 ± 15.4%; 10.7 ± 8.0%; 4.6 ± 2.9%, respectively) (p < 0.05). Precision was lowest for 1IU but improved with increasing dose (U40: 1IU = 15.8%, 2.5IU = 6.4%, 4IU = 3.5%; U100: 1IU = 15.1%, 2.5IU = 8.1%, 4IU = 3.3%). U40 was more precise than U100 for dosing of 2.5IU (p < 0.05) despite the 1/2-unit markings on U100. CID outcomes were more frequent in U100 vs. U40 in 1IU (16/24 vs. 8/24 respectively, p = 0.02) and 2.5IU (3/24 vs. 0/24 respectively, p = 0.07) but did not occur in 4IU. 

For administration of small insulin doses, U40 are more accurate and precise than U100 and are less likely to result in clinically important over- or under-dosing. These results favor the use of U40 for administration of small doses of insulin.

Comments— Although the administration of low doses of U100 insulin (e.g., glargine, detemir, NPH) is common practice in veterinary medicine, this study reveals remarkably high dose error when doses of 4 units or less of U100 insulin are administered.  Since similar findings were reported in human pediatric patients given low doses of insulin (1-3) one to two decades ago, the results of this study should not be all that surprising. The use of U100 syringes can be dangerously inaccurate with administering very low insulin doses, and the use of syringes with 1/2 unit markings has not been shown to improve accuracy or precision (3).

Most human diabetologists recommend diluting the insulin when low doses of U100 insulin must be given (1-3). However, one must remember that there are many problems associated with dilution of these U100 insulins (4,5). First of all, glargine should never be diluted under any circumstances. Other U100 insulins, such as NPH or detemir, can be diluted, but this may alter the absorption kinetics of the insulin. For NPH (Humulin N), one can obtain the special diluent from the insulin manufacturer (Eli Lilly) or the pharmacy. For detemir (Levemir, Novo Nordisk), the insulin manufacturer has a special diluting medium, but the company generally will not provide the diluent to veterinarians. Detemir can be diluted with sterile water or saline, but this dilutes the insulin's antimicrobial additive and increases the risk of bacterial contamination. Therefore, because of the risk of bacterial contamination and changes with efficacy, diluting detemir is not generally recommended (5).

In both human patients and dogs, the use of insulin pen devices have consistently shown to be more accurate than dosing with insulin syringes (2,3,6). In one recent veterinary report (6), an insulin pen device was found to be more accurate than the insulin syringes when low doses (<8 units) of insulin were administered. In that study, insulin syringes tended to over-deliver by approximately 20-25% for very low doses (1 unit). However, for higher doses (16 units), the insulin pen and insulin syringe were comparable in accuracy.

The Bottom Line—Administration of low doses of insulin can be very inaccurate and imprecise, especially when using a U100 insulin and syringe. Use of U40 insulin improves accuracy but still is far from perfect. Either dilution of U-100 insulin (if possible) or use of an insulin pen device will help to improve accuracy when low-dose insulin administration is required.

References:
  1. Casella SJ, Mongilio MK, Plotnick LP, et al. Accuracy and precision of low-dose insulin administration. Pediatrics 1993;91:1155-1157. 
  2. Gnanalingham MG, Newland P, Smith CP. Accuracy and reproducibility of low dose insulin administration using pen-injectors and syringes. Arch Dis Child 1998;79:59-62. 
  3. Keith K, Nicholson D, Rogers D. Accuracy and precision of low-dose insulin administration using syringes, pen injectors, and a pump. Clin Pediatr (Phila) 2004;43:69-74. 
  4. Pet Diabetes: Diluting insulin. http://petdiabetes.wikia.com/wiki/Diluting_insulin
  5. Roomp K, Rand JS. Management of diabetic cats with long-acting insulin. Vet Clin North Am Small Anim Pract 2013;43:251-266. 
  6. Burgaud S, Riant S, Piau N. Comparative laboratory evaluation of dose delivery using a veterinary insulin pen (abstract 121). Proceedings of the WSAVA//FECAVA/BSAVA Congress; 12-15 April 2012;567.

Hall MJ, Adin CA, Borin-Crivellenti S, Rudinsky AJ, Gilor C. Pharmacology of the GLP-1 Analog Liraglutide in Healthy Cats. J Vet Intern Med 2014;28:1025-1026.

GLP-1 is an intestinal hormone that induces glucose-dependent stimulation of insulin secretion while suppressing glucagon secretion and increasing beta cell mass, satiety and gastric-emptying time. Liraglutide is a fatty-acid derivative of GLP-1 with a protracted pharmacokinetic profile that is used in people for treatment of type II diabetes mellitus and obesity. The aim of this study was to determine the pharmacodynamics of liraglutide in healthy cats.

A hyperglycemic clamp was performed on day-1 (Clamp-I) and 13 (Clamp-II) in seven healthy cats. Liraglutide was administered subcutaneously (0.6 mg/cat) once daily on days 7 through 13. During the clamp blood glucose concentrations were measured every 5 minutes and 20% dextrose infusion was adjusted to achieve hyperglycemia (225 mg/dl) at 30 min and to maintain that level of glycemia for 60 min. Plasma insulin and glucagon concentrations were measured at -15, 0, 30, 45, 60, 75, and 90 min.

Weight loss was recorded in all cats at day 13 (9%; P = 0.006). Appetite was subjectively decreased in all cats and one cat was withdrawn on day 10 because of 48 hrs of anorexia. Compared to Clamp-I, there was a trend during Clamp-II towards increased 60 min total glucose infused (median [range] 29% [1-178%], P = 0.087) and insulin concentrations (47% [-11-234%], P = 0.084). Glucagon concentrations (P = 0.67) and baseline glucose concentrations (P = 0.66) did not differ significantly between clamps.

Liraglutide may aid in weight loss in overweight cats but further evaluation is needed to determine its efficacy on improving glycemic control in diabetic cats.


Rudinsky AJ, Adin CA, Borin-Crivellenti S, Hall MJ, Gilor C. The Pharmacology of Exenatide Extended-Release in Healthy Cats. J Vet Intern Med 2014;28:1026.

GLP-1 is an intestinal hormone that induces glucose-dependent stimulation of insulin secretion while suppressing glucagon secretion and increasing beta cell mass, satiety and gastric- emptying time. Exenatide extended-release (ER) is a microencapsulated formulation of the GLP- 1-receptor agonist exenatide. It has a protracted pharmacokinetic profile that allows a once- weekly injection to replace insulin therapy safely and effectively in type-II diabetic people.

Here we studied the pharmacology of exenatide-ER in six healthy cats. A single, subcutaneous injection of exenatide-ER (0.13 mg/kg) was administered on day 0. A hyperglycemic clamp was performed on days -7 (Clamp-I) and 21 (Clamp-II). During the clamp, blood glucose concentrations (BG) were measured every 5 minutes and 20% dextrose infusion was adjusted to achieve hyperglycemia (225 mg/dl) at 30 min and to maintain that level of glycemia for the subsequent 60 min. Plasma insulin and glucagon concentrations were measured at -15, 0, 30, 45, 60, 75, and 90 min. Glucose tolerance was defined as the amount of glucose required to maintain hyperglycemia during the 60 minutes of the clamp.

Comparing Clamp-1 to Clamp-2 using paired t-tests, fasting BG decreased (mean [± SD] = -11 ± 8 mg/dl, p = 0.02), glucose tolerance improved (median [range] +33% [4–138%], p = 0.04) and median glucagon concentrations decreased (-4.7% [0–12.1%], p = 0.04). Insulin concentrations did not differ significantly. No side effects were observed throughout the study.

Exenatide-ER was safe and effective in improving glucose tolerance 3 weeks after a single injection. Further evaluation is needed to determine its efficacy and duration of action in diabetic cats.



Comments on the above 2 GLP-1 studies— Exenatide and liraglutide belong to a class of agents referred to as incretin mimetics. These agents are novel therapeutic options for type 2 diabetes in humans (1). Incretins are hormones released from the gastrointestinal tract during a meal, which potentiate insulin secretion from the beta cells of the pancreas (2). The major and most potent incretin is glucagon-like peptide 1 or GLP-1 (3). The biological actions of GLP-1 is highly glucose dependent, and therefore hypoglycemia does not occur. Additional benefits include stimulation of insulin biosynthesis, beta cell proliferation, resistance to apoptosis, enhanced beta cell survival, and inhibition of glucagon secretion (4,5,6). Extrapancreatic effects include delayed gastric emptying, decreased gastrointestinal motility, and central nervous system effects of satiety and weight loss (4,7).

Because native GLP-1 is rapidly degraded by a ubiquitous enzyme, GLP-1 agonists that are resistant to enzyme degradation were developed (8).  Two agonists are now available commercially:
  1. Exenatide was the first GLP-1 agonist used for the treatment of type 2 diabetes in humans and was approved by the FDA in 2005. It is a synthetic peptide discovered in the saliva of the gila monster with a 53% homology with human GLP-1 (9). 
  2. Liraglutide was the first genetically engineered GLP-1 agonist and has a 97% homology with native GLP-1 (1,10). It was approved by the FDA in 2010. Adverse effects of these GLP-1 agonists in people include vomiting, nausea, inappetence, and acute pancreatitis (1,9,10).
In these two studies by investigators from The Ohio State University, the pharmacokinetics of the extended-release formulation of exenatide (exenatide-ER) given once SC over a 3 week period and liraglutide given SC daily for 7 days was evaluated in healthy cats using a common research tool called a hyperglycemic clamp (11). With this procedure, glucose is infused into the patient and “clamped”, or held at a certain concentration (225 mg/dl) over time. How much glucose that needs to be infused to keep the blood sugar at that constant high level is a measure of how fast glucose is metabolized. In essence, the hyperglycemic clamp is a way to quantify the beta cell response to glucose. The results of the study showed that all liraglutide-treated cats lost weight and subjectively had a decreased appetite. In addition, there was a trend toward increased glucose utilization and insulin secretion. The exenatide-ER treated cats showed increased glucose tolerance, with no side effects being observed.

The Bottom Line— Preliminary results in normal cats would suggest that liraglutide may aid in weight loss in overweight cats and exenatide-ER may improve glucose tolerance in preclinical and overt diabetic cats without causing adverse side effects.

Clearly, further evaluation of both these agents is needed to determine their efficacy in diabetic cats. The hope is that these agents could one day be used as monotherapy to improve glucose tolerance without causing hypoglycemia and, in addition, increase beta-cell mass with minimal adverse effects such as nausea, vomiting, and inappetence. One potential drawback to their wide use in the treatment of preclinical and overt diabetic cats is their considerable cost.

References:
  1. Gallwitz B. GLP-1 analogues for type 2 diabetes mellitus: current and emerging agents. Drugs 2011;72:1675-88
  2. Moore B. Edie ES, Abram JH. On the treatment of diabetes mellitus by acid extract of duodenal mucous membrane. Biochem J 1906;1;28-38
  3. Kim W, Egan JM. The role of incretins in glucose homeostasis and diabetes treatment. Pharmacol Rev 2008;60:470-512
  4. Drucker DJ. The biology of incretin hormones. Cell Metab 2006;3:153-65
  5. Li Y, Hansotia T, Yusta B, et al. Glucagon-like peptide-1 receptor signaling modulates beta cell apoptosis. J Biol Chem 2003;278:471-478. 
  6. Farilla L, Bulotta A, Hirshberg B, et al. Glucagon-like peptide 1 inhibits cell apoptosis and improves glucose responsiveness of freshly isolated human islets. Endocrinology 2003;144:5149-5158. 
  7. Drucker DJ, Nauck MA. The incretin system: glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors in type 2 diabetes. Lancet 2006;368:1696-1705. 
  8. Mudaliar S, Henry RR. The incretin hormones: from scientific discovery to practical therapeutics. Diabetologia 2012;55:1865-1868. 
  9. Eng J, Kleinman WA, Singh L, et al. Isolation and characterization of exendin-4, an exendin-3 analogue, from Heloderma suspectum venom. Further evidence for an exendin receptor on dispersed acini from guinea pig pancreas. J Biol Chem 1992;267:7402-7405. 
  10. Phillips LK, Prins JB. Update on incretin hormones. Ann N Y Acad Sci 2011;1243:E55-74. 
  11. DeFronzo RA, Tobin JD, Andres R. Glucose clamp technique: a method for quantifying insulin secretion and resistance. Am J Physiol 1979;237:E214-223. 

Thursday, June 12, 2014

Top Endocrine Publications of 2013: Hypertension in Dogs and Cats


In my sixth compilation of the canine and feline endocrine publications of 2013, I’m moving on to endocrine hypertension. Listed below are 13 research papers written in 2013 that deal with a variety of hypertensive topics of clinical importance, many of which directly involve one or more hormones.

These range from a review of the hypertension associated with diabetic nephropathy (1) to an overview of guidelines for antihypertensive therapy in dogs and cats (2); from diagnostic testing of primary hyperaldosteronism in cats (3) to the use of plasma metanephrines for diagnosis of pheochromocytoma in dogs (5); and from a case study of a dog that develop severe hypertension secondary to an overdose of phenylpropanolamine (4) to a study of the relationship between the degree of hypertension and the development of ocular changes in cats with chronic kidney disease (6).

Other publications included are a comparison of indirect blood pressure measurements using a non-invasive method, high-definition oscillometry to direct measurements using a radio-telemetry device in awake cats (7) to a study of the effect of body position on indirect measurement of systolic arterial blood pressure in dogs (10);  from a report of a case series of dogs and cats with hypertensive encephalopathy (8) to a study of the effect of intra-abdominal hypertension on the adrenal gland secretion of cortisol, aldosterone, epinephrine, and norepinephrine in dogs (13); and finally, from a report of high dietary salt intake and blood pressure in cats (9) to an investigation of the renin-angiotensin-aldosterone system in the pathogenesis of hypertension associated with hyperthyroidism in cats (12).

References:
  1. Bloom CA, Rand JS. Diabetes and the kidney in human and veterinary medicine. Vet Clin North Am Small Anim Pract 2013;43:351-365. 
  2. Buoncompagni S, Bowles MH. Treatment of systemic hypertension associated with kidney disease. Compend Contin Educ Vet 2013;35:E1. 
  3. Djajadiningrat-Laanen SC, Galac S, Boeve SAEB, et al. Evaluation of the oral fludrocortisone suppression test for diagnosing primary hyperaldosteronism in cats. J Vet Intern Med 2013;27:1493-1499. 
  4. Ginn JA, Bentley E, Stepien RL. Systemic hypertension and hypertensive retinopathy following PPA overdose in a dog. J Am Anim Hosp Assoc 2013;49:46-53. 
  5. Green BA, Frank EL. Comparison of plasma free metanephrines between healthy dogs and 3 dogs with pheochromocytoma. Vet Clin Pathol 2013;42:499-503. 
  6. Karck J, von Spiessen L, Rohn K, et al. Interrelation between the degree of a chronic renal insufficiency and/or systemic hypertension and ocular changes in cats. Tierarztliche Praxis Ausgabe K, Kleintiere/Heimtiere 2013;41:37-45. 
  7. Martel E, Egner B, Brown SA, et al. Comparison of high-definition oscillometry -- a non-invasive technology for arterial blood pressure measurement -- with a direct invasive method using radio-telemetry in awake healthy cats. J Feline Med Surg 2013; 15:1104-1115. 
  8. O'Neill J, Kent M, Glass EN, et al. Clinicopathologic and MRI characteristics of presumptive hypertensive encephalopathy in two cats and two dogs. J Am Anim Hosp Assoc 2013;49:412-420. 
  9. Reynolds BS, Chetboul V, Nguyen P, et al. Effects of dietary salt intake on renal function: a 2-year study in healthy aged cats. J Vet Intern Med 2013;27:507-515. 
  10. Rondeau DA, Mackalonis ME, Hess RS. Effect of body position on indirect measurement of systolic arterial blood pressure in dogs. J Am Vet Med Assoc 2013;242:1523-1527. 
  11. Tian Z, Shen Y, Liao H, et al. Carotid proliferative plaque formation in a canine model of chronic hypertension. J Investig Med 2013;61:995-1003. 
  12. Williams TL, Elliott J, Syme HM. Renin-angiotensin-aldosterone system activity in hyperthyroid cats with and without concurrent hypertension. J Vet Intern Med 2013;27:522-529. 
  13. Yu J, Fu X, Chang M, et al. The effects of intra-abdominal hypertension on the secretory function of canine adrenal glands. PLoS One 2013;8:e81795. 

Wednesday, June 4, 2014

Dog on Long-Term Thyroid Hormone Supplementation: Hypothyroid, Hyperthyroid, or Cushing's Syndrome?


My patient is an 11-year old, spayed female Spaniel-Mix, named Molly. She weighs 31 pounds (14.1 kg) and is slightly overweight, with a body condition score of 7/9. About 5 years ago, she was initially diagnosed as having hypothyroidism based upon clinical signs of hair loss, together with low serum concentrations of total thyroxine (T4) and free T4. Molly responded well to thyroid hormone replacement with brand-name levothyroxine (L-T4) at the dose of 0.2 mg, twice daily.

Over the following 3 years, the dog did well (complete hair regrowth), but the daily L-T4 dose was increased (to 0.3 mg, twice daily) based on post-pill serum T4 testing, done about 5 hours after administration of the morning dose.

About 2 years ago, Molly was seen for new hair loss, increased appetite, and polyuria and polydipsia (PU/PD). Results of a CBC and serum chemistry panel were considered to be normal, and a post-pill serum T4 concentration was low-normal at 1.5 µg/dl (40 nmol/L). A complete urinalysis was unremarkable, other than a urine specific gravity of 1.013. Based on Molly's relapse of her hair loss and low-normal post-pill T4, the L-T4 dose was increased to 0.4 mg, BID.

Follow-up thyroid testing 6 months later revealed a post-pill serum T4 value in the high-normal range (3.9 µg/dL; 50 nmol/L) so the L-T4 was maintained at 0.4 mg BID. At that time, the PU/PD had lessened, and the increased appetite had normalized so no further workup was recommended.

On followup 1 year later (now 5 months ago), Molly again presented with increased appetite and more severe PU/PD. Her post-pill total T4 concentration was quite high at was 10.1 µg/dl (130 nmol/L), so the dosage of LT4 was decreased to 0.2 mg, BID. Repeat testing 2 months later revealed that the serum T4 value remained high (5.5 µg/dL; 70 nmol/L) so administration of L-T4 was discontinued. Other than truncal hair thinning, Molly's physical examination at that time was normal, with a normal heart rate (85 bpm); no thyroid masses could be palpated.

Now 3 months later, the owner reports progressive truncal hair loss, PU/PD, increased appetite, panting, and weight gain. Molly's physical exam was again unremarkable. Results of routine testing revealed a normal CBC (no stress leukogram), with severe hypercholesterolemia (660 mg/dL; 17.0 mmol/L). The serum alkaline phosphatase activity was also moderately high at 311 U/L (reference interval less than 100 U/L).

We next ran a complete thyroid profile, with the following results:
  • Total T4: 16 nmol/L (reference interval, 11-60 nmol)
  • Total T3: 0.4 nmol/L (reference interval, 0.8-2.1 nmol)
  • Free T4 by dialylsis: 12 pmol/L (reference interval, 10-50 pmol/L)
  • TSH: 1.0 ng/ml (reference interval, 0-0.6 ng/ml)
  • Thyroglobulin autoantibodies: 10% (reference interval, 0-35%)
I'm at a loss. I thought that the dog's signs might indicate hyperthyroidism but these results appear to be most consistent with hypothyroidism. Should L-T4 be restarted? We have only used a single brand-name L-T4 preparation in this dog — should we switch to another product?

Should I be testing Molly's pituitary-adrenal axis to rule out Cushing's syndrome?

My Response:

This dog is indeed a rather complicated case. Looking back at the history, Molly has displayed clinical signs of hair loss, PU/PD, and increased appetite for the past 2 years. All of these signs have waxed and waned in severity over this time, which explains her long duration of illness.

During that entire time, she was being treated with adequate replacement doses of thyroid hormone and never had post-pill T4 values that were low. In fact, many of her serum T4 concentrations checked during monitoring were too high— clearly in the hyperthyroid range (1). Overall, this strongly suggests that hypothyroidism alone cannot explain all the dog's problems, a conclusion that also is consistent with the fact that neither PU/PD nor increased appetite are signs of thyroid hormone deficiency (2,3).

Hypothyroid or hyperthyroid?
Given the fact that 2 of the post-pill serum T4 values were high, could this dog have iatrogenic hyperthyroidism secondary to an overdosage of L-T4? That certainly is possible, and thyrotoxicosis could account for the increased appetite and PU/PD (4-6). In fact, almost all hyperthyroid dogs will develop moderate to marked PU/PD, which is a much more prominent sign in dogs than in most cats with hyperthyroidism (7).

However, these signs persisted for 3 months after we stopped all thyroid hormone supplementation. In addition, the last thyroid hormone panel showed low to low-normal serum concentrations of total T4, T3, and free T4, in conjunction with high serum concentration of TSH; this combination of results is most consistent with primary hypothyroidism (the original diagnosis) (2,3). Overall, these findings completely rule out either natural hyperthyroidism associated with a hyperfunctional thyroid tumor or iatrogenic thyrotoxicosis from overdosage of L-T4 (5-7).

Hypothyroid or Cushing's syndrome?
Since Molly's clinical signs are also classical for hyperadrenocorticism, we should consider testing for that common canine disorder. While the high cholesterol concentration could be due to hypothyroidism or Cushing's syndrome, the finding of a high serum alkaline phosphatase activity certainly is consistent with chronic cortisol excess (8,9).

Before embarking on a workup for spontaneous Cushing's syndrome, remember to first make sure that Molly is not on any exogenous steroids, including a topical preparation for her eyes, ears, or skin, which can result in iatrogenic hyperadrenocorticism. You determine that not only by reviewing the record to see what your hospital has dispensed, but also by asking the owner what they're using to treat their dog, as they may have bags of steroid medications at home that weren't dispensed by you.

If Molly is suffering from Cushing's syndrome, it is possible that chronic cortisol excess is contributing to the low serum thyroid hormone concentrations.  Canine Cushing's syndrome can actually produce a secondary form of hypothyroidism, one that is reversible upon correction of the hyperadrenocorticism (10,11). However, it is very unlikely that Molly has had undiagnosed Cushing's disease for the past 5 years, given that she appears to be doing so well clinically. In addition, chronic cortisol excess suppresses serum TSH values (9,11), so Molly's high TSH value goes along more with primary hypothyroidism than a secondary form of hypothyroidism resulting from Cushing's syndrome.

As you continue to work up this dog, I would restart your thyroid hormone supplementation at a low dose (0.2-0.3 mg per day, divided). The dog certainly appears to be hypothyroid, based on the last serum thyroid profile, as well as worsened hair loss.

Causes of marked variation in L-T4 absorption
The marked variation in serum post-pill T4 concentrations are both interesting, as well as somewhat perplexing.

I'd start by questioning the owners about the timing of L-T4 administration, since the absorption of the medication is known to be increased when given on an empty stomach, as compared to when administered with meals (12,13). Could some of the marked variation in her past serum post-pill T4 levels have been due to administration of the drug with meals on some occasions and on an empty stomach on others? 

Other drugs and medications can also have an effect on L-T4 absorption (14). In this dog, we must carefully record all dietary changes as well as any administered drugs or supplements, all of which could potentially alter the absorption of the L-T4 preparation. 

References:
  1. Dixon RM, Reid SW, Mooney CT. Treatment and therapeutic monitoring of canine hypothyroidism. J Small Anim Pract 2002;43:334-340. 
  2. Mooney CT, Shiel RE. Canine hypothyroidism In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Fourth ed. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;63-85.
  3. Mooney CT. Canine hypothyroidism: a review of aetiology and diagnosis. N Z Vet J 2011;59:105-114. 
  4. Bosje T, den Hertog E, Dijksta M. Does the T4 measurement belong in the standard blood analysis in polyuria/polydipsia? Tijdschr Diergeneeskd 2013;138:230-231. 
  5. Peterson ME. Hyperthyroidism and thyroid tumors in dogs In: Melian C, Perez Alenza MD, Peterson ME, et al., eds. Manual de Endocrinología en Pequeños Animales (Manual of Small Animal Endocrinology). Barcelona, Spain: Multimedica, 2008;113-125.
  6. Mooney CT. Canine hyperthyroidism In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;86-91.
  7. Nichols, R., Peterson ME. Investigation of polyuria and polydipsia In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Fourth ed. Gloucester: British Small Animal Veterinary Association, 2012;215-220.
  8. Herrtage ME, Ramsey IK. Canine hyperadrenocorticism In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology. Quedgeley, Gloucester: British Small Animal Veterinary Association, 2012;167-189.
  9. Melián CM, Pérez-Alenza D, Peterson ME. Hyperadrenocorticism in dogs In: Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine: Diseases of the Dog and Cat (Seventh Edition) Philadelphia, Saunders Elsevier, pp 1816-1840, 2010. Seventh ed. Philadelphia: Saunders Elsevier, 2010;1816-1840.
  10. Peterson ME, Ferguson DC, Kintzer PP, et al. Effects of spontaneous hyperadrenocorticism on serum thyroid hormone concentrations in the dog. Am J Vet Res 1984;45:2034-2038. 
  11. Ferguson DC, Peterson ME. Serum free and total iodothyronine concentrations in dogs with hyperadrenocorticism. Am J Vet Res 1992;53:1636-1640. 
  12. Lamson MJ, Pamplin CL, Rolleri RL, et al. Quantitation of a substantial reduction in levothyroxine (T4) absorption by food. Thyroid 2004;14:876.
  13. Le Traon G, Burgaud S, Horspool LJ. Pharmacokinetics of total thyroxine in dogs after administration of an oral solution of levothyroxine sodium. J Vet Pharmacol Ther 2008;31:95-101.
  14. Liwanpo L, Hershman JM. Conditions and drugs interfering with thyroxine absorption. Best Pract Res Clin Endocrinol Metab 2009;23:781-792.