Endocrinology - Diabetes, Thyroid and Adrenal Disease
Please scroll down for more information on the following topics:
- PZI and Low-Dose Insulin
- Oral Anti-Diabetic Drugs
- Methimazole for Feline Hyperthyroid Disease
- Transdermal Methimazole Applied to Ear of Hyperthyroid Cats
- Adrenal Disease in Male Ferrets
- Mitotane for Canine Hyperadrenocorticism
PZI and Low-Dose Insulin
The commercial production of traditional beef and/or pork insulins has declined as most human diabetic patients (the majority of the consumers) are being switched to human insulin products because of the reduced risk of allergic reactions. Protamine zinc insulin occurs as a sterile suspension of insulin modified by the addition of protamine sulfate and zinc chloride, and has a long duration of action (up to 30 hours). Therefore, treatment of many dogs and cats has been accomplished with once daily dosing of PZI.
U-20 and U-40 insulin allow for more accurate measurement of smaller doses required by many pets and birds. Use of U-100 insulin can result in morbidity or mortality caused by dosing errors.
Please call our compounding pharmacy for more information about these insulin preparations for animals.
Oral Anti-Diabetic Drugs
Oral anti-diabetic drugs “may be appropriate for cats that are in good overall health with early or mild clinical signs of diabetes and those with owners who are unwilling or unable to administer insulin injections.”
The oral hypoglycemic medication, glipizide, provides a viable therapeutic alternative to conventional insulin therapy with a positive therapeutic response in approximately 50% of diabetic cats with non-insulin-dependent disease. Response to glipizide therapy or lack thereof usually is evident within the first 4 to 6 weeks of treatment. Adverse side effects occurred in less than 10% of patients. The existence of residual beta cell function is necessary for response to glipizide therapy. Discontinuation of diabetogenic medications that may be contributing to insulin resistance is important.
According to Deborah S. Greco, DVM, Ph.D., diplomate ACVIM, glipizide has been used successfully to treat diabetes mellitus in cats at a dosage of 2.5 to 5 mg two times daily, when combined with dietary fiber therapy. Dr. Greco recommends evaluating the patient weekly or every two weeks for a period of 2 to 3 months. If the fasting blood sugar decreases to less than 200 mg/dL, the glipizide should be continued at the same dosage and the cat reevaluated in 3 to 6 months. If the fasting blood glucose remains >200 mg/dL after 2 to 3 months of therapy and the cat is still symptomatic (polyuria, polydipsia, weight loss), glipizide should be discontinued and insulin therapy instituted. If the blood glucose remains >200 mg/dL and the cat becomes asymptomatic, glipizide should be continued indefinitely and the cat rechecked in 3-6 months.
Vet Clin North Am Small Anim Pract 1995 May;25(3):599-615
Compendium 23(7), July 2001, 633-640
Methimazole for Feline Hyperthyroid Disease
“Methimazole is the drug of choice for the medical management of feline hyperthyroid disease. It is safer and more potent than propylthiouracil in blocking thyroid hormone synthesis. Use of the drug generally will bring serum T4 into normal ranges within 2 to 3 weeks… Adverse effects have been observed in approximately 15% of cats and generally are transient. Anorexia, vomiting, and transient lethargy have been reported. Serum antinuclear antibodies develop in many cats with long-term use of the drug. A glucocorticoid-responsive pruritus involving the face, ears, and neck may occur. In less than 2% of cases, thrombocytopenia or agranulocytosis have been reported in cats treated with [methimazole]. Withdrawal of the drug and provision of care for thrombocytopenia or agranulocytosis generally results in resolution… Cats on chronic methimazole therapy should be rechecked every 3 to 6 months to assay serum T4 levels and to check for signs of drug toxicity.”
Handbook of Veterinary Drugs, 2nd edition, ©1998, pp. 239-240
According to the International Journal of Pharmaceutical Compounding (Vol. 5, No. 2, March/April 2001, p. 96), “it could be theorized that transdermal administration would produce a … higher blood level of methimazole than that resulting from oral administration of the drug. A higher blood level of [methimazole] might result in a slightly greater risk of adverse effects, so drug therapy might need to be initiated at a slightly lower dose than that of the traditional oral dose.” The author of the article (GiGi Davidson, R.Ph., DICVP, North Carolina State University, College of Veterinary Medicine) states that anecdotal evidence indicates that this is true of “most transdermally administered doses of methimazole. The most measurable parameter for efficacy is the response of the serum T4 level.”
Note: Methimazole is also used to decrease renal toxicity of cisplatin in dogs.
Transdermal Methimazole Applied to Ear of Hyperthyroid Cats
The following six cats have received methimazole in a pluronic lecithin organogel (PLO) which the owners apply to the inner side of the ear. Overall, we have found this to be very effective therapy with good compliance. Transdermal administration can be particularly helpful for owners who have arthritis and those who have great difficulty “pilling” the cat. Methimazole doses have ranged from 2.5mg to 12.5 mg daily, divided into two doses.
- Cat #1 (S.A.): 17 years old, has been on methimazole 1.25mg/0.1 ml PLO to inside of ear twice daily for nine months. The owner reports that the medicine is easy to administer and absorbs well. I am pleased with the clinical results.
- Cat #2 (A.L.): 18 years old, has been using methimazole for six months. This cat was started on 3.5mg/0.1ml PLO BID. Several dosage adjustments were necessary. We increased the concentration of the transdermal gel to 5.0mg/0.1ml PLO, and the owner now applies 7.5mg/0.15ml PLO in the AM and 5mg/0.1ml in the PM. She places plastic wrap over her finger before applying the medication, which she has found to be much easier to use than pills, with no stress to the pet. She states the measurements on the topical dispenser are easy to read, and she needs to wash the cat’s ear to remove the coating left by the medication.
- Cat #3 (B.M.): was started on methimazole eight months ago at 5mg/0.1ml PLO BID. The dose was decreased to 2.5mg BID. The cat’s owner stated the medication was very easy to use. B.M. improved clinically and gained weight, and is no longer on the med.
- Cat #4 (S.O.): used medication once only.
- Cat #5 (D.O.): same owner as cat #4, received methimazole 2.5mg/0.05ml PLO BID for two months. No longer on medication.
- Cat #6 (M.B.): 19 years old, has received methimazole 1.25mg/0.1ml PLO BID for four months. The owner says the medication is easy to apply, and alternates ears. It is necessary to wipe the ear each day as the medication does leave a residue.
Francis Arsenault, D.V.M.
Adrenal Disease in Male Ferrets
Adrenal gland disease is a common problem in middle-aged to older ferrets. The disease results in one or both of the adrenal glands producing abnormal amounts of androgens and/or estrogens, and can cause hair loss, itching, vulvar enlargement in females, prostate enlargement in male ferrets which can block the flow of urine, and in rare cases, bone marrow suppression. Although not usually a serious health concern, ferrets may have no relief from the itching that is associated with this disease if it is not treated.
Flutamide is an androgen blocker that may help relieve prostatic enlargement. It is dosed at 10 mg/kg, PO, every 12-24 hours. Liver enzymes should be checked at one month and every six months thereafter. Mitotane may be effective in younger ferrets but may cause nausea and lethargy. Ketoconazole is usually ineffective.
Evelyn Ivey, DVM, Dip ABVP, San Diego Co VMA Conf Procd, Sep 2000
Mitotane for Canine Hyperadrenocorticism
In veterinary medicine, mitotane is used primarily for the medical treatment of pituitary-dependent hyper-adrenocorticism (PDH) and palliative therapy of adrenal carcinoma, usually in dogs. Systemic drug availability has been found to be very poor from intact tablets in fasted dogs, and best when the powdered drug is mixed in oil and poured on dog food. The interaction between food and mitotane probably contributes to the variation in clinical response of dogs treated with the drug, because it appears that the efficacy is improved considerably when the drug is given with food. Because of the potentially severe toxicity associated with mitotane, clients should be instructed to wear gloves during and wash their hands after administering the medication, and to keep the medication out of reach of children or pets. Dogs with concurrent diabetes mellitus may have rapidly changing insulin requirements during the initial treatment period, and should be closely monitored until they are clinically stable. Clients should be advised of the symptoms of acute hypoadrenocorticism.
Because of the potential severe toxicity associated with mitotane, clients should be instructed to wash their hands after administration and to keep the medication out of reach of children or pets.
Res Vet Sci 1987 Sep;43(2):160-5
Veterinary Drug Handbook, 2nd Edition, by Donald C. Plumb