Felimazole Coated Tablets (methimazole tablets)

How to Order Prescriptions

---

Description

Felimazole Coated Tablets (methimazole tablets) are indicated for the treatment of hyperthyroidism in cats.

Dosage and Administration

The starting dose of Felimazole Coated Tablets is 2.5 mg administered every 12 hours. Following 3 weeks of treatment, the dose should be titrated to effect based on individual serum total T4 (TT4) levels and clinical response. Dose adjustments should be made in 2.5 mg increments. The maximum total dosage is 20 mg per day divided, not to exceed 10 mg as a single administration. Hematology, biochemistry, and TT4 should be evaluated prior to initiating treatment and monitored after 3 weeks and 6 weeks of treatment. Thereafter, bloodwork should be monitored every 3 months and the dose adjusted as necessary. Cats receiving doses greater than 10 mg per day should be monitored more frequently.

Contraindications

Do not use in cats with hypersensitivity to methimazole, carbimazole or the excipient, polyethylene glycol.
Do not use in cats with primary liver disease or renal failure.
Do not use in cats with autoimmune disease.
Do not use in cats with hematological disorders (such as anemia, neutropenia, lymphopenia, or thrombocytopenia) or coagulopathies.
Do not use in pregnant or lactating queens. Laboratory studies in rats and mice have shown evidence of teratogenic and embryotoxic effects of methimazole.

Warnings

Methimazole has anti-vitamin K activity and may induce bleeding diathesis without evidence of thrombocytopenia.

Human Warnings

Not for use in humans. Keep out of reach of children. For use in cats only. Wash hands with soap and water after administration to avoid exposure to drug. Do not break or crush tablets. Wear protective gloves to prevent direct contact with litter, feces, urine, or vomit of treated cats, and broken or moistened tablets. Wash hands after contact with the litter of treated cats.

Methimazole is a human teratogen and crosses the placenta concentrating in the fetal thyroid gland. There is also a high rate of transfer into breast milk. Pregnant women or women who may become pregnant, and nursing mothers should wear gloves when handling tablets, litter or bodily fluids of treated cats.

Methimazole may cause vomiting, gastric distress, headache, fever, arthralgia, pruritus, and pancytopenia. In the event of accidental ingestion/overdose, seek medical advice immediately and show the product label to the physician.

Precautions

Use of Felimazole Coated Tablets in cats with renal dysfunction should be carefully evaluated. Reversal of hyperthyroidism may be associated with decreased glomerular filtration rate and a decline in renal function, unmasking the presence of underlying renal disease. Due to potentially serious adverse reactions such as hepatopathy, immune-mediated anemia, thrombocytopenia, and agranulocytosis, cats on methimazole therapy should be monitored closely for any sign of illness including anorexia, vomiting, head/facial pruritus or edema, depression/lethargy, weight loss, anemia, skin lesions, diarrhea, fever, or lymphadenopathy. If a cat becomes ill while on Felimazole Coated Tablets, the drug should be stopped and appropriate hematological and biochemical testing should be done.

Anticoagulants may be potentiated by the anti-vitamin K activity of Felimazole Coated Tablets. Concurrent use of phenobarbital may reduce the clinical effectiveness of Felimazole Coated Tablets. A reduction in dose of certain drugs (β-adrenergic blocking agents, digitalis glycosides, and theophylline) may be needed when the patient becomes euthyroid.

Methimazole is known to reduce the hepatic oxidation of benzimidazole anthelmintics (e.g. fenbendazole), leading to increased plasma concentration of these anthelmintics when administered concurrently.

Felimazole Coated Tablets caused delayed maturation of the testes in young male cats in the 12-week safety study. See ANIMAL SAFETY. The safety of Felimazole Coated Tablets has not been evaluated in male cats intended for breeding.

Storage Information

Store at a controlled room temperature 25ºC (77ºF) with excursions between 15º-30ºC (59º-86ºF) permitted. Keep the container tightly closed in order to protect from moisture.