FDA approves first generic methimazole tablet for feline hyperthyroidism

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The FDA has approved the first generic form of methimazole tablets for treating hyperthyroidism in cats. According to the FDA, the product—Methimazole Coated Tablets, developed by Felix Pharmaceuticals—received full FDA evaluation to ensure the tablets are the bioequivalent to the brand-name product Felimazole Coated Tablets by Dechra, which received FDA approval in May 2009 following a review of the product’s safety, effectiveness, and adequacy of the manufacturing process.¹

Methimazole Coated Tablets come in 2.5 mg and 5 mg doses and are orally administered. The medication is dosed at 2.5 mg to start. Any adjustments to the dose should be made in 2.5 mg increments. The maximum daily dose should not exceed 20 mg, divided into doses of no more than 10 mg for each single administration.^1,2

Only a licensed veterinarian can prescribe Methimazole Coated Tablets. “[P]rofessional veterinary expertise is needed to diagnose hyperthyroidism in cats and to determine whether Methimazole Coated Tablets are an appropriate treatment,” the FDA wrote in a news release.¹ “Continued veterinary monitoring is also needed to ensure that the dose continues to be appropriate to control the cat’s hyperthyroidism, as this disease can progress over time.”

After administering Methimazole Coated Tablets, veterinarians should wash their hands with soap and water to prevent exposure to the drug.

The FDA approval of Methimazole Coated Tablets follows an earlier approval of generic methimazole in a liquid oral solution for the treatment of hyperthyroidism in cats (Felanorm; Norbrook Laboratories), which was cleared by the FDA earlier this month. Both Felanorm and Felimazole contain the same active ingredient.³

Felanorm comes in 30 mL or 100 mL bottles with 1 mL and 5 mL dosing syringes and should also be administered in 2.5 mg increments every 12 hours.³ Like Methimazole Coated Tablets, the maximum total dosage of Felanorm is 20 mg per day divided, not to exceed 10 mg as a single administration.³

A prevalent disease in cats, hyperthyroidism mainly affects cats who are middle-aged and older.³ Common clinical signs of hyperthyroidism include weight loss, increased appetite, polydipsia, and polyuria. Other signs include vomiting; diarrhea; hyperactivity; and an unkempt, matted, or greasy coat.⁴

Diagnosis consists of a physical examination, which includes palpating the patient’s neck area to feel for an enlarged thyroid gland. Heart rate and blood pressure can also be taken. If thyroid disease is suspected, a blood chemistry panel should be ordered, as well as an analysis of thyroid hormone levels.⁴

According to Cornell University, although the majority of feline patients with hyperthyroidism have elevated levels of the thyroid hormone T4 in their bloodstream, a small percentage of affected cats have T4 levels within the normal range.⁴ If hyperthyroidism is suspected but T4 levels are within the normal range, additional tests should be considered.

Treatment options include medication, radioactive iodine therapy, surgery, and dietary therapy. Overall patient health status, owner compliance with medicating the patient, and financial circumstances will influence the chosen treatment approach.⁴

References

1. FDA approves first generic Methimazole Coated Tablets for treating hyperthyroidism in cats. News release. US Food and Drug Administration. July 22, 2025. Accessed July 22, 2025. https://www.fda.gov/animal-veterinary/cvm-updates/fda-approves-first-generic-methimazole-coated-tablets-treating-hyperthyroidism-cats?utm_medium=email&utm_source=govdelivery
2. Freedom of Information Summary: ANADA 200-814. FDA. June 27, 2025. Accessed July 22, 2025. https://animaldrugsatfda.fda.gov/adafda/app/search/public/document/downloadFoi/17172
3. Coppock K. Generic treatment receives FDA approval for cats with hyperthyroidism. dvm360. July 9, 2025. Accessed July 22, 2025. https://www.dvm360.com/view/generic-treatment-receives-fda-approval-for-cats-with-hyperthyroidism
4. Hyperthyroidism in cats. Cornell Feline Health Center. Accessed July 22, 2025. https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/hyperthyroidism-cats#:~:text=Suggested%20Articles,and%20increased%20thirst%20and%20urination.