Generic treatment receives FDA approval for cats with hyperthyroidism

Photo: Kristina Blokhin/Adobe Stock

A senior cat rests on a deck.

Officials it the FDA have approved the first generic methimazole oral solution for the treatment of hyperthyroidism in cats (Felanorm; Norbrook Laboratories).¹ Felanorm contains the same active ingredient as the brand name drug product (

; Dechra Limited²) that was first approved on May 27, 2009. Additionally, the FDA determined that Felanorm contains no inactive ingredients that may significantly affect the bioavailability of the active ingredient.¹

Hyperthyroidism is the most common endocrine disease in cats of middle-age and older. The disease occurs when the thyroid gland produces too many hormones, and may lead to weight loss despite eating more, vomiting, hyperactivity, increased urination and drinking, diarrhea, breathing problems, and changes in their coat. These signs and symptoms can affect a cat's quality of life in addition to creating more stress for the cat and the owner.³

Although hyperthyroidism has been reported in cats as young as 6 years, Kelly A. St. Denis, MSc, DVM, DABVP, noted there is an increased risk of the disease in older felines of senior or geriatric age. “It really falls in line that we should be giving our senior and geriatric cats in every 6 months for monitoring,” St. Denis said in a 2022 interview with dvm360.⁴

Felanorm is only available by prescription from a licensed veterinarian because professional veterinary expertise is needed to diagnose feline hyperthyroidism and to determine whether the drug is an appropriate treatment, according to the FDA. Continued veterinary monitoring is also needed to ensure that the dose continues to be appropriate to control the patient’s hyperthyroidism, as this disease can progress over time.¹

According to Dechra, adverse effects most often reported with methimazole include anorexia, vomiting, head or facial pruritus or edema, depression or lethargy, weight loss, anemia, elevated liver enzymes, skin lesions, elevated blood urine nitrogen, diarrhea and thrombocytopenia. The drug may also induce bleeding diathesis without evidence of thrombocytopenia because methimazole has anti-vitamin K activity.²

Humans administering methimazole oral solution should wear protective single use, impermeable (eg, latex or nitrile) gloves when administering the solution. Hands should also be washed with soap and water after administration of Felanorm to avoid exposure to the drug.¹

Felanorm is supplied in 30 mL or 100 mL bottles with 1 mL and 5 mL dosing syringes. The drug is dosed in 2.5 mg increments, every 12 hours, and 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.¹

References

1. FDA approves first generic methimazole for treating hyperthyroidism in cats. News release. FDA. July 9, 2024. Accessed July 9, 2024. https://www.fda.gov/animal-veterinary/cvm-updates/fda-approves-first-generic-methimazole-treating-hyperthyroidism-cats?utm_medium=email&utm_source=govdelivery
2. Our products: Felimazole Coated Tablets. Dechra. Accessed July 9, 2024. https://www.dechra-us.com/our-products/us/companion-animal/cat/prescription/felimazole-coated-tablets-methimazole-tablets#2-5mg
3. Yankowicz S. Health-related quality of life assessment tool for cats with hyperthyroidism. dvm360. May 9, 2024. Accessed July 9, 2024. https://www.dvm360.com/view/health-related-quality-of-life-assessment-tool-for-cats-with-hyperthyroidism
4. Marrapodi A. The challenges of diagnosing feline hyperthyroidism. dvm360. December 12, 2022. Accessed July 9, 2024. https://www.dvm360.com/view/the-challenges-of-diagnosing-feline-hyperthyroidism