The U.S. Food and Drug Administration has approved Felanorm, the first generic methimazole oral solution for treating hyperthyroidism in cats, providing veterinarians with a new therapeutic option for managing this common feline endocrine disorder. The approval, granted to Norbrook Laboratories, marks a significant milestone in veterinary medicine by offering an alternative to the brand name product Felimazole.
Generic Alternative to Established Treatment
Felanorm contains the same active ingredient as Felimazole (Dechra Limited), which received initial FDA approval on May 27, 2009. The FDA determined that Felanorm contains no inactive ingredients that may significantly affect the bioavailability of the active ingredient, ensuring therapeutic equivalence to the brand name product.
The generic formulation is supplied in 30 mL or 100 mL bottles with 1 mL and 5 mL dosing syringes, providing flexibility for different patient needs and treatment durations.
Addressing a Common Feline Health Challenge
Hyperthyroidism represents the most common endocrine disease in cats of middle-age and older. The condition occurs when the thyroid gland produces excessive hormones, leading to a constellation of clinical signs that significantly impact feline quality of life. Affected cats typically present with weight loss despite increased appetite, vomiting, hyperactivity, increased urination and drinking, diarrhea, breathing problems, and changes in their coat condition.
While hyperthyroidism has been documented in cats as young as 6 years, veterinary experts note an increased risk in senior and geriatric felines. Kelly A. St. Denis, MSc, DVM, DABVP, emphasized the importance of regular monitoring, stating that senior and geriatric cats should receive examinations every 6 months for disease surveillance.
Prescription Requirements and Safety Considerations
The FDA has designated Felanorm as a prescription-only medication, requiring professional veterinary expertise for proper diagnosis of feline hyperthyroidism and treatment determination. Continued veterinary monitoring remains essential to ensure appropriate dosing as the disease can progress over time.
The medication follows a specific dosing protocol, administered in 2.5 mg increments every 12 hours. Dose adjustments should be made in 2.5 mg increments, with a maximum total daily dosage of 20 mg divided into doses not exceeding 10 mg as a single administration.
Adverse Effects and Handling Precautions
According to Dechra, adverse effects most commonly 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 due to methimazole's anti-vitamin K activity.
Safety protocols for human handlers require the use of protective single-use, impermeable gloves (such as latex or nitrile) when administering the solution. Hands must be washed with soap and water following administration to prevent human exposure to the medication.
The approval of Felanorm provides veterinarians with additional therapeutic flexibility in managing feline hyperthyroidism while maintaining the established safety and efficacy profile of methimazole treatment.
