Active Ingredient(s):
Methimazole is a thioureylene antithyroid drug, which inhibits the synthesis of thyroid hormones. Methimazole (1-methylimidazole-2-thiol) is a white crystalline substance that is freely soluble in water. The chemical formula is C4H6N2S. Molecular weight is 114.16.

Dosage Form and Description:
Felanorm^® (methimazole) Oral Solution is available at 5 mg/mL in bottles containing 30 or 100 mL with a 1 mL dosing syringe that is calibrated in mg increments.

Indications:
Felanorm (methimazole) Oral Solution is indicated for the treatment of hyperthyroidism in cats.

Dosage and Administration:
Always include the Instructions for Preparing a Dose of Felanorm (methimazole) Oral Solution and the Information for Cat Owners with the prescription.

The starting dose of Felanorm Oral Solution 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 (e.g., an increase of 1.25 mg per dose). 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.

The product should be administered orally using the enclosed graduated dosing syringe. The syringe has measurements representing the mg dose of the product. Rinse the oral dosing syringe between uses. (See the Instructions for Preparing a Dose of Felanorm (methimazole) Oral Solution).
 

Storage:
Store at controlled room temperature 25°C (77°F) with excursions between 15°-30°C (59°-86°F) permitted. Keep the container tightly closed.

Human Warnings:
As with all methimazole products, wear protective, single-use, impermeable gloves (e.g., latex or nitrile) when administering the solution. Wash hands with soap and water after administration to avoid exposure to drug.

IMPORTANT SAFETY INFORMATION:
Felanorm^® (methimazole) Oral Solution: As with all methimazole products, wear protective single use, impermeable (e.g., latex or nitrile) gloves when administering the solution. The most commonly reported side effects in cats are anorexia, vomiting, head/facial pruritus or edema, depression/lethargy, weight loss, anemia, elevated liver enzymes, skin lesions, elevated BUN, diarrhea, and thrombocytopenia. In some reported cases, the patients recovered after adverse reactions were recognized, the drug was withdrawn, and veterinary care was applied. Methimazole has anti-vitamin K activity and may induce bleeding diathesis without evidence of thrombocytopenia. Not for use in pregnant or lactating queens. Not for use in cats with primary renal or hepatic failure, autoimmune disease, or with hematological disorders (see the full prescribing information for additional details). For full prescribing information, contact VIRBAC at 1-800-338-3659 or visit (link to PI). For full prescribing information, contact VIRBAC at 1-800-338-3659 or click here.

REFERENCES: 

¹ Kynetec Sales Data, U.K. (based on standard 2.5 mg dose).

² International Society of Feline Medicine Easy-To-Give award 2017 (NOTE: Thyronorm^® is the U.K. brand name for Felanorm; both share the exact same formulation).

³ Data on File.