Treatment of Feline Hyperthyroidism with Carbimazole

Frenais, R., et al., Clinical efficacy and safety of a once-daily formulation of carbimazole in cats with hyperthyroidism. J Small Anim Pract, 2009. 50(10): p. 510-5.

Traditionally, medical treatment of feline hyperthyroidism has involved daily use of the azole drugs, methimazole or its pro-drug, carbimazole. Many cats require twice daily treatment with these drugs. A novel controlled-release formulation of carbimazole (Vidalta) has been developed by Intervet. These researchers evaluated the efficacy and safety of this new carbimazole formulation via a multi-center study of 44 client-owned cats with hyperthyroidism. Treatment was started at 15 mg/cat once daily, and dose was adjusted as required. Cats were followed for 53 weeks. The median dose over the study period was 10-15 mg/cat once daily. Clinical signs improved in almost all cats within 3 weeks after treatment was started. An increase in blood urea nitrogen (BUN) was noted in 25% of the cats, eosinophilia was noted in 20%, and lymphopenia in 16%. The researchers conclude that once daily administration of controlled-release carbimazole is effective with acceptable tolerance during short and long term treatment of feline hyperthyroidism. [SL]
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Related articles:
Frenais, R., S. Burgaud, and L.J.I. Horspool, Pharmacokinetics of controlled-release carbimazole tablets support once daily dosing in cats. Journal of Veterinary Pharmacology and Therapeutics, 2008. 31(3): p. 213-219.
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Trepanier, L.A., Medical management of hyperthyroidism. Clin Tech Small Anim Pract, 2006. 21(1): p. 22-8.
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Carbimazole for Feline Hyperthyroidism

Frenais, R., S. Burgaud, et al. (2008). "Pharmacokinetics of controlled-release carbimazole tablets support once daily dosing in cats." Journal of Veterinary Pharmacology and Therapeutics 31(3): 213-219.


Carbimazole is a common oral treatment for feline hyperthyroidism, although not in North America. Carbimazole is a prodrug, as it is converted to methimazole after metabolism. Methimazole reduces production of the thyroid hormones, T3 and T4. The pharmacokinetics of methimazole was investigated in healthy cats following oral administration of 15 mg of carbimazole as a newly available controlled-release tablet (Vidalta®, Intervet). Methimazole levels were sustained and without a peak when compared to dosing with conventional carbimazole tablets. Repeated oral dosing for 13 days did not lead to accumulation of methimazole in plasma. Absorption of carbimazole was improved when administered with food. The relative oral bioavailability of methimazole following administration of the controlled-release tablets was similar to that of a conventional release formulation (83 ± 21%). The pharmacokinetics of this controlled-release formulation of carbimazole supports its use as a once daily treatment (both as a starting dose and for maintenance therapy) for cats with hyperthyroidism.
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Related articles:
Bucknell, D. G. (2000). "Feline hyperthyroidism: spectrum of clinical presentions and response to carbimazole therapy." Aust Vet J 78(7): 462-5.
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