Carbimazole

Carbimazole: Uses, Dosage, and Side Effects

Overview

• Carbimazole is metabolized to the active drug methimazole, which interferes with the synthesis of thyroid hormones in a dose-dependent fashion.

Uses of Carbimazole

• Control of thyroid hormone levels in cats with hyperthyroidism.
• Carbimazole has also been used in canine hyperthyroidism but there are no data on the use of the sustained release formulation in dogs.

Dose of Carbimazole in Dogs and Cats

Dogs, Cats:

• Hyperthyroidism: starting dose 15 mg/animal p.o. q24h.
• Unless total thyroxine concentrations are <100 nmol (nanomoles)/l in which case starting dose is 10 mg p.o. q24h.
• Adjust dose in 5 mg increments but do not break tablets.

Side Effects of Carbimazole in Dogs and Cats

• Vomiting and inappetence/anorexia may be seen but are often transient.
• Jaundice, cytopenias, immune-mediated diseases and dermatological changes (pruritus, alopecia and self-induced trauma) are reported but rare.
• Treatment of hyperthyroidism can decrease glomerular filtration rate, thereby increasing serum urea and creatinine values, and can occasionally unmask occult renal failure.

Contraindications of Carbimazole in Dogs and Cats

Animals that have an adverse reaction to methimazole are likely also to have an adverse reaction to carbimazole.

Some Notes:

• Carbimazole should be discontinued before iodine-131 treatment.
• Do not use with low iodine prescription diets.