Clinical efficacy and safety of a once-daily formulation of carbimazole in cats with hyperthyroidism

Objective Evaluation of efficacy and safety of a novel controlled-release formulation of carbimazole in feline hyperthyroidism. Methods A multicentre, self-controlled study in 44 client-owned cats with history and clinical signs of hyperthyroidism, and total thyroxine concentration greater than or equal to 50 nmol/l. Treatment was started at 15 mg once daily, response assessed after 10 days, and 3, 5, 8, 26 and 53 weeks and dose adjusted as required. Results The median dose of carbimazole was 10 mg (range 10 to 15 mg) and 15 mg (5 to 25 mg) once daily after 3 and 53 weeks, respectively. Median total thyroxine concentration dropped significantly from 118 nmol/l (50 to 320 nmol/l) at presentation to 33 nmol/l (n=40) after 10 days, 31 nmol/l (n=34) at 3 weeks and 21 nmol/l (n=18) at 53 weeks. Clinical signs improved or resolved in almost all cats within three weeks after starting treatment. Twenty-one adverse reactions possibly (20) or probably (1) related to treatment were reported. During treatment, increased blood urea nitrogen concentration was observed in 25 per cent of the cats, eosinophilia in 20 per cent and lymphopenia in 16 per cent, while liver enzymes tended to improve. Clinical Significance Once daily administration of controlled-release carbimazole tablets was effective and had expected tolerance in hyperthyroid cats during short- and long-term treatment.