Orally administered
antithyroid drugs are frequently used to treat
hyperthyroidism in cats; however, the non-cooperative behaviour of some cats may make it difficult to administer
tablets. The aim of this study was to develop a
carbimazole ointment for application to the inner pinna of the ear and to test its effectiveness in 13 cats with
hyperthyroidism. Laboratory investigations were performed before, and 4, 8, and 12 weeks after start of the treatment. Laboratory data for 9 cats were available at the end of the observation period. The starting dose of
carbimazole ointment was 5 mg once daily. If no complications occurred, the dose was increased to 5 mg twice daily from the 6th day onwards. Further dose adjustments were mainly based on the plasma
thyroxine (T4) concentration. The median plasma T4 concentration at the end of the observation period (24 nmol/l) was significantly lower than that before treatment (152 nmol/l). The dosage of
carbimazole needed to achieve euthyroidism ranged from 4 to 17 mg twice daily. Treatment with
carbimazole ointment resulted in disappearance of signs of
hyperthyroidism; plasma concentrations of
urea and
creatinine increased significantly. The results of this study indicate that twice daily administration of
carbimazole ointment to the inner pinna of the ear is an effective treatment for
hyperthyroidism in cats. This provides the veterinarian with a new and promising treatment option. Because
carbimazole ointment has not been registered, according to European law it can only be used for the treatment of
hyperthyroidism in cats if other licensed medications have been tried and if there is a therapeutic need.