Single daily dose of carbimazole in the treatment of hyperthyroidism

The antithyroid drugs, methimazole and carbimazole, are conventionally used in divided daily doses. However, these drugs have a longer intrathyroidal than a plasma half-life. We undertook this prospective, controlled study, in an area of mild iodine deficiency, to compare the efficacy of a single daily dose of carbimazole with divided doses in the treatment of hyperthyroidism.

Nineteen patients with hyperthyroidism received 30 mg of carbimazole daily at bed time (group A) while 14 received 10 mg of carbimazole every 8 hours (group B). These patients were assessed clinically and biochemically by estimation of serum total thyroxine, total triiodothyronine and thyrotropin before and 1, 2, 3, 4 and 6 weeks after treatment.

There was no significant difference between mean baseline concentrations of thyroxine and triiodothyronine. After 1, 2, 3, 4 and 6 weeks there was a decline in their concentrations which was similar in both groups (p > 0.05). Euthyroidism was achieved in 4.6 +/- 1.4 weeks (range 2-6 weeks) in group A and in 3.8 +/- 1.2 weeks (range 3-6 weeks) in group B (p > 0.05).

We conclude that carbimazole in a single daily dose is an effective method for treating hyperthyroidism in an area of mild iodine deficiency and its efficacy is comparable to divided dose therapy. This practical and acceptable method of treatment can be specially useful in patients who find it difficult to remember to take divided doses.