Carbimazole

Carbimazole is used to treat hyperthyroidism. Carbimazole is a pro-drug as after absorption it is converted to the active form, methimazole. Methimazole prevents thyroid peroxidase enzyme from coupling and iodinating the tyrosine residues on thyroglobulin, hence reducing the production of the thyroid hormones T₃ and T₄ (thyroxine).

Clinical use

Therapy for hyperthyroidism generally starts at a high daily dose of 15–40 mg continued until the patient has normal thyroid function, and then reduced to a maintenance dose of 5–15 mg. Treatment is usually given for 12–18 months followed by a trial withdraw.

The onset of anti-thyroid effect is rapid but the onset of clinical effects on thyroid hormone levels in the blood is much slower. This is because the large store of pre-formed T₃ and T₄ in the thyroid gland and bound to thyroid binding globulin (99% bound) has to be depleted before any beneficial clinical effect occurs.

Precautions

Some people are allergic to azole(s). Some azole drugs have adverse side-effects. Some azole drugs may disrupt estrogen production in pregnancy, affecting pregnancy outcome.