Methima Mechanism of Action

Pharmacology: Pharmacodynamics: Methimazole inhibits the synthesis of thyroid hormones by blocking the oxidation of iodine in the thyroid gland. As a result, methimazole inhibits the ability of iodine to combine with tyrosine to form thyroxine (T₄) and triiodothyronine (T₃). It is effective in the treatment of hyperthyroidism. It does not inactivate existing thyroxine (T₄) and triiodothyronine (T₃), which are stored in the thyroid or which circulate in the blood.
Pharmacokinetics: Methimazole is rapidly absorbed from GI tract following oral administration with peak plasma concentrations occurring within about 1-2 hours. Onset of action is 12-18 hours. Methimazole readily crosses the placenta and is distributed into milk in concentrations approximately equal to those in maternal serum. This drug concentrated in thyroid gland. Protein binding of methimazole is 0%. Methimazole metabolized in the liver. The elimination half-life of methimazole reportedly ranges from about 5-13 hours. The drug is excreted in urine. In one study, about 12% of a dose was excreted in urine within 24 hours. Bioavailability of this drug is 80-95%.