Methimazole

Mechanism :

Methimazole is an anti-thyroid drug that inhibits the uptake of iodine by the thyroid gland. It is used in patients who have hyperthyroidism. It is more potent and has a longer duration of action than propylthiouracil.

Indication :

• To control thyrotoxicosis in Grave’s disease and Toxic Nodular Goitre as definitive therapy, pre-operatively and along with radioactive iodine. Contraindicated in pregnant women and lactating mothers because it crosses the placenta and passes in the breast milk causing hypothyroidism in the fetus and the infant respectively.

Contraindications :

Hypersensitivity Reactions, Breastfeeding.

Caution if pregnancy, myelosuppression, agranulocytosis hepatic impairment.

Dosing :

Adverse Effect :

Hypothyroidism, agranulocytosis, aplastic anemia, thrombocytopenia, rash, pruritus, skin pigmentation, urticaria, alopecia, neuritis, polyarthritis, salivary gland swelling, vertigo, leukocytoclastic vasculitis, hepatotoxicity.

Interaction :

Acenocoumarol: The antithyroid agent, methimazole, may decrease the anticoagulant effect of acenocoumarol.
Anisindione: The antithyroid agent, methimazole, may decrease the anticoagulant effect of anisindione.
Dicoumarol: The antithyroid agent, methimazole, may decrease the anticoagulant effect of dicumarol.
Digoxin: The antithyroid agent increases the effect of digoxin.
Tamoxifen: Methimazole may decrease the therapeutic effect of Tamoxifen by decreasing the production of active metabolites. Consider alternate therapy.
Tamsulosin: Methimazole, a CYP2D6 inhibitor, may decrease the metabolism and clearance of Tamsulosin, a CYP2D6 substrate. Monitor for changes in therapeutic/adverse effects of Tamsulosin if Methimazole is initiated, discontinued, or dose changed.
Warfarin: Methimazole may decrease the anticoagulant effect of warfarin. Monitor for changes in the therapeutic and adverse effects of warfarin if methimazole is initiated, discontinued or dose changed.

Hepatic Dose :