Methamazole- Antithyroid drug

Methamazole

Methimazole (also known as Tapazole or Thiamazole or MMI) is an antithyroid drug,and part of the thioamide group. Like its counterpart propylthiouracil, a major side effect of treatment is agranulocytosis.

Indications

Methimazole is a drug used to treat hyperthyroidism, a condition that occurs when the thyroid gland begins to produce an excess of thyroid hormone. The drug may also be taken before thyroid surgery to lower thyroid hormone levels and minimize the effects of thyroid manipulation. Additionally, methimazole is used in the veterinary setting to treat hyperthyroidism in cats.

Mechanism of action

Methimazole inhibits the enzyme thyroperoxidase, which normally acts in thyroid hormone synthesis by oxidizing the anion iodide (I⁻) to iodine (I₂), hypoiodous acid (HOI), enzyme linked hypoiodate (EOI) facilitating iodine's addition to tyrosine residues on the hormone precursor thyroglobulin, a necessary step in the synthesis of triiodothyronine (T₃) and thyroxine (T₄).

It does not inhibit the action of the sodium-dependent iodide transporter located on follicular cells' basolateral membranes. Inhibition of this step requires competitive inhibitors such as perchlorate and thiocyanate.

Drug interactions

Adverse effects may occur for individuals who:

·         Take anticoagulants ('blood thinners') such as warfarin (Coumadin), diabetes medications, digoxin (Lanoxin), theophylline (Theobid, Theo-Dur), and vitamins

·         Have ever had any blood disease, such as decreased white blood cells (leukopenia), decreased platelets (thrombocytopenia) or aplastic anemia, or liver disease (hepatitis, jaundice)

·         Are pregnant, or going to become pregnant, or are breast-feeding.

Use of methimazole

Treating an overactive thyroid gland and treating or preparing the overactive thyroid gland for surgery. It may also be used when your doctor has advised against the removal of the thyroid. It may also be for other conditions as determined by your doctor.

Methimazole is an antithyroid agent. It works by inhibiting the production of thyroid hormone. Thyroid hormones are produced and released by the thyroid gland and regulate the body's metabolism.

Referance-Tripathi K.D,"Essentials of medical pharmacology",7th edition,page no-252,253