Merkastan - General Information
A thioureylene antithyroid agent that inhibits the formation of thyroid hormones by interfering with the incorporation of iodine into tyrosyl residues of thyroglobulin. This is done by interfering with the oxidation of iodide ion and iodotyrosyl groups through inhibition of the peroxidase enzyme. [PubChem]
Pharmacology of Merkastan
Used in the treatment of hyperthyroidism or an overactive thyroid gland, methimazole inhibits the synthesis of thyroid hormones and thus is effective in the treatment of hyperthyroidism. It may also be used to ameliorate hyperthyroidism in preparation for subtotal thyroidectomy or radioactive iodine therapy.
Merkastan for patients
Patients should be instructed to report to their physicians any symptoms of agranulocytosis, such as fever or sore throat.
Anticoagulants (oral): The activity of oral anticoagulants may be potentiated by anti-vitamin-K activity attributed to methimazole.
ß-adrenergic blocking agents: Hyperthyroidism may cause an increased clearance of beta ratio. A dose reduction of beta-adrenergic blockers may be needed when a hyperthyroid patient becomes euthyroid.
Digitalis glycosides: Serum digitalis levels may be increased when hyperthyroid patients on a stable digitalis glycoside regimen become euthyroid; reduced dosage of digitalis glycosides may be required.
Theophylline: Theophylline clearance may decrease when hyperthyroid patients on a stable theophylline regimen become euthyroid; a reduced dose of theophylline may be needed.
Tapazole is contraindicated in the presence of hypersensitivity to the drug and in nursing mothers because the drug is excreted in milk.
Additional information about Merkastan
Merkastan Indication: For the treatment of hyperthyroidism, goiter, Graves disease and psoriasis.
Mechanism Of Action: Merkastan binds to thyroid peroxidase and thereby inhibits the conversion of iodide to iodine. Thyroid peroxidase normally converts iodide to iodine (via hydrogen peroxide as a cofactor) and also catalyzes the incorporation of the resulting iodide molecule onto both the 3 and/or 5 positions of the phenol rings of tyrosines found in thyroglobulin. Thyroglobulin (Tg) is degraded to produce thyroxine (T4) and tri-iodothyronine (T3), which are the main hormones produced by the thyroid gland. So methimazole effectively inhibits the production of new thyroid hormones.
Drug Interactions: Anisindione The antithyroid agent causes variations in the anticoagulant effect
Warfarin The antithyroid agent causes variations in the anticoagulant effect
Dicumarol The antithyroid agent causes variations in the anticoagulant effect
Acenocoumarol The antithyroid agent causes variations in the anticoagulant effect
Digoxin The antithyroid agent increases the effect of digoxin
Food Interactions: Not Available
Generic Name: Methimazole
Synonyms: Thymidazole; Thymidazol; Thimazole; Thiamazole; Thiamazol; Metothyrine; Metothyrin; Methimazol; Methiamazole; Methamazole; Metazolo; Merkazolil; Mercazolyl; Mercazole; Mercasolyl; Mercaptazole
Drug Category: Antithyroid Agents
Drug Type: Small Molecule; Approved
Absorption: Rapid with an oral bioavailability of 93%.
Toxicity (Overdose): Oral LD50 in rats is 2250 mg/kg. Symptoms of overdose include nausea, vomiting, epigastric distress, headache, fever, joint pain, pruritus, and edema. Aplastic anemia (pancy-topenia) or agranulocytosis may be manifested in hours to days. Less frequent events are hepatitis, nephrotic syndrome, exfoliative dermatitis, neuropathies, and CNS stimulation or depression.
Protein Binding: None or minimal
Biotransformation: Primarily hepatic. Metabolized rapidly, requiring frequent administration.
Half Life: 5-6 hours
Dosage Forms of Merkastan: Tablet Oral
Chemical IUPAC Name: 1-methyl-3H-imidazole-2-thione
Chemical Formula: C4H6N2S
Methimazole on Wikipedia: https://en.wikipedia.org/wiki/Methimazole
Organisms Affected: Humans and other mammals