Mercazole5 mg

Mercazole 5 mg is indicated in the management of hyperthyroidism, thyrotoxicosis (including thyroid storm), and also for the preparation of patients for thyroidectomy. Mercazole 5 mg can also be used in combination with radio-active ablative therapy.

Anti-thyroid drugs

Mercazole 5 mg is metabolised to thiamazole which is responsible for its antithyroid action. It blocks the production of thyroid hormones through inhibition of the organification of iodide and the coupling of iodothyronine residues.

10 mg to 60 mg daily according to the severity of the disorder. The dose should be gradually reduced to the smallest amount which will control the disease. Daily dosage should be divided.

The initial dose: 20-60 mg, in 2-3 divided doses until the patient is euthyroid. Daily dosage should be divided.Maintenance regimen: The dose is gradually reduced to maintain a euthyroid state. The final dosage is usually in the range of 5-15 mg/day which may be taken as a single daily dose.Neonates & Children below 12 years: The usual initial dose is 250 mcg/Kg/day in divided doses.Duration of treatment: 18 to 24 months.

Mercazole 5 mg may interact adversely with other medicines. Iodine or iodine excess may decrease the response to Mercazole 5 mg, requiring an increase in dosage or longer duration of therapy with antithyroid agents. As thyroid and metabolic status of patient decreases toward normal, response to oral anticoagulants may decrease, however, if thioamide-induced hypoprothrombinemia occurs, anticoagulant effects may be enhanced. Adjustment of oral anticoagulant dosage on the basis of prothrombin time is recommended. Serum concentrations of digoxin and digitoxin have been reported to increase as the thyroid and metabolic status of patients taking antithyroid agents decreased, reduction in dosage of any digitalis glycoside may be necessary as patients become euthyroid.

Hypersensitivity to Mercazole 5 mg or other thiourea antithyroid agents.

Side-effects may include rash, pruritis, skin pigmentation, paraesthesias, urticaria, headache, arthralgia, and gastro-intestinal disturbances (including nausea, vomiting and gastric discomfort), and abnormal hair loss. Drug fever, a lupus-like syndrome, vasculitis and nephritis, and hepatic disorders, most commonly jaundice, and taste disturbances following Mercazole 5 mg therapy have been reported.

Pregnancy Category D. There is positive evidence of human foetal risk, but the benefits from use in pregnant women may be acceptable despite the risk

Mercazole 5 mg should be given with the utmost caution, or not at all, if there is any degree of tracheal obstruction, as high dosages may produce thyroid enlargement and obstructive symptoms may become marked.

Overdose or accidental poisoning may result in hypothyroidism and goitre. If blood dyscrasias occur, the drug should be immediately withdrawn. Further treatment is symptomatic and supportive.

Store below 25° C.

Anti-thyroid drugs

Mercazole 5 mg is an anti-thyroid substance which depresses the formation of thyroid hormone. It reduces the uptake and concentration of inorganic iodine by the thyroid but its main effect is to reduce the formation of di-iodotyrosine and thyroxine. Mercazole 5 mg is absorbed rapidly from the gastro-intestinal tract and is widely distributed throughout the body. Mercazole 5 mg is completely metabolised to methimazole and it is the metabolite that is responsible for its clinical activity. Mercazole 5 mg readily crosses the placental barrier and also attains a high concentration in the milk of lactating patients.

Mercazole 5 mg may be given during pregnancy to a thyrotoxic patient, but the smallest effective dose should be used an overdosage adversely affects the foetus. Mercazole 5 mg crosses the placenta and is excreted into breast milk. Mercazole 5 mg may, therefore, cause foetal or neonatal hypothyroidism and goitre.