Indications

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

Composition

Pharmacology

Carbimazole 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. Carbimazole is absorbed rapidly from the gastro-intestinal tract and is widely distributed throughout the body. Carbimazole is completely metabolised to methimazole and it is the metabolite that is responsible for its clinical activity. Carbimazole readily crosses the placental barrier and also attains a high concentration in the milk of lactating patients.

Dosage & Administration

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.

Contraindications

Hypersensitivity to carbimazole or other thiourea antithyroid agents.

Side Effects

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 carbimazole therapy have been reported.

Pregnancy & Lactation

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

Precautions & Warnings

Carbimazole 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.

Therapeutic Class

Anti-thyroid drugs

Storage Conditions

Keep below 30°C temperature, away from light & moisture. Keep out of the reach of children.