Carbizol

• Thyrotoxicosis

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

N/A

Hypersensitivity to carbimazole or other thiourea antithyroid agents

Carbimazole 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.

Carbimazole may interact adversely with other medicines. Iodine or iodine excess may decrease the response to Carbimazole, 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.

Nausea, headache, arthralgia, fever, jaundice, malaise, mild gastric distress, skin rashes, pruritus, taste disturbance; bone marrow depression including neutropenia, eosinophilia, leucopenia. Rarely, pancytopenia/aplastic anaemia and isolated thrombocytopenia, haemolytic anaemia.

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 If blood dyscrasias occur, the drug should be immediately withdrawn.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.

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

Caution should be taken in patients with intrathoracic goitre. Mild to moderate hepatic impairment. Caution also should be taken in children, pregnancy and lactation.