Carbimazole

Uses

Carbimazole is used for 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

Carbimazole is also used to associated treatment for these conditions: Hyperthyroidism

How Carbimazole works

Carbimazole is an aitithyroid agent that decreases the uptake and concentration of inorganic iodine by thyroid, it also reduces the formation of di-iodotyrosine and thyroxine. Once converted to its active form of methimazole, it prevents the thyroid peroxidase enzyme from coupling and iodinating the tyrosine residues on thyroglobulin, hence reducing the production of the thyroid hormones T3 and T4.

Dosage

Carbimazole dosage

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.

Side Effects

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.

Precaution

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

Interaction

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.

Pregnancy & Breastfeeding use

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

Contraindication

Hypersensitivity to carbimazole or other thiourea antithyroid agents

Acute Overdose

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.

Storage Condition

Store below 25° C.

Innovators Monograph

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