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This medicine is also supplied under the trade name Neo Mercazoleâ and is available as:
Tablets containing carbimazole 5 mg and 20 mg.

How does it work?

Carbimazole is converted in the body to the active agent, methimazole which acts on the thyroid to reduce overactivity.

Treatment is started at high dosage often 20-60mg per day taken as 2-3 divided dosages and is maintained until the patient’s thyroid returns to normal activity. Subsequent therapy may then be given in one of two ways.

1. Maintenance Regimen The dosage is gradually decreased so as to maintain normal thyroid activity. This maintenance dosage can vary from patient to patient in the range 5-15mg per day which may be taken as a single daily dosage. Therapy is usually continued for 12-18 months.

2. Block-replacement regimen In some the dosage is maintained at the initial high level (i.e. 20-60mg per day) and supplemental thyroxine (50-150mcg per day) is also given in order to prevent an underactive thyroid induced by the high dosage of carbimazole. Therapy is continued for 12-18 months.

Adverse reactions if they occur usually are seen in the first 8 weeks of treatment.

• Headaches, nausea, joint pains, stomach upset.
• Skin rashes are common in possibly 1 in 50 patients. If it occurs cease the drug and contact your doctor.
• A rare side effect is bone marrow depression which can present in 1 in 1000 patients. This presents as a severe sore throat, mouth ulcers, fever. If it occurs cease the drug and contact your doctor immediately. The suppression of the bone marrow is often temporary with the bone marrow recovering after 1-2 week.

Carbimazole is used in pregnancy but the specialist will aim to use the lowest dosage possible and will not use the drug combined with thyroxine. The reason for this is that carbimazole does cross the placenta into the baby so the lowest dosage is preferred. There have been rare instances of babies born with nail/finger abnormalities (aplasia cutis) while on carbimazole but whether the drug is the cause has lately been thought by some not to be the case.

Carbimazole does enter mother’s milk and although this does not preclude breast feeding it is essential that baby is closely monitored and the lowest effective dose is used. Some for safety reasons advise no breast feeding.

Carbimazole tablets should be stored at room temperature. Keep in the original container in which they have been dispensed and protect from direct sunlight.

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Ó NHS Tayside; 2006; version 1.0

Disclaimer; no liability whatsoever is accepted for information given and all such information, especially with regard to drug usage (UK version provided), must be checked with a person’s health provider.