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MHRA drug safety update for carbimazole

Carbimazole, for Hyperthyroidism

The Medicines and Healthcare products Regulatory Agency (MHRA) have issued a drug safety update for the hyperthyroidism treatment carbimazole. The update states that cases of acute pancreatitis have been reported very infrequently during treatment with carbimazole

Acute pancreatitis is a condition where the pancreas becomes inflamed (swollen) over a short period of time.

The pancreas is a small organ, located behind the stomach, that helps with digestion.

Symptoms of acute pancreatitis include:
  • suddenly getting severe pain in the centre of your tummy (abdomen)
  • feeling or being sick
  • diarrhoea
  • a high temperature of 38C or more (fever)
The MHRA advice is:
  • if acute pancreatitis occurs, stop carbimazole treatment immediately
  • do not use carbimazole in patients with a history of acute pancreatitis in association with previous treatment
  • re-exposure may result in life-threatening acute pancreatitis with a decreased time to onset
  • report suspected adverse drug reactions to the Yellow Card Scheme immediately
For more information see full article.

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Carbimazole is authorised for use in the management of hyperthyroidism, including preparation for thyroidectomy and treatment before and after radioiodine treatment. Around 45,000–50,000 prescriptions for carbimazole a month are dispensed across GP practices in NHS England (data from

Carbimazole is a prodrug that undergoes rapid metabolism to the active metabolite, thiamazole. Thiamazole (synonym methimazole) is an antithyroid agent that acts by blocking the production of thyroid hormones. Thiamazole is not authorised for use in the UK.

Risk of acute pancreatitis
An EU review has found post-marketing reports of acute pancreatitis associated with the use of products containing carbimazole and thiamazole. In the UK, no Yellow Card reports of acute pancreatitis associated with carbimazole treatment have been received over a period of 55 years; however, a small number of reports have been received in other countries. Although the mechanism for development of acute pancreatitis is poorly understood, the presence of cases reporting recurrent acute pancreatitis with a decreased time to onset after re-exposure to carbimazole suggests a possible immunological mechanism.

Carbimazole must be immediately discontinued in patients who develop acute pancreatitis during treatment. Patients should be switched to an alternative therapy on the basis of an assessment of the individual benefits and risks.

Re-exposure to carbimazole must be avoided in patients who have previously experienced acute pancreatitis with carbimazole or thiamazole as re-exposure may result in recurrence of potentially life-threatening acute pancreatitis, with a decreased time to onset. The product information for products containing carbimazole is being updated to include risk of acute pancreatitis.

MHRA website
NHS website for acute pancreatitis
Contains public sector information licensed under the Open Government Licence v3.0.
Accessed 20/02/19
Links available in full article

MHRA information on carbimazole and risk of acute pancreatitis

Reporting of suspected adverse reactions

Reporting suspected adverse reactions (side effects) after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals or patients are asked to report any suspected adverse reactions via the Yellow Card Scheme at or search for MHRA Yellow Card in the Google Play or Apple App Store.

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