MHRA issues warning about use of carbimazole in pregnancy

In a Drug Safety Update, the Medicines and Healthcare products Regulatory Agency (MHRA) has issued a warning about the increased risk of congenital malformations with the use of carbimazole during pregnancy.

Carbimazole is a pro-drug that is rapidly metabolised to thiamazole, an anti-thyroid agent that suppresses the production of thyroid hormones. It licensed for the management of hyperthyroidism, including in preparation for thyroidectomy and as therapy prior to and after radioiodine treatment. The MHRA said an EU review of evidence from epidemiological studies and case reports showed that carbimazole is associated with an increased risk of congenital malformations when used during pregnancy, especially during the first trimester and at high dosages (≥15mg daily). The malformations that have been reported include aplasia cutis congenital, craniofacial malformations, defects of the abdominal wall and gastrointestinal tract, and ventricular septal defects.

Because of these risks, the MHRA advises that women of childbearing potential should use effective contraception during treatment with carbimazole, and directs users to the Faculty of Sexual and Reproductive Healthcare (FSRH) statement on contraception for women using teratogenic drugs. In addition, carbimazole must only be used in pregnancy when clinically indicated, after a strict individual assessment of the benefits versus risks, and only at the lowest effective dose without additional administration of thyroid hormones. Use should be reserved for situations in which a definitive therapy of the underlying disease (ie thyroidectomy or radioiodine treatment) was not suitable prior to pregnancy and in cases of new occurrence or reoccurrence during pregnancy. The MHRA also recommends close maternal, foetal and neonatal monitoring if carbimazole treatment is required.

In a separate Drug Safety Update, the MHRA has also warned about a small risk of acute pancreatitis during treatment with carbimazole. Although there have been no UK Yellow Card reports, an EU review found a small number of post-marketing reports of acute pancreatitis associated with the use of products containing carbimazole or thiamazole. The MHRA therefore advises that carbimazole treatment should be stopped immediately and permanently if acute pancreatitis occurs. Re-exposure must be avoided in patients with a history of acute pancreatitis in association with previous treatment, because of the risk of life-threatening acute pancreatitis with a decreased time to onset.

As usual, any suspected adverse drug reactions should be reported via the Yellow Card Scheme.


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