Other safety alerts
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| The United Kingdom: Carbimazole: increased risk of congenital malformations; strengthened advice on contraception |
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Medicines and Healthcare products Regulatory Agency (MHRA) announces that carbimazole is associated with an increased risk of congenital malformations when used during pregnancy, particularly in the first trimester of pregnancy and at high doses (15 mg or more of carbimazole daily). 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.
Adequate treatment of hyperthyroidism in pregnant women prevents serious maternal and foetal complications. Carbimazole crosses the placental barrier and can cause foetal harm. An EU review of available evidence from epidemiological studies and case reports concluded there was evidence that carbimazole is associated with an increased risk of congenital malformations, especially when administered in the first trimester of pregnancy and at high doses (15 mg or more of carbimazole daily). Reported malformations include aplasia cutis congenita (absence of a portion of skin, often localised on the head), craniofacial malformations (choanal atresia; facial dysmorphism), defects of the abdominal wall and gastrointestinal tract (exomphalos, oesophageal atresia, omphalo-mesenteric duct anomaly), and ventricular septal defect.
The Patient Information Leaflet advises patients to tell their doctor straight away if they think they may be pregnant or are planning to have a baby. The use of carbimazole during pregnancy should be preserved for the situations in which a definitive therapy of the underlying disease (thyroidectomy or radioiodine treatment) was not suitable prior to pregnancy and in case of new occurrence or reoccurrence during pregnancy.
Healthcare professionals are advised:
- Carbimazole is associated with an increased risk of congenital malformations when used during pregnancy, particularly in the first trimester of pregnancy and at high doses (15 mg or more of carbimazole daily).
- Women of childbearing potential should use effective contraception during treatment with carbimazole.
- Carbimazole should only be considered in pregnancy after a thorough individual assessment of benefits and risks of treatment, and only at the lowest effective dose without additional administration of thyroid hormones; close maternal, foetal, and neonatal monitoring is recommended.
Please refer to the following website in MHRA for details:
http://www.gov.uk/drug-safety-update/carbimazole-increased-risk-of-congenital-malformations-strengthened-advice-on-contraception
In Hong Kong, there are 6 registered pharmaceutical products containing carbimazole, and 2 products containing methimazole. All products are prescription-only medicines. So far, the Department of Health (DH) has received one case of adverse drug reaction related to carbimazole, but this case is not related to congenital malformations. The DH has not received any case of adverse drug reaction related to methimazole. Congenital defects of carbimazole and methimazole have already been documented in overseas reputable drug references such as the “Martindale: The Complete Drug Reference”. The DH will remain vigilant on safety update of the drugs issued by other overseas drug regulatory authorities.
Ends/Tuesday, Feb 19, 2019
Issued at HKT 17:00
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