Endocrine Abstracts (2019) 65 P443 | DOI: 10.1530/endoabs.65.P443

The need to update patient safety information on carbimazole

Vera Smout & Jennifer Tringham


Frimley Park Hospital, Frimley, UK


Hyperthyroidism commonly affects women of child-bearing age. Use of carbimazole in the first trimester of pregnancy has been shown to be associated with certain congenital abnormalities, such as aplasia cutis, choanal atresia, dysmorphic facial features, abdominal wall and gastrointestinal tract defects, in up to 2% of cases. The MHRA issued a Drug Safety Alert in February 2019, recommending to strengthen the advice on contraception given to women of child-bearing age who need treatment with carbimazole, particularly at a dose above 15 mg a day. In the Endocrinology Department at Frimley Park Hospital, we have adapted our practice with the aim that contraception and plans for pregnancy will be discussed with all female patients of child-bearing age. We addition, we reviewed the Trust patient information leaflet on anti-thyroid medication, which had previously not mentioned the use of carbimazole in pregnancy. We studied the available literature on the topic and added a section to our leaflet discussing the risks of congenital malformations linked to carbimazole. We have included advice on using effective contraception while taking the medication and recommendations to discuss switching to propylthiouracil in the event of pregnancy or if planning a pregnancy, as this is considered safer in the first trimester. We aim to reduce the risk of teratogenic effects of carbimazole in the first trimester of pregnancy by ensuring our patients are better informed about the medication, the need for effective contraception and when to seek advice regarding their management.

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