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USE OF AZATHIOPRINE OR MERCAPTOPURINE IN PREGNANCY

Date of issue: December 2019
Version: 3

This is a UKTIS monograph for use by health care professionals. For case-specific advice please contact UKTIS on 0344 892 0909. To report an exposure please download and complete a pregnancy reporting form. Please encourage all women to complete an online reporting form.

A corresponding patient information leaflet on azathioprine or mercaptopurine use in pregnancy is available at www.medicinesinpregnancy.org.

Summary

Azathioprine is a prodrug and is rapidly metabolised to its active metabolite mercaptopurine (6-MP). Mercaptopurine is a purine analogue which interferes with the synthesis of DNA and RNA and has immunosuppressant properties. Azathioprine is licensed to treat various auto-immune disorders such as inflammatory bowel disease, rheumatoid arthritis and psoriasis, and for the prevention of allograft rejection. It is also used off-licence to treat severe refractory eczema. Mercaptopurine is licensed to treat acute and chronic leukaemia, as maintenance therapy in acute lymphoblastic and myelogenous leukaemia, and is used off-license to treat severe ulcerative colitis and Crohn’s disease.

The available data do not demonstrate that azathioprine/mercaptopurine exposure during early pregnancy increases the risk of congenital malformation, preterm delivery, or adversely affects fetal growth. There is also no robust evidence of increased risks of intrauterine death, miscarriage, or altered neurodevelopment following gestational azathioprine exposure. However, as the available data for many of these outcomes are limited in quantity and sometimes also methodologically, more robust epidemiological data are ideally required.

Neonatal leucopoenia and thrombocytopenia have been reported in a number of case reports following azathioprine exposure in utero but no epidemiological studies quantifying these risks are available. There is therefore a theoretical concern that the use of azathioprine/mercaptopurine during pregnancy could result in immunosuppression in the neonate, leading to an increased risk of infection and adverse effects following administration of live vaccines. Advice from the MHRA states that infants exposed in utero to certain immunosuppressive medications should not receive live vaccines until they are least 6 months old, although no specific advice relating to azathioprine exposure was issued.

This document is regularly reviewed and updated. Only use full UKTIS monographs downloaded directly from TOXBASE.org to be sure you are using the most up-to-date version. The summaries of these monographs are openly available on UKTIS.org

This is a summary of the full UKTIS monograph for health care professionals and should not be used in isolation. The full UKTIS monograph and access to any hyperlinked related documents is available to health care professionals at www.toxbase.org.

If you have a patient with exposure to a drug or chemical and require assistance in making a patient-specific risk assessment, please telephone UKTIS on 0344 892 0909 to discuss the case with a teratology specialist.

If you would like to report a pregnancy to UKTIS please click here to download our pregnancy reporting form. Please encourage all women to complete an online reporting form.

Disclaimer: Every effort has been made to ensure that this monograph was accurate and up-to-date at the time of writing, however it cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes of the measures recommended. The final decision regarding which treatment is used for an individual patient remains the clinical responsibility of the prescriber. This material may be freely reproduced for education and not for profit purposes within the UK National Health Service, however no linking to this website or reproduction by or for commercial organisations is permitted without the express written permission of this service. This document is regularly reviewed and updated. Only use UKTIS monographs downloaded directly from TOXBASE.org or UKTIS.org to ensure you are using the most up-to-date version.