USE OF MEFENAMIC ACID IN PREGNANCY

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(Date of issue: March 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 mefenamic acid use in pregnancy is available at www.medicinesinpregnancy.org.

Summary

Mefenamic acid is a non-steroidal anti-inflammatory drug (NSAID) used to treat acute and chronic pain (particularly dysmenorrhoea) and in the management of rheumatoid arthritis. 

Use of NSAIDs in pregnancy has been associated with an increased risk of miscarriage, persistent pulmonary hypertension of the newborn (PPHN), oligohydramnios, premature closure of the ductus arteriosus (DA), structural cardiovascular defects and a number of other congenital anomalies, including orofacial clefts. However the available data are limited, confounded and often conflicting; further research is therefore required to define the risk of these outcomes more accurately.

Published data concerning the safety of maternal mefenamic acid use in human pregnancy are limited to a single placebo-controlled randomised clinical trial which investigated mefenamic acid as a tocolytic in late pregnancy. No adverse fetal effects were observed in this study and women receiving mefenamic acid were less likely to deliver preterm than those treated with placebo. However, this study did not provide data concerning the safety of mefenamic acid use in early pregnancy and the study sample was small. Published data are too limited to provide an adequate assessment of the safety of mefenamic acid use in pregnancy.

Exposure to NSAIDs after 30 weeks of gestation has been associated with an increased risk of premature closure of the DA and oligohydramnios. These effects are thought to be mediated by the inhibitory effect of NSAIDs on prostaglandin production. There are conflicting findings regarding the risks of PPHN following antenatal use of NSAIDs. Further evidence is required before this possible association can be confirmed. Where published data concerning the fetal effects of gestational exposure are unavailable or limited, a possible class effect for these associations should be considered for all NSAIDs.

All NSAIDs should, where possible, be avoided during the third trimester. In circumstances where the maternal clinical condition requires treatment with mefenamic acid during the third trimester, discussion with a Fetal Medicine Unit regarding antenatal monitoring for oligohydramnios and ductus arteriosus patency is recommended. Where use of mefenamic acid is being considered at any stage of pregnancy the available pregnancy data should be discussed with the patient to support informed decision-making regarding the risks and benefits of treatment.

Please refer to the NSAID overview monograph for more information. Other risk factors may also be present in individual cases which may independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments. Discussion with UKTIS is recommended for all cases of mefenamic acid exposure in pregnancy.

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.