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Date of issue: October 2022, Version: 4

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A corresponding patient information leaflet on USE OF METRONIDAZOLE IN PREGNANCY is available.

Metronidazole is an antimicrobial agent that is used for prophylaxis and treatment of anaerobic, protozoal, Helicobacter pylori and skin infections. It is commonly prescribed orally or as a gel for treatment of bacterial vaginosis and trichomonal infections. Where oral treatment is deemed appropriate, the manufacturer advises against a single high-dose regimen during pregnancy.

Metronidazole was teratogenic in some early animal studies, but this has proved difficult to reproduce. The available human data, which are almost exclusively based on oral exposure, do not, overall, indicate an increased risk of congenital malformation. There is also no indication of increased risks of preterm delivery, low infant birth weight, intrauterine death, or neonatal complications following metronidazole exposure in pregnancy. Metronidazole exposure in early pregnancy has been associated with miscarriage; however, it is possible that underlying maternal infection may play an independent role in increasing miscarriage risk.

Where possible, the results of culture and sensitivity tests should be available before making a treatment choice in accordance with local prescribing guidelines.

Exposure to metronidazole at any stage in pregnancy would not usually be regarded as medical grounds for termination of pregnancy or any additional fetal monitoring. However, other risk factors may 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.

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 NHS health care professionals who are logged in.

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 to ensure you are using the most up-to-date version.