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(Date of issue: August 2018, Version: 2)

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 Aciclovir is available at


Aciclovir is an antiviral agent used systemically for the treatment of herpes simplex and varicella-zoster infections, or topically for herpes simplex infections of the skin, mucous membranes and eye. Valaciclovir, a prodrug of aciclovir, is used systemically in the treatment or prophylaxis of herpes simplex, varicella-zoster and cytomegalovirus infections.

Overall, the data do not suggest an increased risk of congenital malformation or other adverse fetal outcomes from exposure to either systemic aciclovir or valaciclovir or topical aciclovir at any time in pregnancy. However, outcomes other than congenital malformation have not been adequately studied to exclude an increased risk.

Human pregnancy data for valaciclovir are extremely limited but do not signal an increased malformation risk; other pregnancy and fetal outcomes have not been assessed. 

Aciclovir should be considered for all women presenting with a first episode of genital herpes during pregnancy. Daily use in the last four weeks of pregnancy to reduce the risk of recurrence and thus transmission to the neonate or need for caesarean section may also be considered. Pregnant women with chickenpox who present within 24 hours of rash onset should also be considered for aciclovir treatment.

In July 2018, Public Health England offered guidance in response to a national shortage of varicella zoster immunoglobulin, suggesting that immune naïve women with significant exposure to chickenpox or shingles after 20 weeks of pregnancy, should be offered aciclovir 800 mg QDS on days 7 to 14 post-exposure. Exposed women in the first 20 weeks of pregnancy should continue to be offered immunoglobulin therapy.

Exposure to aciclovir or valaciclovir 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 casespecific risk assessments.
This document is regularly reviewed and updated. Only use full UKTIS monographs downloaded directly from to be sure you are using the most up-to-date version. The summaries of these monographs are openly available on

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

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