USE OF MOLNUPIRAVIR IN PREGNANCY
Date of issue: October 2025, Version: 2.0
Molnupiravir is an antiviral pro-drug that inhibits viral replication through the active metabolite being incorporated into the viral RNA, resulting in an accumulation of errors in the viral genome. In the UK, it is licensed as a five-day course for the treatment of mild-to-moderate COVID-19 in adults with a positive SARS-COV-2 diagnostic test who have at least one risk factor for developing severe illness.
Preclinical animal reproductive toxicity tests and experimental in vitro models have demonstrated embryotoxic and teratogenic effects of molnupiravir or its active metabolite. There are currently no data regarding the safety of molnupiravir in human pregnancy. UKTIS is collecting outcome data for all pregnancies with maternal or paternal exposure to molnupiravir (more information can be found here).
Although COVID-19 in pregnancy can present a significant risk to both the woman and her baby, the mechanism of action of molnupiravir and the preclinical animal data warrant a cautious approach towards its use in pregnancy. Molnupiravir is not routinely recommended in pregnancy. The manufacturer of molnupiravir recommends that women of childbearing potential should use effective contraception for the duration of treatment and for four days after the final dose. Pregnant women who have received molnupiravir at any stage of pregnancy should be referred to UKTIS for further counselling and follow-up of the pregnancy outcome.
In circumstances where a woman is experiencing severe symptoms of COVID-19, and where other more established treatments have failed, the risks and benefits of molnupiravir may need to be considered and discussed on an individual patient basis. However, the efficacy of molnupiravir has not been proven in such clinical scenarios, and alternative early treatment options that do not pose theoretical risks of fetal harm are preferred for pregnant women. Discussion with UKTIS is recommended in all cases where molnupiravir treatment is being considered in pregnancy.
Owing to the lack of data regarding malformation risks, routine detailed fetal anomaly scans are particularly recommended for pregnancies with exposure to molnupiravir in the first trimester, or where there was paternal exposure to molnupiravir around the time of conception. Exposure to molnupiravir at any stage in pregnancy would not usually be regarded as medical grounds for termination of pregnancy. 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.
Background
Molnupiravir is an antiviral pro-drug that is metabolised into ribonucleoside triphosphate which is subsequently incorporated into viral RNA, resulting in an accumulation of errors in the viral genome leading to inhibition of replication.[1]
Molnupiravir is licensed for the treatment of mild-to-moderate coronavirus disease 2019 (COVID-19) in adults with a positive SARS-COV-2 diagnostic test who have at least one risk factor for developing severe illness.[1] The product literature defines these risk factors as age 60 years or older, diabetes, obesity (BMI >30), chronic kidney disease, serious heart conditions, chronic obstructive pulmonary disease, or active cancer.[1] In non-pregnant high-risk populations, molnupiravir has been shown to be efficacious at reducing hospitalisation or death (as a composite outcome).[1] The standard dosing regimen involves a five-day treatment course.[1]
COVID-19 in pregnancy
Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection during pregnancy is known to increase the risk of adverse outcomes for both the woman and her baby. Women who are overweight or obese, 35 years old or older, of Black, Asian or any other minority ethnic background, or who have co-morbidities, such as diabetes, hypertension and asthma, are more likely to experience severe COVID-19.[2, 3] A meta-analysis conducted in 2020[2] indicated that approximately 10% of pregnant women with laboratory-confirmed COVID-19 are admitted to hospital, up to 7% require admission to intensive care units, and up to 5% require mechanical ventilation (more recent data have suggested these risks may be increased with newer SARS-CoV-2 variants[4]). Increased risks of preterm delivery, neonatal intensive care admission and stillbirth have also been described.[2] Due to a lack of up-to-date data, it is unclear whether COVID-19 infection in pregnancy continues to pose a high risk to the mother and fetus.
Preclinical (animal) data
Preclinical animal reproductive toxicity data are conflicting, with high maternal doses administered in the rat model demonstrating possible teratogenic effects but no evidence of similar effects observed in the rabbit model. However, experimental in vitro studies have demonstrated embryotoxic and possible teratogenic effects of molnupiravir or its active metabolite (NHC), using concentrations similar to those produced in human therapy.
Placental transfer of the NHC has been demonstrated in pregnant rats.[5] Pregnant rats administered doses of molnupiravir that produced active metabolite concentrations eight times those observed at the human recommended daily dose demonstrated post-implantation loss and offspring with malformations of the eye, kidney, axial skeleton, and rib variations. Reduced fetal body weight and delayed ossification was observed at doses equivalent to approximately three times the human recommended daily dose. It is noted that maternal toxicity was observed at the above doses. No developmental toxicity was observed at doses approximately 80% of those observed at the human recommended daily dose.[1] However, similar evidence of toxicity was not observed in the rabbit model, where doses equivalent to approximately seven times the human recommended daily dose were administered.[1]
Additional experimental preclinical models have also demonstrated embryotoxic and possible teratogenic effects of molnupiravir or NHC. At 28 hours post-fertilisation, transgenic zebrafish embryos (larvae) were incubated (10 embryos per well) with 0.04 micromole molnupiravir for 24 hours. The authors stated that the concentration used for the experiment aligned with the expected maximum plasma concentration observed in human therapy. At this exposure dose, altered swimming behaviour and decreased body size was observed in comparison with unexposed control embryos.[6] Mouse P19C5 stem cells incubated with 40 micromole molnupiravir or 20 micromole NHC reduced gastruloid growth and elongation. The authors stated that these concentrations approximated 1500 times and twice the maximum plasma concentration observed in human therapy, respectively. Similarly, human stem cells incubated with 10 micromole NHC reduced gastruloid growth and elongation, and gene expression changes were also observed at 2.5 micromole NHC. These NHC concentrations were comparable to plasma levels observed in humans following a clinical dose of molnupiravir.[7] Another preclinical model demonstrated that in vitro exposure of pre-implantation mouse embryos (>8 cell stage) with NHC resulted in blastocyst formation inhibition and caused extensive cell death at concentrations below the equivalent plasma concentrations produced in human therapy (from 0.2 micromole).[8] Although these models demonstrated adverse effects, they may be limited in their ability to predict risks in humans and the data should therefore be interpreted cautiously.
Human data
Often, data from observational sources or case reports, including data collected by UKTIS, may be confounded by maternal co-ingestion of a number of drugs, at varying doses, and for a range of indications. The severity of the underlying maternal condition, where relevant, is frequently unknown and information on other potential confounding variables may be incomplete. These factors should be considered when interpreting observational human pregnancy data.
There are currently no human data regarding the safety of molnupiravir in pregnancy. UKTIS is operating a registry to collect outcome data for all pregnancies with maternal or paternal exposure to molnupiravir (more information can be found here). NHS healthcare professionals are strongly encouraged to report such pregnancies to UKTIS.
Pharmacokinetic data
An ex vivo human cotyledon model suggested that there may be a low rate of placental transfer (4%) of NHC.[9] There are no in vivo data to confirm or refute this. No data regarding pregnancy-specific changes in the metabolism or pharmacokinetics of molnupiravir were located.
Miscarriage
Studies investigating relationships between gestational exposures and the occurrence of miscarriage should be interpreted with caution. Miscarriage prior to the recognition of pregnancy, or the pregnancy being reported to a clinician, is likely to be common; as such, observational studies likely underestimate true rates of early pregnancy loss. Additionally, the risk of miscarriage decreases as pregnancy progresses and elective termination acts as a competing risk. Correction for exposed and control group differences in stage of pregnancy at recruitment, and variation in the rate of elective termination, is therefore essential, but rarely performed.
No studies investigating the risk of miscarriage following maternal use of molnupiravir during pregnancy have been identified in the literature.
Congenital malformations/anomalies
No studies investigating the risk of congenital malformation following maternal use of molnupiravir during pregnancy have been identified in the literature.
Intrauterine death
No studies investigating the risk of intrauterine death/stillbirth following maternal use of molnupiravir during pregnancy have been identified in the literature.
Low birth weight/SGA
No studies investigating the risk of low birth weight following maternal use of molnupiravir during pregnancy have been identified in the literature.
Preterm delivery
No studies investigating the risk of preterm delivery following maternal use of molnupiravir during pregnancy have been identified in the literature.
Neonatal complications
No studies investigating the risk of neonatal complications following maternal use of molnupiravir during pregnancy have been identified in the literature.
Neurodevelopment
No studies investigating the risk of neurodevelopmental impairment following maternal use of molnupiravir during pregnancy have been identified in the literature.
Carcinogenicity
No studies investigating the risk of childhood cancer following maternal use of molnupiravir during pregnancy have been identified in the literature.
Paternal exposure
Only studies which examine the effects of paternal exposure on offspring congenital malformation rate, development, cancer and reproductive potential are included here. Effects on sperm quality and the reproductive health of the exposed father are NOT included.
There were no reports found regarding paternal exposure to molnupiravir. It is noted that there are no known human teratogens that affect fetal development via paternal exposure. However, both molnupiravir and its active metabolite have been observed to produce mutagenic effects in preclinical in vitro studies.[1] Although these results highlight some theoretical concerns regarding paternal molnupiravir exposure, reassuringly, mutagenic or genotoxic effects have not been observed in preclinical in vivo (rat) studies.[1] Mutagenic/genotoxic effects on sperm cell DNA are therefore unlikely following paternal molnupiravir use. Yet close monitoring of pregnancies fathered by those using molnupiravir at or around the time of conception remains warranted.
UKTIS is operating a registry to collect outcome data for all pregnancies with maternal or paternal exposure to molnupiravir (more information can be found here). NHS healthcare professionals are strongly encouraged to report such pregnancies to UKTIS.
Lactation
For information on the therapeutic use of medicines during breastfeeding, please consult the NHS UK Drugs in Lactation Advisory Service (UKDILAS) online lactation safety information (available from www.sps.nhs.uk) or contact the UKDILAS service directly (details can be found here).
If you have concerns regarding toxicity in the child as a consequence of exposure to a drug or chemical during lactation please consult TOXBASE or contact the National Poisons Information Service on 0344 892 0111.
UKTIS data
UKTIS have not followed up any cases of molnupiravir exposure during pregnancy.
Conclusions
Molnupiravir is not routinely recommended in pregnancy.
Although COVID-19 in pregnancy can present a significant risk to both the woman and her baby, both the mechanism of action of molnupiravir and the preclinical animal data warrant a cautious approach towards its use in pregnancy. The manufacturer of molnupiravir recommends that women of childbearing potential should use effective contraception for the duration of treatment and for four days after the final dose.
Pregnant women who have received molnupiravir at any stage of pregnancy should be referred to UKTIS for further counselling and follow-up of the pregnancy outcome.