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Date of issue: December 2021, Version: 1.0

Baloxavir marboxil is a Cap-dependent endonuclease inhibitor. It is used as a single-dose antiviral, licensed in the UK for post-exposure prophylaxis of influenza and in the treatment of uncomplicated influenza in patients aged 12 years or older.

Natural physiological and immunological adaptations result in pregnant women being at increased risk of severe influenza infection compared to the general population. Influenza infection in pregnancy carries increased risks of intensive care admission, preterm delivery, low birth weight, congenital anomalies, fetal demise and maternal death.

Although the manufacturer states that it is preferable to avoid the use of baloxavir during pregnancy, randomised controlled trials have shown single dose baloxavir treatment to have a similar efficacy as five days of oseltamivir treatment and to be associated with greater reductions in viral load and fewer adverse events. Baloxavir treatment may be of particular benefit to pregnant women with influenza, as they are at increased risk of developing severe disease. Preclinical animal models of exposure in pregnancy do not provide evidence of adverse embryo-fetal effects at doses up to five and seven times the human therapeutic dose respectively. The risk of harm from baloxavir in pregnancy is likely to be low given the animal model data, together with the therapeutic target for baloxavir being a virus specific enzyme. However, given that no human data are available, it is recommended that a cautious approach is taken and baloxavir use in pregnancy be reserved to clinical trial settings with careful collation of pregnancy outcome data.

Exposure to baloxavir 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.

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