Background
Molnupiravir is an orally bioavailable prodrug of the nucleoside analogue β-D-N4-hydroxycytidine (NHC) and is used to treat coronavirus disease 2019 (COVID-19). However, the pharmacokinetics and transplacental transfer of molnupiravir in pregnant women are still not well understood. In the present study, we investigated the hypothesis that molnupiravir and NHC cross the blood-placenta barrier into the fetus.
Methods
A multisite microdialysis coupled with a validated ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC‒MS/MS) system was developed to monitor the dialysate levels of molnupiravir and NHC in maternal rat blood and conceptus (the collective term for the fetus, placenta, and amniotic fluid). Molnupiravir was administered intravenously (100 mg/kg, i.v.) on gestational day 16. To investigate the mechanism of transport of molnupiravir across the blood-placenta barrier, we coadministered nitrobenzylthioinosine (NBMPR, 10 mg/kg, i.v.) to inhibit equilibrative nucleoside transporter (ENT). Findings: We report that molnupiravir is rapidly metabolized to NHC and then rapidly transformed in the fetus, placenta, amniotic fluid, and maternal blood. Our pharmacokinetics analysis revealed that the area under the concentration curve (AUC) for the mother-to-fetus ratio (AUCfetus/AUCblood) of NHC was 0.29 ± 0.11. Further, we demonstrated that the transport of NHC in the placenta may not be subject to modulation by the ENT. Interpretation: Our