A validated LC-MS/MS method for determination of antiviral prodrug molnupiravir in human plasma and its application for a pharmacokinetic modeling study in healthy Egyptian volunteers.

A fully validated, simple, rapid and reproducible liquid chromatography-tandem mass spectrometry method was developed to determine NHC (N-hydroxycytidine), the active metabolite of Molnupiravir (MOL) in human plasma; one of the limited treatment options for SARS-CoV-2 in plasma of healthy volunteers. The internal standard (IS) used was ribavirin. The extraction of analyte and IS from plasma was performed using acetonitrile as a solvent for protein precipitation. Agilent Zorbax Eclipse plus C, 4.6 × 150 mm, (5 µm) was used for chromatographic separation using a mixture of methanol0.2 % acetic acid (5:95, v/v) as a mobile phase that was pumped at a flow rate of 0.9 mL/min. Detection was performed on a triple quadrupole mass spectrometer operating in multiple reaction monitoring (MRM) employing positive ESI interface using API4500 triple quadrupole tandem mass spectrometer system, with the transitions set at m/z 260.10 → 128.10 and 245.10 → 113.20 for NHC and IS respectively. Method validation was performed in accordance with United States FDA bioanalytical guidance. The concentration range of 20.0-10000.0 ng/mL was used to establish linearity via weighted linear regression approach (1/x). Moreover, the analyzed pharmacokinetic data from twelve Egyptian healthy volunteers were used to develop a population pharmacokinetic model for NHC. The developed model was used to perform simulations and evaluate the current MOL dosing recommendations through calculating the maximum concentration (C) "the safety metric" and area under the curve (AUC) "the efficacy metric" for 1000 virtual subjects. Geometric mean ratios (GMR) with their associated 90% confidence intervals (CI) compared to literature values were computed. Geometric means of simulation-based Cmax and AUC0-12 were 3827 ng/mL (GMR = 1.05; 90% CI = 0.96-1.15) and 9320 ng.h/mL (GMR = 1.04; 90% CI = 0.97-1.11), respectively indicating that current MOL dosage can achieve the therapeutic targets and dose adjustment may not be required for the Egyptian population. The developed model could be used in the future to refine MOL dosage once further therapeutic targets are identified.