A validated LC-MS/MS method for determination of Molnupiravir and Favipiravir in human plasma; Assessment of the remarkable potential synergistic effect against SARS-CoV-2 Infection: Application to a pharmacokinetic study in healthy Egyptian volunteers

Several clinical trials were carried out to find the route for an efficient therapy against SARS-CoV-2 infection. Mono- and dual therapy of various antivirals were investigated and found to have a clinical benefit in infected patients. Some of these antivirals are Molnupiravir (MOL) and Favipiravir (FAV), both drugs were evaluated for combined antiviral activity in some recent clinical trials. In this study, an efficient, simple, and rapid LC-MS/MS method for simultaneous determination of N-hydroxycytidine (NHC), MOL active metabolite, and FAV in human plasma of healthy volunteers was developed. Plasma protein precipitation was performed using acetonitrile. Compounds' separation was achieved using Agilent Zorbax Eclipse plus C18, 4.6 x 150 mm, 3.5 mu m and an isocratic elution of a mobile phase composed of methanol - 0.2 % acetic acid (10:90, v/v) at a flow rate of 0.5 mL/min using pyrazinamide as an internal standard (IS). Drugs were quantified using API 6500 + Qtrap mass spectrometer employing a selective ion mode combining a positive and negative ESI interface. The bioanalytical method was validated in accordance with the US-FDA bioanalytical guidance. The calibration range for both NHC and FAV was 10.0-10000.0 ng/mL computed via weighted linear regression approach (1/x2). The proposed method could be applied to support the upcoming clinical studies for therapeutic drug monitoring of patients undergoing dual combination therapy as the latter combination proved more efficacious and powerful tool for the complete treatment of SARS-CoV-2 cases. Finally, the suggested bioanalytical method was efficiently utilized in human pharmacokinetic study of NHC and FAV, after simultaneous co-administration, in healthy volunteers.