Rapid RP-HPLC-UV determination of molnupiravir, nirmatrelvir, and remdesivir alone, in pharmaceutical mixture and plasma

Molnupiravir, nirmatrelvir, and remdesivir are antiviral drugs used in the latest COVID-19 treatment protocols. The proposed method describes a simple, sensitive, and accurate reversed-phase high-performance liquid chromatography (RP-HPLC-UV) for estimating these pharmaceuticals individually or in mixtures within their combined or individual pharmaceutical formulations. The method separates the mixture using a Nova-Pak® CN (HP 150 mm × 3.9 mm, 4 μm) analytical column and a gradient mobile phase of 50 mM ammonium acetate and methanol. The flow rate is 1.00 mL/min, the detector wavelength is set at 230 nm, and the column temperature is maintained at 30 °C, retention times observed were 2.03, 4.74, and 5.51 min. The method demonstrated linearity over ranges of 2–30, 15–225, and 5–75 µg/mL for molnupiravir, nirmatrelvir, and remdesivir, respectively, with correlation coefficients greater than 0.999. The validation method met the ICH Q2(R2) criteria, confirming its suitability for analyzing raw materials pharmaceutical dosage forms. The method was successfully applied to determination of these antivirals in human plasma samples, using a two-stage extraction procedure, demonstrating its utility for therapeutic drug monitoring.