Development and validation of a new RP-UPLC method for the simultaneous estimation of nirmatrelvir and ritonavir in bulk and copacked tablet dosage forms

The objective of this work is to develop a simple, accurate, precise and validated RP-UPLC method for effective simultaneous determination of nirmatrelvir and ritonavir in bulk and copacked tablet formulation. Separation of drugs was optimized after several trials by changing mobile phase composition, stationary phase, flow rate and column temperature. Finally the separation of drugs was achieved on a phenyl column (100 x 2.1 mm, 1.7 μ) using isocratic elution with a mobile phase of acetonitrile and triethyl amine (30:70 v/v). A flow rate of 0.5 mL/min. and a detector wavelength of 267 nm utilizing the PDA detector were given in the instrumental settings. Validation of the proposed method was carried out according to the International Council for Harmonization (ICH) guidelines. The system suitability parameters were within the limits, the retention time (Rt) for nirmatrelvir and ritonavir was achieved at 1.262 min. and 1.873 min. respectively over a total runtime of five minutes. The method showed linearity between the concentration range of 37.5-225 μg/mL for nirmatrelvir (R²; = 0.99956) and 25-150 μg/mL of ritonavir (R²; = 0.9998). The percentage recovery results by standard addition method for nirmatrelvir and ritonavir were found to be in the range of 99.3 % - 100.3 %. The proposed method is specific, accurate and robust. During stability tests, it can be used for routine analysis of the selected drugs.