A Simple and Rapid LC-MS/MS Method for the Quantification of Nirmatrelvir/Ritonavir in Plasma of Patients with COVID-19.

The combined prescriptions of nirmatrelvir/ritonavir and other drugs are limited due to potential drug-drug interactions, so therapeutic drug monitoring (TDM) becomes particularly important. In this study, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was established for determination of the nirmatrelvir/ritonavir in plasma of patients with COVID-19, providing technical and theoretical support for the TDM. Plasma samples were processed by protein precipitation using acetonitrile, and analytes were separated on an Agilent Poroshell 120 SB-C18 (2.1 × 75 mm, 2.7  μ m) column at 35°C. Acetonitrile and 0.1% formic acid in water (52 : 48) were utilized as the mobile phases at a flow rate of 0.3 mL/min. In the multiple reaction monitoring (MRM) mode, nirmatrelvir and ritonavir were monitored using precursor/product ions: m / z 500.2/110.1 and 721.3/296.1, respectively, with selinexor as the internal standard. The linear range of both analytes was 2.0 ng/mL to 5000 ng/mL with good inter- and intraday precision and accuracy, and the recovery was 92.0%-107% for nirmatrelvir and 85.7%-106% for ritonavir. Finally, this method was successfully applied to monitor the exposure levels of nirmatrelvir/ritonavir in plasma samples from hemodialysis patients.