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 (Paxlovid) and other drugs are limited due to potential interaction, 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 μm) column at 35°C. Acetonitrile and 0.1% formic acid in water (52:48, V:V) was utilized as the mobile phases at a flow rate of 0.3 mL/min. In 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 internal standard. The linear range of both analytes was 2.0-5000.0 ng/mL with good intra-and intra-day precision and accuracy, and the recovery was 91.95%-106.67% for nirmatrelvir, and 85.72%-105.84% for ritonavir. Finally, this method was successfully applied to monitor the exposure levels of nirmatrelvir/ritonavir in plasma samples from hemodialysis patients.