A Novel UPLC-MS/MS Method for Detecting Simnotrelvir in Rat Plasma and Its Application for Pharmacokinetics

Simnotrelvir is a commonly used antiviral agent. In this study, we aimed to establish a novel UPLC-MS/MS method to quantitatively determine simnotrelvir in rat plasma and its application for pharmacokinetic research. Protein precipitation was used to prepare rat plasma. Gradient elution with a flow rate of 0.4 mL/min was applied for the separation of simnotrelvir and nirmatrelvir (internal standard) on a Waters ACQUITY UPLC BEH C18 column (1.7 μm, 2.1 × 50 mm). The mobile phase consisted of methanol and water. The mass transition pairs for nirmatrelvir and simnotrelvir were m/z 500.3 → 110.3 and m/z 550.20 → 160.15, respectively. In the bioanalytical method, it exhibited a good linearity (5-5000 ng/mL). The accuracy and precision ranged from -6.0% to 14.8% and 1.1% to 13.2%, respectively. The recovery and matrix effect of simnotrelvir were acceptable. Additionally, this analytical method was successfully used in pharmacokinetics in rats after oral administration. Pharmacokinetic parameters suggested that after oral administration, simnotrelvir reached the peak at 4.00 ± 1.10 h with a C_max value of 10376.02 ± 4301.78 ng/mL. The half-life of simnotrelvir was nearly 3 h. These results indicated that simnotrelvir was rapidly absorbed and cleared quickly in vivo.