Determination of paclitaxel and ritonavir in blood plasma and organs of rats by HPLC

Paclitaxel ( PTX ) is a cytotoxic antitumor agent from the taxane group, which low bioavailability and tissue biodistribution can be altered in the presence of inhibitors of liver enzymes and transport proteins. One of them is ritonavir ( RTV ), an antiretroviral agent used in the treatment of HIV infection. This study describes the development and validation of high-performance liquid chromatography with photodiode-array detection (HPLC-PDA) method for the simultaneous quantitative determination of PTX and RTV in rat blood plasma, liver, brain, and testis homogenates. Sample preparation involved liquid-liquid extraction followed by extract evaporation, redispersion in the mobile phase, and additional purification. Analytes were separated using LC-2030C 3D Plus Prominence-i system (Shimadzu) under reversed-phase chromatography conditions with an isocratic elution mode. The separation was performed on Hawach C18 Universal column (250 × 4.6 mm, 5 μm particle size). The mobile phase consisted of water (A) and acetonitrile (B) in a 50:50 ratio. Detection was carried out at the following wavelengths: for PTX 228 nm (retention time: 16 min), for RTV 240 nm (retention time: 19 min). The method demonstrated linearity over the concentration ranges of 100 – 9090 ng/mL PTX for plasma and 25 – 9090 ng/g for tissues, 250 – 9090 ng/g RTV in all matrices. The LOQs were 100 ng/mL PTX and 250 ng/mL RTV in plasma; 25 ng/g PTX and 250 ng/g RTV in tissues. The developed method exhibited high accuracy (relative error Δ < 12%) and precision (relative standard deviation RSD < 14%) across the entire concentration range. The recoveries for both PTX and RTV exceeded 80% in all biological matrices. In this regard, the method can be used to study the pharmacokinetics of this combination of drugs in biological matrices.