Abstract: 4-4″-(2″,2″,6″,6″-tetramethyl-1″-piperidinyloxy)amino-4'-demethylepipo-dophyllotoxin (GP-7) is a new podophyllotoxin spin-labeled derivative.Its primary effect is theantitumor activity on transplanted mouse tumors and cultured tumor cells. This paper describes amethod for its determination using HPLC with UV detection and the determination of itspharmacokinetic parameters in rats.A Shimadzu LC-6A liquid chromatograph equipped with a Shimadzu SPD-6AV multiwavelengthdetector and a Chromatopac C-R3A data processor was used.The separation was performed on aZorbax-ODS column(5μm,4.6 mm×150 mm) with a mobile phase of methanol-water-glacialacetic acid(59:41:0.6).The flow-rate was 1.0 ml· min^-1 and detection was made at 285 nm.A plasma specimen(0.2 ml) was spiked with 22.6μg· ml^-1 internal standard(podophyllic acidpiperidinyl hydrazone nitroxide radical, GP-1) and extracted with ether-dichloromethane(3:1).The extract was evaporated at 45℃. The residue was taken up with 0.1 ml of the mobile phase and20μl aliquots were injected into the system.The calibration curve was linear in the range from 2 to 200μg·ml^-1 with r=0.9997. Thedetection limit was 0.2 μg· ml^-1 and the recovery of GP-7 from rat plasma was 94.3%～100.9%.The relative standard deviations for within-day and between-day were 2.29%～4.64%and5.55%～7.70%, respectively.After iv injection of GP-7 10,20 and 30 mg· kg^-1,the concentrations of the drug in ratplasma were determined.The pharmacokinetic parameters of GP-7 were obtained by using MCPKPprogram on a COMPAC-486 computer. The data obtained fitted a two-compartment open model, andthe mean T1/2βvalue was 39.8±10.8 min.