Analysis of artesunic acid and dihydroqinghaosu in blood by high-performance liquid chromatography with reductive electrochemical detection.

A new high-performance liquid chromatography (HPLC) method using reductive electrochemical detection has been developed for the analysis of the antimalarial drugs artesunic acid (ARTS) and dihydroqinghaosu (DQHS) in blood. Presently, this method has been validated to 4 micrograms/ml for ARTS and 200 ng/ml for DQHS. Pharmacokinetic studies in the rabbit show that after intravenous administration (100 mg/kg) ARTS is metabolized rapidly to DQHS and has a t1/2 of 1.7 min in blood. DQHS data were fit to non-linear regression models consisting of the sum of two exponential terms. For phases 1 and 2, t1/2 values of 3.0 +/- 0.4 and 29 +/- 2 min were calculated, respectively. In vitro studies in which ARTS was incubated with blood from various species show that rabbit blood hydrolyzes ARTS at a much greater rate than rat or human blood. Incubation of ARTS with rabbit blood in the presence or absence of diisopropylfluorophosphate suggested that this hydrolysis reaction is catalyzed by plasma and red blood cell esterases. These results suggest that future pharmacokinetic studies in both animals and man should focus on the measurement of DQHS rather than ARTS.