Determination of unbound 20(S)-camptothecin in rat bile by on-line microdialysis coupled to microbore liquid chromatography with fluorescence detection

To evaluate the biliary excretion of unbound camptothecin, a flow-through microdialysis probe was constructed for bile sampling. The shunt linear probe was connected from the bile duct, between the liver side to the duodenum to avoid obstruction of the bile duct or bile salt waste. For automatic analysis of microdialysate, an on-line injector was connected to a microbore high-performance liquid chromatographic column with fluorescence detection. Samples were eluted with a mobile phase containing methanol-100 mM monosodium phosphoric acid (35:65, v/v, pH 2.5, adjusted with orthophosphoric acid). The limit of quantification was 1 ng/ml for camptothecin. Following camptothecin administration (5 mg/kg, i.v.), it was found in the bile microdialysate. It was concluded that the in vivo microdialysis technique yields useful data on the biliary excretion of camptothecin. This method is suitable for additional pharmacokinetic studies in rat bile.