Development and validation of reversed phase liquid chromatographic method utilizing ultraviolet detection for quantification of irinotecan (CPT-11) and its active metabolite, SN-38, in rat plasma and bile samples: Application to pharmacokinetic studies

A new, simple, sensitive and specific reversed-phase high performance liquid chromatographic (HPLC) method using ultraviolet detection was developed and validated for the analysis of CPT-11 (λmax = 254 nm, 365 nm) and its major active metabolite, SN-38 (λmax = 380 nm) in rat plasma and bile. The sample pre-treatment from plasma involved a single protein precipitation step with cold acetonitrile. In case of bile, liquid–liquid extraction with dichloromethane: tert-butyl methyl ether (3:7) was carried out. Topotecan, a structurally related camptothecin, was used as an internal standard. An aliquot of 50 μL was injected onto a C-18 column. The chromatographic separation was achieved by gradient elution consisting of acetonitrile and water (pH 3.0 adjusted with 20% o-phosphoric acid) at a flow rate of 1.0 ml/min. Total run time for each sample was 30 min. All the analytes viz. topotecan, CPT-11, SN-38 were well separated with retention times of 11.4, 13.4 and 15.5 min, respectively. Method was found to be selective, linear (R2 ≈ 0.999), accurate (recovery ± 15%) and precise (<5% C.V.) in the selected concentration ranges for both the analytes. The quantification limit for CPT-11 was 40 ng ml−1 and for SN-38 was 25 ng ml−1. The percent extraction efficiency was ∼97% for CPT-11 and SN-38 from plasma while extraction recovery of CPT-11 and SN-38 from bile was ∼70% and ∼60%, respectively. The method was successfully used to determine plasma and biliary excretion time profiles of CPT-11 and SN-38, following oral and intravenous CPT-11 administration in rats. In the present study, irinotecan showed an absolute bioavailability of 30% as calculated from the pharmacokinetic data.