Concurrent determination of topotecan and model permeability markers (atenolol, antipyrine, propranolol and furosemide) by reversed phase liquid chromatography: utility in Caco-2 intestinal absorption studies.

A simple, sensitive, specific and high-resolution reversed-phase liquid chromatographic method utilizing ultraviolet detection has been developed and validated for simultaneous determination of topotecan and four intestinal permeability markers (atenolol, antipyrine, propranolol and furosemide) as suggested by US-FDA. Chromatography was carried out on C-18 column with mobile phase comprising water (pH 3.0) and acetonitrile gradient pumped at a flow rate of 1 ml min(-1). The validation parameters included specificity, accuracy, precision, sensitivity and stability studies. Topotecan, an anti-cancer drug widely used in metastatic carcinoma, is a P-glycoprotein substrate having oral bioavailability of 30% with large inter-patient variability. The present method was successfully applied for demonstrating P-gp mediated transport of topotecan and its inhibition using verapamil in Caco-2 cell monolayer. The method can be used in identification of novel P-gp inhibitors for topotecan and estimating the contribution of P-gp in affecting oral bioavailability of topotecan. The other applications of method include its use in validation of Caco-2 monolayer assay for getting biowaiver based on Biopharmaceutic Classification System and its extrapolation to in situ and/or in vivo studies.