Liquid chromatography–electrospray tandem mass spectrometry method for determination of indapamide in serum for single/multiple dose bioequivalence studies of sustained release formulations

Indapamide and internal standard (5-chloro-2-methoxy-N-[2-(4-sulphamoylphenyl)ethyl]benzamide) were isolated from plasma by a single step liquid–liquid extraction in t-butyl methyl ether. The chromatographic separation was achieved on a reversed-phase C18 monolithic column with a mobile phase consisting in a methanol/aqueous 0.1% formic acid mixture and a flow rate of 0.8 ml/min, in isocratic conditions, within 11 min. Target compounds were transferred in an ion trap analyzer via an atmospheric pressure electrospray interface (AP-ESI). The mass analyzer was used in a selected reaction monitoring (SRM) mode, in order to enhance on detection selectivity. Whole method produces quantitation limit for indapamide of 1 ng/ml. Method was successfully applied to assess bioequivalence of two sustained release marketed pharmaceutical formulations of indapamide 1.5 mg coated tablets, carried-out in a single/multiple doses, randomized design.