Development and validation of liquid chromatography–tandem mass spectrometric method for simultaneous determination of fosinopril and its active metabolite fosinoprilat in human plasma

A highly sensitive and selective liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed and validated for simultaneous determination of the prodrug fosinopril and its major active metabolite fosinoprilat for pharmacokinetic studies in healthy subjects. In order to get the lower limit of quantification (LLOQ), especially for analysis of fosinopril, key points of the method have been investigated including chromatographic conditions and selection of LC–MS/MS conditions. The analytes were extracted from plasma samples by liquid–liquid extraction, separated on a reversed-phase C8 column using gradient procedure, and detected by tandem mass spectrometry with a triple quadrupole ionization interface. The analytes and internal standard zaleplon were detected using positive electrospray ionization (ESI) in the SRM mode. The LLOQ of the method down to 0.1 ng mL−1 for fosinopril and 1.0 ng mL−1 for fosinoprilat were identifiable and reproducible. The standard calibration curves for both fosinopril and fosinoprilat were linear over the ranges of 0.1–15.0 and 1.0–700 ng mL−1 in human plasma, respectively. The within- and between-batch precisions (relative standard deviation (RSD)%) and the accuracy were acceptable. The validated method was successfully applied to reveal the pharmacokinetic properties of fosinopril and fosinoprilat after oral administration.