Determination of free ertapenem in plasma and bronchoalveolar lavage by high-performance liquid chromatography with ultraviolet detection

A sensitive assay for the determination of unbound ertapenem in human plasma and bronchoalveolar lavage (BAL) was developed using ultrafiltration of plasma and BAL samples. A rapid HPLC method was used with ultraviolet detection set at a wavelength of 305 nm and a separation on a Prontosil AQ C18 column, with imipenem used as internal standard. This assay was linear over the concentration range of 0.5-100 microg/mL and 0.25-50 microg/mL in plasma and BAL, respectively. Limits of detection and quantitation were respectively 0.05 and 0.25 microg/mL. Validation data for accuracy and precision were CV<2.48 and 8.25%, accuracy in the range 98.1-104.2% and 102.2-108.4%, respectively, for intra and inter-day.