Determination of a new carbapenem antibiotic, DA-1131, in rat plasma, urine, and bile by column-switching high-performance liquid chromatography.

A column-switching high-performance liquid chromatographic method has been developed for the determination of a new carbapenem antibiotic, DA-1131, in rat plasma, urine, and bile. Each biological sample was diluted with an equal volume of a stabilizer, 3% KH2PO4 (containing 2.0% sodium citrate, adjusted to pH 6.0 with 10 M NaOH). After centrifugation for 1 min at 3000 g, an aliquot of the supernatant was injected directly onto the HPLC column. Deionized water was run for 3 min at a flow rate of 1.5 ml/min to retain DA-1131 in an extraction column, while proteins and endogenous interferences were eluted to the waste. The analyte was then back-flushed onto an analytical column, C18 reversed-phase column. The mobile phases for analytical column, 10 mM 3-[N-morpholino]propane sulfonic acid (pH 4.5)-acetonitrile (90:10, v/v) for plasma samples, and 5 mM KH2PO4 (adjusted to pH 8.0 with 10 M NaOH)-acetonitrile (90:10, v/v) for urine and bile samples, were run at a flow rate of 1.0 ml/min. The column effluent was monitored by ultraviolet detection at 300 nm. The retention time for DA-1131 was 8 min in plasma samples and 13 min for urine and bile samples. The detection limits for DA-1131 in rat plasma, urine, and bile were 0.05, 1.0, and 1.0 microgram/ml, respectively. The intraday and interday coefficients of variation of the assay were generally low (below 8.40%) for rat plasma, urine, and bile samples. No interference from endogenous substances was observed.