High-pressure liquid chromatographic quantitation of azlocillin

We describe a rapid, precise, and simple procedure for the quantitation of azlocillin in serum and in aqueous solutions by high-pressure, reverse-phase liquid chromatography. This method uses a single precipitation step, detection by dual-wavelength monitoring (220 and 254 nm), and quantitation by comparison with an internal standard. The 10-micron C18 muBondapak column was eluted with 45% (vol/vol) methanol-65% (vol/vol) phosphate buffer. The precision was 4.2 and 5.6% at 50 and 10 micrograms/ml, respectively. The assay was linear up to concentrations of 100 micrograms/ml, with recoveries of 90.4 to 110.5% from serum. The assay was sensitive to 0.4 micrograms of azlocillin per ml. The short turnover time (14 min) and small serum sample size (20 microliters) make the assay ideal for therapeutic drug monitoring and clinical pharmacokinetic studies.