Determination of unbound ampicillin in rat blood by microdialysis and liquid chromatography

An in vivo microdialysis sampling method coupled to high-performance liquid chromatography has been applied for continuous monitoring of unbound ampic illin in rat blood. A microdialysis probe was inserted into the jugular vei n/right atrium of Sprague-Dawley rats, and doses of 100 and 200 mg/kg ampic illin were then administered via the femoral vein. Dialysates were collecte d and directly injected into a liquid chromatographic system. Isocratic elu tion of ampicillin was achieved within 10 min using the liquid chromatograp hic system. The chromatographic mobile phase consisted of methanol-100 mM m onosodium phosphoric acid (25.75, v/v, pH 5.5). The wavelength of the UV de tector was set at 230 nm. The calibration curves from 0.25 to 50 mug/ml wer e linear with correlation coefficients of 0.995. The method provides a simp le technique for rapid analysis of unbound ampicillin in rat blood for used in pharmacokinetic study.