Determination of ampicillin, amoxicillin, cephalexin, and cephradine in plasma by high-performance liquid chromatography using fluorometric detection.

Several methods for the assay of aminopenicillins [l-8] and aminocephalosporins [g-16] in the body fluids have been studied. These utilize techniques such as fluorometory [l-6, 9-12] and high-performance liquid chromatography with UV detection [7, 8, X3-16]. These methods including our methods, however, are not sufficient for concentrations below about 50 ng/ml of plasma. And in the case of the experiments which study intestinal absorption behavior of these drugs, a more sensitive method of determination in the body fluids is required. Recently, Uno et al. [17], Lebelle et al. [18], and Rarbhaiya et al. [19] showed that the structure of the fluorescent degradation products employed in some fluorometric assay procedures, including products obtained by our procedures, had a pyrazine‘ ring as a common structural unit. In this study, we have developed a more sensitive and a reproducible high-performance liquid chromatographic (HPLC) assay for ampicillin, amoxicillin, cephalexin, and cephradine based on the common structure of these fluorescent degradation products obtained by our previous assay procedures.