Quantitation of antibiotics by high-pressure liquid chromatography: cephalothin

A technique for quantitative determination of cephalothin and desacetylcephalothin in serum using a method based on high-pressure liquid chromatography is described. Both compounds were quantitatively extracted from serum by using dimethylformamide. After separation of the drugs by reverse-phase chromatography and detection by ultraviolet light absorption at 254 nm, serum concentrations of cephalothin and desacetylcephalothin as low as 1.0 mug/ml were measured. No interfering absorption was found in extracts of serum samples from normal humans or patients receiving a variety of other drugs, including other antimicrobial agents. Serum specimens obtained after an intravenous infusion of cephalothin to two human subjects and three dogs were assayed by the chemical and microbiological assays. When values, as determined by the chemical method and the microbiological assay in samples from human subjects, were compared, the correlation coefficient (r) was 0.96, whereas, in the dogs, the r value was 0.79. The chemical procedure described in this report for determination of cephalothin and desacetylcephalothin permits future pharmacokinetic investigations of these compounds. This assay is sensitive, specific, accurate, and rapid (approximately 30 min), and appears suitable for routine clinical use.