High-pressure liquid chromatographic assay of cloxacillin in serum and urine

Two rapid, specific, and sensitive high-pressure liquid chromatographic (HPLC) assays were developed for cloxacillin in serum and urine. A reversed-phase column (RP-8) was selected for use with two different sets of HPLC conditions and sample pretreatment procedures. Cloxacillin extraction efficiencies are reported from serum and urine. Equations are presented for linear relationships between peak height or peak area ratios of cloxacillin to nafcillin (internal standard) and the cloxacillin concentration over a range of 0-80 micrograms/ml. The sensitivity limit of these assays was approximately 0.3 microgram/ml of a standard solution for one method and 0.05 microgram /ml for the other HPLC assay.