Quantitative liquid chromatography of allopurinol and oxypurinol in human plasma and urine

A high performance liquid chromatographic (HPLC) assay is described for allopurinol and oxypurinol determination in human plasma and urine, in the range expected during therapy. The procedure involves addition of trichloroacetic acid to samples, followed by centrifugation. The supernatant is then neutralized and analyzed by reversed-phase HPLC. Characteristics of the method are reported, and data are presented on its application to the pharmacokinetics studies. Separation is optimal with an octadecylsilane (ODS) stationary phase and a sodium acetate mobile phase adjusted to pH 7.2 for plasma and pH 5 for urine.