HPLC analysis of metabolites isolated from urine of a normal subject taking naproxen.

The 6-0-desmethyl naproxen and naproxen standards had retention times of 9.9 and 12.1 minutes, respectively (dashed peaks). Retention time of the major urinary peak (solid line) was 10.3 minutes, which was identical to the retention time of a naproxen glucuronide standard (not shown). The ability of each peak to promote binding of antibodies from patients 1 through 3 to platelets is shown (+/−). Positive results were obtained only with the peak corresponding to naproxen glucuronide.