Simultaneous determination of piroxicam and its major metabolite 5'-hydroxypiroxicam in human plasma by derivative spectrophotometry.

A first-derivative spectrophotometric method for the simultaneous determination of piroxicam (PX) and its major metabolite 5'-hydroxypiroxicam (OH PX) in human plasma is described. The method consists of direct extraction of the two drugs from the plasma samples with hydrochloric and trichloroacetic acid prior to their determination by measuring the first-derivative signals at 337.0 nm for PX and at 327.0 nm for OHPX (zero-crossing wavelength). The calibration graphs were linear up to 10.0 and 8.0 mg l-1 of PX and OH PX, respectively, and the limits of quantification were 0.27 and 0.56 mg l-1. The possible interfering effects of other substances were studied.