DETERMINATION OF PIROXICAM AND ITS MAJOR METABOLITE 5-HYDROXYPIROXICAM IN HUMAN PLASMA BY ZERO-CROSSING FIRST-DERIVATIVE SPECTROPHOTOMETRY

A zero-crossing first-derivative spectrophotometric method for the det ermination of piroxicam and its major metabolite 5-hydroxypiroxicam (5 -HP) in human plasma is described. This technique permits the quantifi cation of compounds with closely overlapping spectral bands without an y separation step. The method consists of direct extraction of the les s-ionised forms of piroxicam and 5-hydroxypiroxiam with pure diethyl e ther. First derivative values at 343.5 and 332.5 nm for piroxicam and 5-HP, respectively, were obtained. The absolute recovery of the method was found to be 89.4% for piroxicam and 90.3% for 5-HP. Calibration g raphs are linear (r better than 0.9998), with zero-intercept, in the c oncentration range 0.5-12.0 mu g ml(-1) for both compounds. The limits of quantification attained according to the IUPAC definition were 0.2 9 and 0.27 mu g ml(-1) for piroxicam and 5-HP, respectively. The resul ts obtained by the proposed method were in good agreement with those f ound by the high-performance liquid chromatographic method (HPLC). (C) 1998 Elsevier Science B.V. All rights reserved.