Fluorometric determination of chlorzoxazone in tablets and biological fluids.

A fluorometric determination for chlorzoxazone was developed based on the intrinsic drug fluorescence in chloroform using excitation and emission wavelengths of 286 and 310 nm, respectively. A calibration curve for chlorzoxazone in chloroform gave a linear working range of 0.027-2.3 microgram/ml (r = 0.9999) with the minimum detectability at 27 ng/ml. The procedure was applied to chlorzoxazone analysis in spiked plasma and urine samples. Minimum detectable drug levels in these samples were 60 and 130 ng/ml, respectively. Data revealed that chlorzoxazone could be determined in plasma and urine even in the presence of 20-fold molar excesses of its major metabolite, 6-hydroxychlorzoxaxone, and acetaminophen. The method also was applicable to chlorzoxazone analysis in a commercial dosage form containing acetaminophen.