Pharmacokinetics of chlorzoxazone in humans.

Twenty-three normal male subjects received 900 mg of acetaminophen and 750 mg of chlorzoxazone as an oral suspension. Analysis of plasma samples indicated a rapid absorption and rapid elimination of chlorzoxazone. Average values of the elimination half-life and plasma clearance were 1.12 +/- 0.48 hr and 148.0 +/- 39.9 ml/min, respectively. Analysis of urine samples showed that chlorzoxazone was eliminated from the body as the glucuronide conjugate of the intermediate metabolite 6-hydroxychlorzoxazone, to the extent of 74% of the dose. The plasma and the urinary excretion data were fitted to theoretical equations, and excellent fits were obtained using a five-parameter pharmacokinetic model.