Abstractscavenges free radicals of oxygen (Feuerstein et al., 1997). It is used to treat systemic arterial hypertension (Cournot et al., 1992;Lund-Johansen et al., 1992) and congestive heart failure (DasGupta et al., 1991) and is purported to improve exercise capacity (Cleland et al., 1996;Hampton, 1996) and longevity in humans .Carvedilol is well absorbed from the gastrointestinal tract, but is subject to considerable fi rst-pass metabolism in the intestinal and/or liver (McTavish et al., 1993;Morgan, 1994). Carvedilol is more than 98% bound to plasma proteins. Carvedilol is metabolized by both oxidation and conjugation pathways in the liver into some metabolites (Neugebauer et al., 1987;Neugebauer and Neubert, 1991). The oxidation pathways are mainly catalyzed by CYP2C9 enzymes in human (McTavish et al., 1993;Morgan, 1994;Oldham and Clarke, 1997), and then CYP2D6 is responsible for the formation of 4'-hydroxy carvedilol and 5'-hydroxy carvedilol, and both metabolites are excreted into urine (Neugebauer and Neubert, 1991). Since carvedilol is a substrate of both CYP2C9 en-