Sex Differences in Drug Metabolism

Abstract

AbstractSex differences in drug metabolism are recognized as a major determinant of sex differences in pharmacokinetics and an important contributor to interindividual differences in drug metabolism and, in some cases, drug action. Sex differences in human drug metabolism have also been observed with a variety of drugs. The biochemical basis of sex differences in hepatic drug metabolism was largely unknown until the 1980s when it was discovered that the expression of many drug‐metabolizing enzymes, including several members of the cytochrome P450 (CYP) superfamily, is sex dependent in rat and mouse liver. Well‐studied examples include rat enzymes CYP2C11, which is male specific in its expression, and CYP2C12 (female specific) and CYP2A1 (female predominant). The major gonadal hormones, testosterone and estradiol, regulate the sex‐dependent expression of rat hepatic CYP enzymes indirectly, through their effects on the hypothalamus and its regulation of the sexually dimorphic, ultradian rhythm of pituitary growth hormone (GH) secretion, which ultimately dictates the sex‐dependent patterns of expression of these CYPs and certain other drug‐metabolizing enzymes. In male rats, the intermittent, pulsatile pattern of GH secretion stimulates the expression of male‐specific liver enzymes, whereas the more continuous pattern of GH release in females suppresses the expression male‐specific enzymes while inducing female‐specific enzymes. The current view is that the transcription factors STAT5b and HNF4α coordinately regulate the action of GH and its resultant effect on the sex‐dependent expression of hepatic CYP genes and thus provide a molecular basis for sex differences in drug metabolism.