The first cardiovascular drug found to exhibit any difference in plasma levels between women and men was propranolol.
Women have higher serum concentrations of the parent drug.
It is assumed that there is no difference in this level of enzyme between men and women, despite some data stating that there is less activity in women. However, since there are many allelic variations, there may be increased, decreased, or no change in the activity of the isoenzyme CYP2D6. Another step in the metabolism of propranolol is the side-chain oxidation that is accomplished by two isoenzymes, CYP1A and CYP2C19. Their activity is less in women than in men. Propranolol also undergoes glucuronidation, a Phase II reaction.