Cytochrome P450, family 2, subfamily C polypeptides 9 and 19 are part of the CYP2C subfamily and are responsible for metabolizing many important drugs. CYP2C19 accounts for about 20% of the cytochrome p450 in adult liver. CYP2C9 contributes to the metabolism of fatty acids, prostanoids, and steroid hormones, and it may catalyze potentially toxic bioactivation reactions. A significant negative correlation (r = -0.572, P < .01) between enzyme activity and age was observed for CYP2C19, but there were no sex differences.