Figure 3-7 Relationships among liver blood flow (Q), clearance, and the extraction ratio. For drugs with a high extraction ratio, clearance is nearly identical to liver blood flow. For drugs with a low extraction ratio, changes in liver blood flow have almost no effect on clearance. (Adapted from Wilkinson GR, Shand DG: Comentary: A physiological approach to hepatic drug clearance. Clin Pharmacol Ther 18:377–390, 1975.)