Figure 3-3 Clearance represents the flow of blood or plasma that is completely cleared of drug. If all of the drug is extracted by the clearing organ (i.e., extraction ratio ≅ 1), clearance is the flow to the organ, as illustrated here. (Adapted from Shafer S: Principles of pharmacokinetics and pharmacodynamics. In Longnecker DE, Tinker JH, Morgan GE [eds]: Principles and Practice of Anesthesiology, 2nd ed. St. Louis, Mosby-Year Book, 1997.)