Which statement correctly defines a high extraction drug in hepatic clearance?

• A. CLh is much less than Qh
• B. CLh approximates Qh
• C. CLh is independent of Qh
• D. CLh is approximately fu*CLint

Answer: (B)

High extraction drugs are cleared by the liver at a rate limited by liver blood flow rather than by the enzyme’s capacity. In the well-stirred model, hepatic clearance is CLh = Qh × (fu×CLint) / (Qh + fu×CLint). When fu×CLint is much larger than Qh, the fraction becomes close to 1, so CLh ≈ Qh. That means the clearance essentially matches the liver’s blood flow, which is the hallmark of a high extraction drug. The other scenarios correspond to low extraction, where CLh would be governed by fu×CLint (not by Qh), and thus CLh would be much less than Qh and not approximate it.