If the hepatic extraction ratio Eh is approximately 0.8 and hepatic blood flow Qh is 90 L/h, estimate CLh and classify extraction.

• A. CLh ≈ 72 L/h; high extraction
• B. CLh ≈ 9 L/h; low extraction
• C. CLh ≈ 0 L/h; negligible extraction
• D. CLh ≈ 108 L/h; extreme extraction

Answer: (A)

The key idea is that hepatic clearance for a drug is the product of hepatic blood flow and the fraction of drug removed in a single pass, the extraction ratio. For a drug with a high extraction ratio, clearance is well described by CLh ≈ Qh × Eh.

Plugging in the numbers: Qh = 90 L/h and Eh = 0.8 gives CLh ≈ 90 × 0.8 = 72 L/h. Since Eh is 0.8, this is considered high extraction—the liver removes a large portion of the drug per pass, and the clearance is substantial but still limited by the hepatic blood flow (it’s less than 90 L/h, as expected).

Why the other numeric options don’t fit: a CLh of about 9 L/h would imply Eh ≈ 0.1, which is low extraction; a CLh near 0 would imply negligible extraction (Eh ≈ 0); a CLh of about 108 L/h would require an Eh > 1, which isn’t possible since extraction cannot exceed 1.