Extraction Ratio (E)

The fraction of drug removed from the blood during a single passage through an eliminating organ, calculated as (arterial concentration minus venous concentration) divided by arterial concentration. Drugs with high extraction ratios (>0.7) have flow-dependent clearance, while those with low extraction ratios (<0.3) have capacity-dependent clearance sensitive to enzyme activity and protein binding changes.

例

• Morphine: high hepatic extraction ratio (~0.7), significant first-pass effect
• Diazepam: low extraction ratio (~0.03), minimal first-pass metabolism
• Nitroglycerin: very high extraction ratio (~0.99), requires sublingual/transdermal routes to bypass first-pass