Alcohol Pharmacokinetics
Ethanol is absorbed rapidly from the stomach (20%) and small intestine (80%) into the bloodstream, reaching peak blood alcohol concentration (BAC) 30-90 minutes after the last drink. Absorption is slowed by food in the stomach (particularly fatty foods), and accelerated by carbonation and higher alcohol concentrations. Elimination occurs primarily through hepatic oxidation by alcohol dehydrogenase (ADH) at a roughly constant rate—the average person eliminates approximately 0.015-0.020 g/dL per hour (Widmark's elimination rate). This means a person at 0.08% BAC (the legal driving limit in all U.S. states) would take approximately 4-5 hours to reach 0.00%. Retrograde extrapolation—calculating what the BAC was at the time of driving based on the BAC measured later—is commonly used in DUI prosecution but requires assumptions about absorption phase, elimination rate, and time of last drink.