Use of measurements of ethanol absorption from stomach and intestine to assess human ethanol metabolism.

Controversy exists concerning the site (stomach vs. liver) and magnitude of first-pass metabolism of ethanol. We quantitated gastric and total ethanol absorption rates in five male subjects and utilized these measurements to evaluate first-pass metabolism. Gastric emptying of ethanol (0.15 g/kg) was determined via a gamma camera and gastric absorption from the ratio of gastric ethanol to [14C]polyethylene glycol. Gastric absorption accounted for 30% and 10% of ethanol administered with food and water, respectively. With food, estimated gastric mucosal ethanol concentrations fell from 19 to 5 mM over 2 h. Calculations using these concentrations and kinetic data for gastric alcohol dehydrogenase showed <2% of the dose underwent gastric metabolism. Application of observed ethanol absorption rates to a model of human hepatic ethanol metabolism indicated that only 30% and 4% of the dose underwent first-pass metabolism when administered with food and water, respectively. We conclude that virtually all first-pass ethanol metabolism occurs in the liver and first-pass metabolism accounts for only a small fraction of total clearance.