Absorption and metabolism of acetaminophen shortly before parturition.

The absorption and metabolism of acetaminophen 1 g po (as tablets) by a healthy 27-year-old woman was determined one day before parturition and again 38 days after parturition. Based on the urinary excretion data, acetaminophen was absorbed much more slowly and incompletely, and the metabolic conversion of acetaminophen to the sulfate conjugate was less pronounced on the last day of pregnancy than 38 days after parturition. These results are consistent with reports of decreased gastric emptying rate in late human pregnancy and with decreased acetaminophen sulfation by rats during the last days of gestation.