Influence of simulated weightlessness on the oral pharmacokinetics of acetaminophen as a gastric emptying probe in man: A plasma and a saliva study

This study evaluated the effect of simulated weightlessness on gastric emptying, using acetaminophen as a probe and 6degrees head-down bed rest to simulate zero gravity. Eighteen volunteers were given 1 g of acetaminophen orally before the bed rest and at days 1, 18, and 80. C-max, t(max), AUC(0-infinity), AUC(0-t), and t(1/2) were calculated for plasma and saliva. The plasma C.. showed a significant increase (10.43 mug/mL [day 1] to 14.74 mug/mL [day 80]), while t(max) significantly decreased (1.41 h [day 1] to 0.91 h [day 80]). Similar results were obtained with saliva, and there were significant increases in the AUCs. The good correlation between the plasma and saliva data suggests that saliva sampling can be valid for acetaminophen pharmacokinetics. The changes in C-max and t(max) indicated more rapid drug absorption, which could have been as a result of faster gastric emptying or an increased blood flow to the intestine.