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The National Aeronautics and Space Administration (NASA) recommends using promethazine to prevent and treat space motion sickness, but pharmacologic responses in space and on Earth are different. Twelve volunteers were [...]

This study evaluated the effect of simulated weightlessness on gastric emptying, using acetaminophen as a probe and -6°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. Cmax, tmax, AUC0-∞, AUC0-t, and t1/2were calculated for plasma and saliva. The plasma Cmaxshowed a significant increase (10.43μg/mL [day 1] to 14.74μg/mL [day 80]), while tmaxsignificantly 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 Cmaxand tmaxindicated more rapid drug absorption, which could have been as a result of faster gastric emptying or an increased blood flow to the intestine. [ABSTRACT FROM PUBLISHER]