Ground-based investigations to establish the S/P ratios of scopolamine have been conducted in normal subjects. Following intravenous and oral administration, scopolamine readily distributes into saliva with consistent S/P ratios over the entire disposition profile. In this investigation, the pharmacokinetics of scopolamine/dextroamphetamine following oral administration to crewmembers before and during space flight were evaluated using salivary concentrations to estimate the disposition parameter changes of anti-motion sickness agents during missions.
Evaluation of the salivary concentration-time profiles indicated that large deviations in the concentration-time profiles of scopolamine in crewmembers occur during space flight when compared to their ground-based control profiles. In one crewmember, a significant decrease in the peak concentration and an increase in the time to reach peak concentration were observed, while opposite results were obtained for another crewmember.
The third crewmember repeated the study twice during the mission, and the changes in both instances were relatively small when compared to the results from the other crewmembers. Large intersubject variability, inadequate sample volumes, and insufficient data make it very difficult to reliably assess the pharmacokinetic behavior of scopolamine in crewmembers during space flight. The use of scopolamine was subsequently discontinued due to its unreliable effectiveness and a reported rebound effect after discontinuing it.
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