Study objective: To evaluate the safety of double-dose transdermal scopolamine patch therapy.
Design: Randomized, crossover, double-blind study.
Setting: Motion sickness clinic in Haifa, Israel.
Participants: Twenty male sailors aged 18-21 years whose seasickness symptoms improved only slightly or not at all with a single transdermal scopolamine patch.
Intervention: Subjects received either two transdermal scopolamine patches or one scopolamine patch plus a placebo patch for 24 hours (first session). After at least 1 week from the end of the first session, they received the other treatment for 24 hours (second session).
Measurements and main results: Plasma scopolamine concentrations, physiologic (heart rate and blood pressure), visual, and cognitive function parameters, and adverse effects were assessed before the first session (baseline) and after each 24-hour session. Visual function was tested again 24 hours after patch removal. Subjects also completed an adverse-effects questionnaire immediately after and 24 hours after patch removal for both treatment sessions. A significant difference was found in mean plasma scopolamine concentrations between the single-dose and double-dose treatments (81 vs 127 pg/ml [therapeutic level 100 pg/ml], p<0.01). No significant differences were found in heart rate, blood pressure, cognitive function, or visual function measurements. Mild blurred vision was the only adverse effect for which there was a significant difference between the single-dose and double-dose treatments; however, this adverse effect was judged to be not clinically significant.
Conclusion: Double-dose transdermal scopolamine may improve treatment in patients who fail to respond to a single patch by increasing the plasma scopolamine concentration, without aggravating systemic, visual, or cognitive adverse effects. Thus we recommend that a double dose can be administered safely to these patients.