Safety of double-dose transdermal scopolamine

To evaluate the safety of double-dose transdermal scopolamine patch therapy.

Randomized, crossover, double-blind study.

Motion sickness clinic in Haifa, Israel.

Twenty male sailors aged 18-21 years whose seasickness symptoms improved only slightly or not at all with a single transdermal scopolamine patch.

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).

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.

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.