Scopolamine patch to prevent seasickness: clinical response vs. plasma concentration in sailors

Scopolamine is highly effective for the treatment of seasickness. Nevertheless, transdermal therapeutic system (TTS) scopolamine, despite high compliance on the part of persons treated by the drug, fails to provide protection against seasickness in 26-38% of patients. To the best of our knowledge, the correlation between scopolamine levels in plasma and its therapeutic effect under sailing conditions in the open sea is investigated for the first time in the present study.

Subjects were 61 crewmembers of naval vessels treated by TTS scopolamine. The therapeutic response at sea was documented by questionnaire. During a period ashore, a TTS scopolamine patch was applied in the same subjects. Blood samples were taken and an adverse effects questionnaire completed 8 h after scopolamine patch application. Scopolamine levels were determined using an established radio-receptor assay procedure. To verify the reproducibility of these measurements, blood samples were taken twice from most subjects, on separate days after different patch applications. Subjects were divided into "responders," who reported at least a moderate decrease in seasickness severity compared with their previous experience at sea without TTS scopolamine therapy, and "non-responders," who had only slight symptomatic relief or no relief at all.

The mean scopolamine concentration in the plasma of the 37 responders (156.77 +/- 77.03 pg x ml(-1)) was significantly higher than the mean level in the 24 non-responders (97.03 +/- 73.34 pg x ml(-1); p = 0.005, simple t-test).

Attempts to increase scopolamine levels in plasma by increasing the drug dosage or improving transdermal absorption should be considered for the treatment of "non-responders".