A comparison of plasma levels of hyoscine after oral and transdermal administration

Hyoscine (Scopolamine) has a long history of use as an effective drug in the treatment of motion illness [l, 21. Its side effects are fairly well documented [3], and have generally been considered preferable to motion illness [4]. However, a reduction in the side effects of hyoscine while retaining its efficacy would be desirable. A system has been developed (Alza Corporation, Palo Alto, California) which allows hyoscine to be absorbed across the skin and is designed to produce low, sustained circulating hyoscine levels. This preparation, known as the transdermal therapeutic system, utilizes a small adhesive film attached behind the ear, where favourable skin permeation properties ensure that the rate of drug release determines the rate of entry into the circulation. The rate of release is controlled by a microporous membrane interposed between Ihe reservoir and the adhesive. This route of administration should ensure absorption of hyoscine even when the patient is vomiting. The time course of the concentration in the blood, however, is clearly important. Variations in absorption, distribution and metabolism make it impossible to predict blood concentrations from the amount of drug administered. Before any significant comparison can be made of the efficacy of the oral and transdermal routes for hyoscine, there is clearly a need for an adequately sensitive and reliable method for determining plasma levels of the drug. This is particularly important in view of a recent report [5] which showed that for a given oral dose of benztropine a wide variation of blood levels was produced. The only alternative. the use of some physiological response to provide a built-in assay, is unlikely to be sufficiently sensitive.