A semi-automated solid-phase extraction and radioreceptor assay for the analysis of scopolamine in urine and plasma

In a double-blind placebo-controlled cross-over study, we evaluated the therapeutic efficacy of transdermal scopolamine in ten patients with reversible airways obstruction. They received a patch (Scopoderm^® TTS) behind the ear for three days and samples of blood and urine were taken. A highly sensitive method was developed and validated to measure the low levels of free and total scopolamine in urine and plasma. The procedure consisted of a semi-automated solid-phase extraction followed by the analysis using radioreceptor assays. The mean plasma concentrations, taken every third patch day, of free and total scopolamine were 43.6 pg/ml and 229.0 pg/ml, respectively. In 24-h urine, collected every second patch day, 6.3 μg of free scopolamine and 83.4 μg total scopolamine was excreted. This means that 70% of the delivered dose (120 μg in 24 h) is excreted in urine. For urine samples, the limit of detection (LOD) of the assay is 550 pg/ml and the limit of quantitation (LOQ) is 610 pg/ml. For plasma samples, the LOD is 16 pg/ml and the LOQ is 38 pg/ml.