A sensitive radioreceptor assay for determining scopolamine concentrations in plasma and urine

A sensitive and reliable procedure for the quantitation of low picogram levels of scopolamine in plasma and urine is described. The method consists of two steps, a preparative extraction step using C₁₈ columns (Sep‐Pak), followed by an analytical quantitation step involving a muscarinic radioreceptor assay. The extraction efficiency of the C₁₈ columns was 85–95% for both plasma and urine over a wide concentration range. When [³H]methyl scopolamine is used as a tracer, the assay can detect picogram concentrations (>25 pg) of scopolamine (base) in plasma and urine. The applicability of the procedure for therapeutic drug monitoring of scopolamine was demonstrated by using the method to determine plasma levels in humans after transdermal administration.