A sensitive radioreceptor assay for atropine in plasma

The development of a sensitive, relatively simple radioreceptor assay for atropine in plasma is reported. It is based on the ability of anti-muscarinic compounds to compete with tritiated quinuclidinyl benzilate for muscarinic receptor binding sites. As little as 300fmol (3 × 10^?10M) atropine could be reliably assayed, the extraction procedure permitting the estimation of 3 pmol (0.9 ng) atropine per ml of plasma. The method has been applied to the determination of plasma concentration-time profiles after i.m. administration of atropine to man, and could probably be extended to other anti-muscarinic drugs.