DEVELOPMENT OF A SENSITIVE RADIORECEPTOR ASSAY FOR OXYPHENONIUM IN PLASMA AND URINE

A radioreceptor assay (RRA) for oxyphenonium was developed. It is based on competition between [3H]dexetimide and oxyphenonium for binding to muscarinic receptors from calf striata. The RRA is optimized towards incubation medium and to extraction by ion pair formation with sodium picrate. At least 4 .times. 10-10 M of oxyphenonium is necessary to permit a reliable assay. This corresponds to a detection limit of drug of 2 ng/ml urine. After extraction, drug at 100 pg/ml of plasma can be estimated using 4 ml samples. The method is applicable to monitoring the drug and to the determination of its pharmacokinetics after therapeutic dosing. Urine levels can also be monitored.