Radioreceptor assay for determination of the antimuscarinic drug ipratropium bromide in man.

A radioreceptor assay for the determination of ipratropium bromide in human plasma has been developed, using [3H] N-methyl-scopolamine as a radioligand to label muscarinic cholinergic receptors in a membrane preparation of rat cerebral cortex. There was no interference due to the cross-reactivity of 3 metabolites of ipratropium with the parent compound (5.2, 1.5 and 0.004%, respectively). The validity of the assay was checked between 20 pg/ml and 1000 pg/ml drug. In a pilot study plasma levels following a single oral dose of 30 mg were determined to examine the applicability of the radioreceptor assay to clinical and pharmacokinetic studies, and for measurement of plasma levels after therapeutic oral doses. The peak plasma concentration in three healthy volunteers (means = 322 pg/ml) occurred within 1-3 h.