text: Radioreceptor assays of ipratropium bromide in plasma and urine.
  Ipratropium bromide (Ipbr) is a frequently used quaternary anticholinergic administered by inhalation in the treatment of chronic obstructive lung diseases. Hardly any pharmacokinetic data are available, which can be useful in the optimisation of anticholinergic therapies. Hence, a radioreceptor assay (RRA) for Ipbr has been developed. The RRA is based on the competition between (3)H-N-methylscopolamine chloride ((3)H-NMS) and Ipbr for binding to lyophilised muscarinic receptors from calf brains. The assay has been optimised in respect of incubation conditions and extraction by ion-pair formation with sodium picrate. Detection limits of the drug were 5 ng ml(-1) in urine and 500 pg ml(-1) in plasma, after extraction of 2-ml samples. The method is applicable to monitoring the drug in plasma and urine after therapeutic dosing.