Enzyme immunoassay for mabuterol, a selective beta 2-adrenergic stimulant in the trachea

A sensitive double antibody and heterologous enzyme immunoassay for mabuterol was established. For competitive reactions, antibody raised against diazotized mabuterol-human serum albumin was incubated with a mixture of diazotized mabuterol analog (RC-1) labeled with beta-D-galactosidase and standard or sample. Free and antibody-bound enzyme hapten were separated using anti-rabbit IgG immobilized on polystyrene balls. Activity of the enzyme on the solid phase was fluorometrically determined. The present immunoassay allows detection of 0.5 to 100 pg/tube of mabuterol. Pharmacokinetic behavior of this agent in human plasma and urine was studied after a single oral administration (50 micrograms). The maximum level was achieved after 2-3 hrs with approximately 280 pg mabuterol /ml of plasma and the half life of mabuterol was estimated to be 19.5 hrs. Cumulative amount of mabuterol in the first 72 hrs urine was 64.3 +/- 13.2% of the administered dose.