[Biochemical studies with oxitropium bromide. 2. Pharmacokinetics and metabolism in humans]

The present paper reports on the human pharmacokinetics of (8r)-6 beta, 7 beta-epoxy-8-ethyl-3 alpha-/(-)-tropoyloxy/-1 alpha H, 5 alpha H-tropanium bromide (oxitropium bromide, Ba 253 BR, Ventilat) after intravenous and oral administration as well as following inhalation. The 14C-labelled substance was used. The concentrations of radioactivity measured in the plasma after i.v. administration show a biphasic course, a rapid alpha phase and a terminal phase (t 1/2 = 1.5 h). Once the alpha phase has passed the radioactivity concentrations measured after i.v. administration of 1 mg are comparable with those after 20 mg administered orally. The concentration course after inhalation corresponds essentially to the course after oral administration of lower doses. The cumulative renal excretion of the radioactivity is 68-78% for i.v. administration, 13% for oral administration, and 10% for inhalation. 7% (i.v.), 77% (p.o.) and 88% (inhalation) is excreted in the faeces. Oxitropium bromide is rapidly hydrolysed after oral administration. As little as 4 h later only 2-3% of intact active ingredient is found, whereas there is 85% of the hydrolysed product in the urine. A similar distribution pattern is observed in urine samples taken later. Some other metabolites are also recorded in minimal quantities. After i.v. administration, too, the hydrolysed product is excreted as the main component.