Disposition of salmeterol xinafoate in laboratory animals and humans

The disposition of [14C]salmeterol xinafoate, a new inhaled beta 2-adrenoceptor agonist with both bronchodilator and antiinflammatory activity, has been studied in laboratory animals and humans following intravenous and oral administration. [14C]Salmeterol was rapidly absorbed in animal species and humans with Cmax observed within 2 hr. Cmax was similar for normalized oral dose level in mice, rats, and rabbits. In dogs, Cmax was higher and reflected the greater oral bioavailability in this species. The plasma t1/2, after intravenous administration, was 5 hr in rats and 2 hr in dogs. The volume of distribution of salmeterol was significantly greater than total body water in both rats (40 liters/kg) and dogs (6 liters/kg) and indicated high tissue uptake of the compound. Plasma clearance was high in rats (95 ml/min/kg) and dogs (30 ml/min/kg). Radioactive drug-related material was widely distributed throughout body tissues in rats. The highest concentrations were present in kidney, liver, gastrointestinal tract, pituitary, lung, heart, and bone marrow. Transfer of radioactive drug-related material across the placental barrier or into milk, studied in rats, was low. In all species the majority of an oral or intravenous dose (55-75%) was excreted in feces. Biliary excretion in rats and dogs accounted for 53% (0-27 hr) and 40% (0-8 hr) of an oral dose, respectively, indicating good absorption across the gastrointestinal tract. Enterohepatic circulation was significant in rats. Salmeterol was cleared predominantly by metabolism in animals and humans.(ABSTRACT TRUNCATED AT 250 WORDS)