Pharmacokinetics of intravenous terbutaline in asthmatic children

Seven asthmatic children were given terbutaline intravenously. The intact drug was measured in plasma and urine, and its conjugates were measured in urine. The decreasing plasma concentrations of terbutaline did not attain a terminal slope until 8-12 h after dosing. This was most likely due to different kinetics of the enantiomers. The terminal half-life was 8.8-15.8 h. Body clearance was 2.73-5.44 ml/min/kg, two-thirds of which were of renal origin. The volume of distribution (Vss) was 1.28-1.83 l/kg. The disposition pharmacokinetics of terbutaline do not rationalize a higher dose per kg body weight in children than in adults.