Kinetics of intravenous theophylline

The pharmacokinetics of theophylline was studied in 6 normal, nonsmoking, adult male volunteers. A constant-rate intravenous infusion of 3.84 to 4.98 mg/kg of theophylline (as the ethylenediamine salt, aminophylline) was administered over 40 min. Serum theophylline concentrations were measured for 24 hr by means of a gas chromatographic method specific for theophylline. Within 30 min of an average intravenous dose of 4.4 mg/kg of theophylline, serum levels reached 10 microgram/ml. The highest serum level at the end of the infusion was 17 microgram/ml. The serum concentration-time data were fitted to a two-compartment open model and yielded a mean serum half-life (t1/2) of 11.02 hr, a value longer than those previously reported. Our results indicated that after the original loading dose of 4.4 mg/kg was infused for 40min, an immediate infusion rate of 1.40 mg/kg/hr (1.65 mg/kg/hr aminophylline) would be necessary to maintain a serum level of 10 microgram/ml.