Pharmacokinetic aspects of theophylline in premature newborns

To characterize further the pharmacokinetics of theophylline in premature infants, its concentration in blood was measured by high-pressure liquid chromatography after intravenous infusion given to six apneic premature newborns three to 15 days of age. Theophylline's apparent volume of distribution was 0.690±0.095 liters per kilogram (mean±S.E.), a value similar to that of children, but the half-life (30.2±6.5 hours) was nine times longer. Blood clearance rate(17.6±2.3 ml per kilogram per hour) was lower than plasma clearance rate (100 ml per kilogram per hour) of young children. At a total plasma concentration of 17 mg per liter, 56.4±3.8 and 36.4±3.8 per cent of the theophylline was bound to adult or full-term cord plasma proteins, respectively. Bilirubin and theophylline did not compete for plasma protein.