Pharmacokinetics of intravenous N-acetylcysteine in pre-term new-born infants

Background: Reactive oxygen species have been considered to play a role in several clinical complications in pre-term infants. The aim of this study was to determine the pharmacokinetics of intravenous N-acetylcysteine in pre-term neonates. This information is needed to evaluate the use of N-acetylcysteine as an antioxidant in this patient group. Methods: N-acetylcysteine was infused intravenously in ten patients (gestational age 24.9-31.0 weeks, weight 500-1384 g) for 24 h (3.4-4.6 mg/kg/h), starting 2.0-11.2 h from birth (study I) and in six patients (gestational age 25.9-29.7 weeks, weight 520-1335 g) for 6 days (0.3-1.3 mg/kg/h), starting at the age of 24 h (study II). Arterial plasma N-acetylcysteine and cyst(e)ine concentrations were determined from timed samples taken during (study I and II) and after (study I) the N-acetylcysteine infusion. Results: In study I, the mean elimination half-life of N-acetylcysteine was 11 h (range 7.8-15.2 h). The mean plasma clearance of N-acetylcysteine was 37 ml/kg/h (range 13-62 ml/kg/h) and the mean volume of distribution was 573 ml/kg (range 167-1010 ml/kg). The plasma clearance and volume of distribution correlated with weight (r = 0.81, P < 0.01, and r = 0.78, P < 0.01, respectively) and with gestational age (r = 0.71, P < 0.05, and r = 0.64, P < 0.05, respectively). In study II, the steady-state concentration of N-acetylcysteine was reached in 2-3 days in five of six patients during a constant infusion. Conclusions: The pharmacokinetics of N-acetylcysteine in pre-term infants depend markedly on weight and gestational age. The elimination of N-acetylcysteine is much slower in pre-term new-borns than in adults.