MORPHINE PHARMACOKINETICS IN PREMATURE AND MATURE NEWBORN-INFANTS

The pharmacokinetics of a single dose of morphine was investigated in live term infants (gestational age 37-40 weeks) and eight preterm infa nts (gestational age 25-32 weeks). In the five term infants, median (r ange) volume of distribution at steady state (Vd(beta)) was 1758 (634- 2700) ml/kg, plasma clearance (Cl) was 4.73 (1.75-6.61) ml/kg/min and terminal half-life (T1/2) was 224 (107-394) min. In the eight preterm infants, Vd(beta) was 2366 (1662-2876) ml/kg, Cl was 2.82 (1.88-6.60) ml/kg/min and T1/2 was 556 (248-834) min. No correlation was found bet ween clearance and gestational age, but we found a significant negativ e correlation between T1/2 and gestational age. We conclude that there is considerable variation in the pharmacokinetic properties of morphi ne in both term and preterm newborn infants. Because of this variation , careful individual assessment of the clinical effect of therapy with morphine in newborn infants should be exercised.