Kinetics and dynamics of postoperative intravenous morphine in children.

The pharmacokinetics of intravenous morphine were determined in three groups (0 to 1/2, 2 to 4, and 6 years) of children and related to the respiratory rate, arterial PCO2, and postoperative analgesia. With respect to pharmacokinetics, children seem to mature very early, because in patients aged 5 to 6 months corresponding parameters similar to those in adults were encountered. The two youngest patients (11 days and 2.4 months) diverged clearly from the others. Their mean plasma clearance of morphine was 5.2 ml/min/kg and volume of the central compartment was 0.36 L/kg. In the other patients the clearance ranged from 25.8 to 75.6 ml/min/kg and volume of central compartment from 0.67 to 2.07 L/kg, respectively. The mean analgetic concentration of morphine was 26.2 micrograms/L in the youngest group and 3.8 micrograms/L in the other patients. The effect of morphine on respiration was similar in all groups and did not differ from that of adults. The respiratory depressant effect of morphine in the two youngest patients was not analyzed.