Morphine kinetics in children.

The kinetics of morphine in the plasma of children (0 to 15 yr) can in most cases be adequately described by a triexponential function. When the dosage in children receiving morphine as premedication before surgery is based on kilograms of body weight, there are only minor differences in the kinetic patterns of morphine at different ages (0 to 1, 1 to 7, and 7 to 15 yr). No significant difference in the morphine kinetics was observed between patients (7 to 15 yr) receiving the drug only as premedication and those who also received doses during surgery. The minimum morphine concentration in plasma necessary to suppress the clinical signs of pain during surgery was found to be 65 ng/ml (95% confidence limits of 46 to 83 ng/ml). Based on these minimum effective plasma levels of morphine, there does not seem to be any difference between children of different ages in their sensitivity to morphine. No difference was found in the minimum effective level of morphine when clinical signs of pain were observed by different anesthesiologists.