Morphine pharmacokinetics during anesthesia and surgery in patients with burns

The plasma clearance, plasma half-life, and apparent volume of distribution of morphine during anesthesia and surgery were determined in seven patients with burns and compared with seven age-matched control subjects. The burn group had a significantly lower clearance, longer terminal half-life, and smaller volume of distribution than the control group. The clearance was 12 ± 2 ml/min/kg, the half-life was 123 ± 24 minutes, and the volume of distribution was 2.2 ± 0.4 L/kg for the subjects with burns compared with 25 ± 3 ml/min/kg, 89 ± 18 minutes, and 3.2 ± 0.8 L/kg for the control subjects (P < 0.001, <0.02, and <0.02, respectively). These data contrast with the theory that patients with burns have a tolerance to narcotics and suggest the need for further study of the pharmacologic effects of burn injury and surgery.