The pharmacokinetics of morphine and lidocaine in nine severe trauma patients

To study the pharmacokinetic parameters of morphine and lidocaine after a single intravenous (i.v.) bolus in severe trauma patients.

Clinical case study.

Department of Anesthesiology and Intensive Care of a university hospital.

Nine patients, ages 24 to 91 years (mean 54.4 yrs), admitted to the hospital with severe trauma (Injury Severity Score > 20) were included in the study.

After initial evaluation and stabilization, a single i.v. dose of morphine 0.025 mg/kg and lidocaine 1.5 mg/kg was given separately, and blood samples were drawn for each drug serum concentration.

Morphine pharmacokinetics was studied in eight patients, lidocaine pharmacokinetics in seven patients, and both drugs were studied in six patients. Morphine clearance 2.5 to 10 ml/kg/min (6 +/- 2.6, mean +/- SD) and volume of distribution 0.28 to 3.30 L/kg (1.4 +/- 1.0) were found to be lower than values described previously for healthy volunteers (33.5 +/- 9 ml/kg/min and 5.16 +/- 1.40 L/kg, respectively), and are similar to those described in trauma patients (5 +/- 2.9 ml/kg/min and 0.9 +/- 0.2 L/kg, respectively). In contrast, lidocaine clearance 4.5 to 9.4 ml/kg/min (6.7 +/- 1.7) and volume of distribution 0.39 to 1.20 L/kg (0.72 +/- 0.28) were similar to the value described in healthy volunteers (10 ml/kg/min and 1.32 L/kg, respectively).

Changes in pharmacokinetics of drugs eliminated by the liver may occur in patients with severe trauma. The preserved lidocaine clearance indicates an almost normal hepatic blood flow and suggests that other mechanisms may be involved in the lower morphine clearance. The findings may have applications for the treatment of severe trauma patients and suggest that drug monitoring might be needed in some instances so as to avoid toxicity.