The pharmacokinetics of morphine and lidocaine in nine severe trauma patients

Study Objective: To study the pharmacokinetic parameters of morphine and li docaine after a single intravenous (IV) bolus in severe trauma patients. Design: Clinical case study. Setting: Department of Anesthesiology and Intensive Care of a university ho spital. Patients: Nine patients, ages 24 to 91 years (mean 54.4 yrs), admitted to t he hospital with severe trauma (Injury Severity Score > 20) were included i n the study. Interventions: After initial evaluation and stabilization, a single IV 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. Measurements and Main Results: Morphine pharmacokinetics was studied in eig ht patients, lidocaine pharmacokinetics in seven patients, and both drugs w ere 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 volun teers (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). Conclusion: Changes is pharmacokinetics of drugs eliminated by the liver ma y occur in patients with severe trauma. The preserved lidocaine clearance i ndicates an almost normal hepatic blood flow and suggests that other mechan isms 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. (C) 2000 by Elsevier Science Inc.