Assessment of the Pharmacokinetic, Pharmacodynamic, Pharmacogenetic Relationships of Morphine and Metabolites After Severe Postoperative Pain in Adults

No previous study attempted to characterize the pharmacodynamic, pharmacokinetic, and pharmacogenetic relationships of morphine in the early postoperative period, whereas it is the main clinical situation for severe pain and a unique model for its study (not possible in the healthy volunteer). Indeed, intravenous titration of morphine is the first step for pain control in the postanesthesia care unit. Administration of intravenous boluses of morphine enables to obtain complete pain relief in 98% of the patients. We intend to study the effects of morphine (intravenous titration then patient-controlled intravenous administration (PCA) for 24 hours), perform dosages of plasma concentration of morphine an its main metabolites, and also study gene polymorphisms coding for main proteins involved in the pharmacokinetic and pharmacodynamic profile of morphine (hepatic metabolism, distribution and elimination, interaction with morphine receptor). Five hundred patients scheduled for major orthopedic surgery will be included in this prospective study. The main objective of this study is to improve our knowledge on the pharmacodynamic, pharmacokinetic, and pharmacogenetic relationships of morphine administered to relief severe postoperative pain. The analysis will encompass the efficacy (acute during titration and subacute during the first 24 hours) and adverse effects of morphine. Our purpose is also to better characterize the age- and sex-related differences which probably markedly differ between the two periods (acute vs subacute). We consider that this knowledge is important to confirm or not several important concepts currently used to define the appropriate analgesic regimen to control severe pain in the postoperative period.