The Pharmacy and Therapeutics Committee at the authors’ institution reviewed the protocol for this study, and approval was obtained from the Research Ethics Board. The study began in July 2001, and the original goal was to recruit 50 patients. However, in July 2002 the study was interrupted by a labour disruption and was never resumed.

INTRODUCTION Morphine is commonly used as an analgesic for the control of postoperative pain and is the “gold stan­dard” against which all other analgesics are compared. Morphine acts mainly as an agonist at specific receptor sites in the central nervous system. Evidence suggests that both hyperanalgesic effects after tissue injury and opioid tolerance involve activation [...]