An Efficacy and Safety Study to Compare Morphine 6-glucuronide (M6G) and Morphine in Patients Suffering With Post-Operative Pain for at Least 24 Hours

Inclusion Criteria: * Male or female patients undergoing any of the following elective surgical procedures that, in the Investigator's opinion, would have required the use of post-operative patient controlled analgesia for a minimum of 24 hours: * Abdominal hysterectomy with the exception of laparoscopic procedures. * Bowel / gastrointestinal (GI) surgery * Major urological surgery * Aged ≥ 18 years * American Society of Anesthesiologists (ASA) grades I to III * If female, the patient had to be post-menopausal (last menstruation \> 1 year previously), or surgically sterile (e.g. full hysterectomy or tubal ligation). If neither of these was the case, she had to use adequate contraception (i.e. hormonal contraceptive, intrauterine device (IUD), or a double barrier method) and to have a negative urine pregnancy test during the 24-hours prior to surgery. * Provide written informed consent to participate in the trial prior to surgery. Exclusion Criteria: * The patient was pregnant or lactating. * Had a known sensitivity to morphine or other opiates, or a medical condition such that opiates were contraindicated. * Had a known sensitivity to paracetamol, or a medical condition such that paracetamol was contraindicated. * Had received any investigational drug within the 90 days prior to the start of the study, or was scheduled to receive one during the study period. * Had been involved in any previous M6G study. * Had a documented history or current evidence of alcohol or drug abuse within the year prior to screening. * Had clinically significant findings on pre-treatment evaluations (e.g. laboratory results, electrocardiograms, medical history, physical examination) that, in the Investigator's opinion, should have excluded them from the study. * Had a concurrent disorder that resulted in excessive pain that, in the Investigator's opinion, would have interfered with the pain assessments during the study (e.g.severe rheumatoid arthritis, muscle dystrophy or neuropathic pain). * Had a blood clotting disorder or other blood dyscrasias. * Had requested the use of epidural or intrathecal anaesthesia techniques. * Required the use of a local anaesthetic block and/or infiltration of wound sites. * Required the concomitant use of opioids or non-steroidal anti-inflammatory drugs(NSAIDs) during the study due to an existing concurrent condition. * Had a history of Left Ventricular Failure or compromised cardiovascular function, defined as New York Heart Association (NYHA) level 3. * Had a history of severe renal impairment or a creatinine level \> 3 times the upper limit of normal. * Was having surgery that would have prevented the use of oral or rectal paracetamol(iv administration of paracetamol was not allowed). * Was expected to require prolonged ventilation after surgery. * Was opioid tolerant or had a history of chronic opioid use. * Had cognitive impairment that would, in the Investigator's opinion, have precluded participation or compliance with protocol defined procedures (i.e. use of PCA).