Table 1 Criteria for patient selection

Patients with chronic cancer pain who had successfully completed the previous equivalence study. Notably, patients were required to have been in dose-stable pain control in the last 2 days of the CR phase of the study

Pure or predominantly neuropathic pain or pain of unknown origin (where a mechanism or physical cause could not be identified)

Patients requiring at least 8 mg of hydromorphone every 24 hours for the management of chronic cancer pain

A recent (within the previous 6 months) or current history of drug and/or alcohol abuse

Written informed consent

Women of childbearing potential who were pregnant or lactating, seeking pregnancy, or failing to take adequate contraceptive precautions (i.e. abstinence, an oral contraceptive, a hormonal implant, an intrauterine device, or condoms/diaphragm and spermicide)

Intolerance of or hypersensitivity to hydromorphone or other opioids

Dysphagia

Vomiting judged by the investigator sufficient to interfere with oral analgesia

Any gastrointestinal disorder (except gastrointestinal cancers), including pre-existing severe gastrointestinal narrowing (pathologic or iatrogenic) that may have affected the absorption or transit of orally administered drugs, particularly the insoluble OROS^® outer coating

Acute abdominal conditions that may have been obscured by opioids

Any significant central nervous system disorder including, but not limited to head injury, increased intracranial pressure, stroke within the previous 6 months, major clinical depression, and disorders of cognition which, in the opinion of the investigator, would interfere with the completion of patient assessments and study compliance (patients with stable cerebral metastases could be included)

Risk of serious decreases in blood pressure upon administration of an opioid analgesic (e.g. depleted blood volume, comprised vasomotor tone, circulatory shock)

Severe respiratory compromise or severely depressed ventilatory function, impaired renal or hepatic function, Addison's disease, hypothyroidism, prostatic hypertrophy, or urethral stricture which in the opinion of the investigator precluded the use of strong opioids

Receiving or received mono-amine oxidase inhibitors within the previous 2 weeks

Those previously entered into the study

Participation in another study with an investigational drug in the previous 4 weeks, or an analgesia study within the previous 8 weeks (with the exception of the equivalence study)