A Study Comparing Oxycodone to Oxycodone/Naloxone in Moderate to Severe, Chronic Cancer Pain

Inclusion Criteria: 1. Male or female subjects at least 18 years or older with a diagnosis of cancer. 2. Females less than one year post-menopausal must have a negative urine pregnancy test recorded at the screening visit, be non-lactating, and willing to use adequate and highly effective method of contraception throughout the study. Highly effective methods of birth control are defined as those which result in a low failure rate (i.e. less than 1% per year) when used consistently and correctly such as sterilization, implants, injectables, combined oral contraceptives, some IUDs (hormonal), sexual abstinence or vasectomised partner. 3. Subjects who are receiving WHO step II or Step III analgesic medication who have constipation induced, or worsened by their opioid medication, as shown by 1. the subject's medical need of regular intake of laxatives to have at least 3 bowel evacuations per week, or having less than 3 bowel evacuations when not taking a laxative, respectively. 2. the subject's self-assessment that their constipation was induced or worsened by their current pre-study opioid medication. 4. Documented history of moderate to severe, chronic cancer pain that requires around-the-clock opioid therapy (starting dose at the beginning of the double-blind phase of oxycodone PR between 20 - 80 mg/day) and are likely to benefit from WHO step III opioid therapy for the duration of the study. Subjects must be willing to discontinue their current opioid analgesic routine. 5. Subjects are willing to discontinue pre-study laxative medication and take study specific laxative medication. 6. Subjects taking daily fibre supplementation or bulking agents are eligible if they can be maintained on a stable dose and regimen throughout the study, and in the investigators opinion are willing and able to maintain adequate hydration. 7. Subjects willing and able (e.g. mental and physical condition) to participate in all aspects of the study, including use of medication, completion of subjective evaluations, attending scheduled clinic visits, completing telephone contacts, and compliance with protocol requirements as evidenced by providing written, informed consent. 8. Subjects already taking non-opioid analgesics and all other concomitant medications (including those for the treatment of depression) are eligible to take part in the study. However, all concomitant medications that are considered necessary for the subject's welfare should be continued at a stable dose throu…