Clinical study to investigate the efficacy, safety and tolerability of Naloxone in patients with opioid induced constipation.

Primary objectives: The primary objective of the trial is to demonstrate that administration of Naloxone HCl PR (prolonged-release) tablets once daily is superior to Naloxone HCl PR Placebo in the improvement / reversal of opioid-induced constipation (OIC) as determined by the Bowel Function Index (BFI). Primary end point is defined as the absolute change in BFI score at the end of Week 12 (Visit 11) compared to baseline (Visit 4).