This is a multicenter, randomized, double-blind , placebo-controlled trail to investigate the safety and efficacy of subcutaneous methylnaltrexone for treating opioid-induced constipation in patients with advanced illness.

Methylnaltrexone is a quaternary derivative of the pure opioid antagonists naltrexone. It is fairly lipid soluble and readily cross the blood-brain barrier. This property provides methylnaltrexone with the potential to block the undesired side-effects of opioid pain medications predominantly mediated by receptors located peripherally while sparing opioid effects mediated at receptors in the central nervous system, most importantly analgesia.

This is a multicenter, randomized, double-blind , placebo-controlled trail to investigate the safety and efficacy of subcutaneous methylnaltrexone for treating opioid-induced constipation in patients with advanced illness. The randomization schedule was used to assign patients in a 2:1 ratio to multicenter or an equal volume of placebo administered subcutaneously on alternate days for 2 weeks. The clinical trail was estimated to enroll 180 patients totally.

Inclusion Criteria:

• A life expectancy of 3 month or more
• Qualifying patients received opioids for analgesia for 1 week or more and a stable regimen of opioids and laxatives for 3 or more days before study entry
• Patients had opioid-induced constipation with either fewer than three laxation during the preceding week and no clinically meaningful laxation (as determined by the in investigator ) within 24h before the first study dose or no clinically meaningful laxation within 48h before the first study dose
• During the two-week trail , patients would keep their life habits (dietary fiber , fluid intake and physical activity)
• Patients volunteered for the trail
• Women of childbearing potential had negative pregnancy tests. Both male and female patients need to take effective contraceptives to avoid pregnancy.

Exclusion Criteria:

• Constipation that was not primarily caused by opioids ( as determined by the investigator)
• Mechanical gastrointestinal obstruction, an indwelling peritoneal catheter, clinically active diverticular disease , fecal impaction , acute surgical abdomen , and fecal ostomy
• Patients had the surgery plan which would effect the results of pain assessment
• Patients had hypersensitivity to methylnaltrexone , naltrexone or naloxone or if any investigational drug or experimental product