MNTX 302
MNTX 302 showed that a gut-only opioid blocker injected under the skin produced a bowel movement within four hours in about half of people with advanced illness on strong painkillers, against about one in seven on placebo, without weakening pain relief; it was one of the two trials behind the US approval of Relistor.
Overview
MNTX 302 was a randomised, double-blind, placebo-controlled phase 3 trial of subcutaneous methylnaltrexone in adults with advanced illness and opioid-induced constipation who had not responded to stable laxatives. Patients received methylnaltrexone 0.15 mg per kilogram or placebo every other day for two weeks. The coprimary endpoints were laxation within four hours of the first dose and laxation within four hours after two or more of the first four doses.
In the NEJM 2008 report, 48 percent of patients on methylnaltrexone had laxation within four hours of the first dose versus 15 percent on placebo, and 52 percent versus 8 percent had laxation without a rescue laxative within four hours after two or more of the first four doses (P less than 0.001 for both). Median time to laxation was significantly shorter on methylnaltrexone. Abdominal pain and flatulence were the most common adverse events, and the paper reported no evidence of central opioid withdrawal or change in pain scores.
The US Relistor label names the same study Study 5 and analyses the same 133 patients (62 Relistor, 71 placebo); across its two advanced-illness studies most patients had a primary diagnosis of incurable cancer. The registry lists organisation id MNTX 302 as a completed phase 3 with an actual enrolment of 134. The programme treats opioid-induced constipation in advanced illness rather than a named cancer, so the record carries no cancer ids.
- 48 vs 15 out of 100 reached this endpoint with Methylnaltrexone 0.15 mg/kg compared with Placebo; 33 more per 100.
- Roughly one extra person helped for every 3 treated. That is a rough figure taken from the two percentages, not a guarantee for any one person.
- 52 vs 8 out of 100 reached this endpoint with Methylnaltrexone 0.15 mg/kg compared with Placebo; 44 more per 100.
- Roughly one extra person helped for every 2 treated. That is a rough figure taken from the two percentages, not a guarantee for any one person.
- The p-value (<0.001) says a difference this large would rarely happen by chance; it does not say how large or how useful the difference is.
- This endpoint is not one of the standard survival or response measures; read it alongside the trial's primary result.
- These results apply to the people the trial enrolled: Advanced illness with opioid-induced constipation despite stable opioids and laxatives: subcutaneous methylnaltrexone 0.15 mg per kilogram every other day for two weeks versus placebo. People in a different situation may not see the same effect.
Numbers are from the trial as recorded here; see the source links in the table below. This is orientation, not medical advice: ask your team how closely the trial population matches you.
133 randomised.
| Endpoint | Arm | n | Value | HR (95% CI) | p | Source |
|---|---|---|---|---|---|---|
| Laxation within 4 hours of the first doseprimary | Methylnaltrexone 0.15 mg/kg | - | 48% | - | <0.001 | link |
| Placebo | - | 15% | ||||
| Laxation without rescue laxative within 4 hours after two or more of the first four dosesprimary | Methylnaltrexone 0.15 mg/kg | - | 52% | - | <0.001 | link |
| Placebo | - | 8% |