Background and Objectives In patients with chronic noncancer pain, subcutaneous methylnaltrexone for opioid-induced constipation (OIC) was examined in a randomized controlled trial (RCT) followed by an open-label extension (OLE). This study examined the reproducibility of RCT findings by analyzing data from placebo-treated patients who crossed over to methylnaltrexone.

Methods Adults with less than 3 weekly rescue-free bowel movements (RFBMs), taking 50 mg or more of an oral morphine equivalent per day, were randomized to receive methylnaltrexone 12 mg or placebo for 4 weeks, followed by open-label methylnaltrexone 12 mg as needed for 8 weeks.

Results A total of 134 placebo-treated patients (median morphine equivalent dose, 150 mg/d; mean of 1.1 RFBM per week) crossed over to methylnaltrexone in OLE. During the RCT, 9.7% of placebo-treated patients experienced an RFBM within 4 hours of first dose and 9.0% of all placebo injections resulted in an RFBM within 4 hours compared with 45.9% and 34.5%, respectively, with methylnaltrexone treatment in the OLE. When expressed as percentage of patients experiencing 3 or more RFBMs per week and a 1-RFBM increase over baseline, weekly values ranged from 35% to 40% during placebo treatment; at week 5 of OLE methylnaltrexone, this percentage increased to more than 70% and remained relatively stable throughout the OLE. The most common adverse events during methylnaltrexone treatment were abdominal pain (9.7% vs 1.5% for placebo) and nausea (5.2% vs 6.7%).

Conclusions Findings during placebo treatment further establish the profile of OIC and support that little or no gastrointestinal tolerance develops across time. Findings under open-label conditions established the reproducibility and durability of methylnaltrexone for OIC.