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PurposePeripherally acting μ-opioid receptor antagonists such as methylnaltrexone (MNTX, Relistor®) are indicated for the treatment of opioid-induced constipation (OIC). The structural properties unique to MNTX restrict it from traversing the blood-brain barrier (BBB); however, the BBB may become more permeable in patients with brain metastases. We investigated whether the presence of brain metastases in cancer patients compromises the central effects of opioids among patients receiving MNTX for OIC.MethodsThis post hoc analysis of pooled data from 3 randomized, placebo-controlled trials included cancer patients with OIC who received MNTX or placebo. Endpoints included changes from baseline in pain scores, rescue-free laxation (RFL) within 4 or 24 h of the first dose, and treatment-emergent adverse events (TEAEs), including those potentially related to opioid withdrawal symptoms.ResultsAmong 356 cancer patients in the pooled population, 47 (MNTX n = 27; placebo n = 20) had brain metastases and 309 (MNTX n = 172; placebo n = 137) did not have brain metastases. No significant differences in current pain, worst pain, or change in pain scores from baseline were observed between patients treated with MNTX or placebo. Among patients with brain metastases, a significantly greater proportion of patients who received MNTX versus placebo achieved an RFL within 4 h after the first dose (70.4% vs 15.0%, respectively, p = 0.0002). TEAEs were similar between treatment groups and were generally gastrointestinal in nature and not related to opioid withdrawal.ConclusionFocal disruptions of the BBB caused by brain metastases did not appear to alter central nervous system penetrance of MNTX.

Background: Opioids prescribed for the management of chronic noncancer pain are associated with nausea, vomiting, and constipation. Methylnaltrexone, a peripherally acting µ-opioid receptor antagonist, has demonstrated robust efficacy and was well-tolerated in treating opioid-induced constipation without affecting central analgesia. Our objective was to assess changes in the frequency of adverse events after the first or second dose of methylnaltrexone or placebo. Methods: This post hoc analysis pooled data from two randomized, placebo-controlled clinical trials assessing methylnaltrexone for opioid-induced constipation in the outpatient setting. Patients received subcutaneous methylnaltrexone (12 mg once daily or 12 mg once every other day), oral methylnaltrexone (150, 300, or 450 mg daily), or placebo. Adverse events, opioid withdrawal symptoms, pain intensity, and rescue-free bowel movements (RFBMs) within 4 hours of the first dose (i.e., RFBM responders) were assessed. Associations between adverse event frequencies and RFBM response were also evaluated. Results: The analysis included 1263 adult patients with chronic noncancer pain. Treatment-emergent adverse event rates declined from treatment day 1 to 2 (methylnaltrexone: 16.2%-5.3%; placebo: 6.6%−5.4%). Among methylnaltrexone-treated patients, significantly greater proportions of RFBM responders versus nonresponders reported gastrointestinal adverse events on day 1. No associations between RFBM response and the frequency of adverse events were observed in the placebo group. No meaningful changes in opioid withdrawal symptoms or pain intensity were observed. Conclusions: Early-onset adverse events following methylnaltrexone treatment, particularly gastrointestinal adverse events, are at least partially due to laxation. Methylnaltrexone treatment effectively relieves opioid-induced constipation without affecting the central analgesic effects of opioids.

Background: Opioids prescribed for the management of chronic noncancer pain are associated with nausea, vomiting, and constipation. Methylnaltrexone, a peripherally acting µ-opioid receptor antagonist, has demonstrated robust efficacy and was well-tolerated in treating opioid-induced constipation without affecting central analgesia. Our objective was to assess changes in the frequency of treatment-emergent adverse events (TEAEs) after the first or second dose of methylnaltrexone or placebo. Methods: This post hoc analysis pooled data from two randomized, placebo-controlled clinical trials assessing methylnaltrexone for opioid-induced constipation in the outpatient setting. Patients received subcutaneous methylnaltrexone (12 mg once daily or 12 mg once every other day), oral methylnaltrexone (150, 300, or 450 mg daily), or placebo. TEAEs, opioid withdrawal symptoms, pain intensity, and rescue-free bowel movements (RFBMs) within 4 hours of the first dose (i.e., RFBM responders) were assessed. Associations between TEAE frequencies and RFBM response were also evaluated. Results: The analysis included 1263 adult patients with chronic noncancer pain. TEAE rates declined from treatment day 1 to 2 (methylnaltrexone: 16.2%-5.3%; placebo: 6.6%−5.4%). Among methylnaltrexone-treated patients, significantly greater proportions of RFBM responders versus nonresponders reported gastrointestinal TEAEs on day 1. No associations between RFBM response and the frequency of TEAEs were observed in the placebo group. No meaningful changes in opioid withdrawal symptoms or pain intensity were observed. Conclusions: Early-onset TEAEs following methylnaltrexone treatment, particularly gastrointestinal TEAEs, are at least partially due to laxation. Methylnaltrexone treatment effectively relieves opioid-induced constipation without affecting the central analgesic effects of opioids.

This study investigated the safety and efficacy of subcutaneous methylnaltrexone, a μ-opioid–receptor antagonist, for treating opioid-induced constipation in patients with advanced illness. Methylnaltrexone rapidly induced laxation without affecting central analgesia or precipitating withdrawal. This study investigated the safety and efficacy of subcutaneous methylnaltrexone for treating opioid-induced constipation in patients with advanced illness. Methylnaltrexone rapidly induced laxation without affecting central analgesia or precipitating withdrawal. Clinicians often use opioids to treat moderate-to-severe pain; however, opioids frequently induce or aggravate constipation. Empirically, laxative therapy may be burdensome and ineffective and result in temporally unpredictable responses. In addition, severe opioid-induced constipation may limit opioid therapy, worsening analgesia. These drawbacks can substantially compromise the quality of life, especially in patients with advanced illness. Opioid-induced constipation is predominantly mediated by gastrointestinal μ-opioid receptors. 1 , 2 Selective blockade of these peripheral receptors might relieve constipation without compromising centrally mediated effects of opioid analgesia or precipitating withdrawal. N-methylation of the uncharged systemic opioid antagonist, naltrexone, 3 results in a charged derivative, methylnaltrexone, which . . .

A correction to this paper has been published: https://doi.org/10.1007/s40266-021-00860-8

Background Methylnaltrexone, a peripherally acting µ-opioid receptor antagonist approved for the treatment of opioid-induced constipation (OIC), has restricted diffusion across the blood–brain barrier (BBB) and has not been demonstrated to impact opioid-induced central analgesia. Age-related changes in BBB permeability may compromise methylnaltrexone’s restricted diffusion and alter opioid-induced central analgesic effects. Objective This analysis evaluated whether opioid analgesia is compromised in older adults receiving methylnaltrexone for OIC. Methods The analysis included adults diagnosed with OIC who received opioids for pain management and who had a terminal illness or chronic nonmalignant pain. Data were pooled from four randomized, double-blind trials and stratified by age (< 65 years and ≥ 65 years). Endpoints included pain intensity scores, symptoms of opioid withdrawal, treatment-related adverse events (TRAEs), and rescue-free laxation (RFL) within 4 h of treatment. Results Overall, 1323 patients were < 65 years of age ( n =  908, methylnaltrexone; n =  415, placebo) and 304 patients were ≥ 65 years of age ( n =  171, methylnaltrexone; n =  133, placebo). Nonsignificant pain intensity score reductions were observed in all groups. In the older cohort, measures of opioid withdrawal did not show statistical differences from baseline in either the methylnaltrexone or placebo groups. The most frequently reported TRAEs were abdominal pain, flatulence, and nausea. Relative to the first dose, gastrointestinal TRAEs potentially related to opioid withdrawal declined with the second dose and were comparable with placebo, regardless of age. RFL response within 4 h of methylnaltrexone treatment increased significantly in both age cohorts relative to placebo. Conclusions Methylnaltrexone use did not adversely affect pain control, opioid withdrawal effects, or AEs while providing effective RFL, regardless of age. These results suggest that age does not appear to influence the safety and efficacy of methylnaltrexone for OIC. Further research is needed to assess the impact of other factors that alter BBB permeability, such as dementia, stroke, or drug interactions, on the safety and efficacy of methylnaltrexone. Clinical Trial Registration Numbers Study 302, NCT00402038; study 3200K1-4000, NCT00672477; study 3200K1-3356, NCT00529087; study 3201, NCT01186770.

Objective Preclinical and clinical studies suggest that activation of the µ-opioid receptor may reduce overall survival and increase the risk for all-cause mortality in patients with cancer and noncancer pain. Methylnaltrexone, a selective, peripherally acting µ-opioid receptor antagonist, has demonstrated efficacy for the treatment of opioid-induced constipation. This retrospective analysis of 12 randomized, double-blind, placebo-controlled studies of methylnaltrexone evaluated the treatment of opioid-induced bowel disorders in patients with advanced illness or noncancer pain. Methods The risk of all-cause mortality within 30 days after the last dose of study medication during the double-blind phase was compared between methylnaltrexone and placebo groups. The data were further stratified by cancer vs noncancer, age, gender, and acute vs chronic diagnoses. Results Pooled data included 2,526 methylnaltrexone-treated patients of which 33 died, and 1,192 placebo-treated patients of which 35 died. The mortality rate was 17.8 deaths/100 person-years of exposure in the methylnaltrexone group and 49.5 deaths/100 person-years of exposure for the placebo group. The all-cause mortality risk was significantly lower among patients receiving methylnaltrexone compared with placebo (hazard ratio: 0.399, 95% confidence interval: 0.25, 0.64; P = .0002), corresponding to a 60% risk reduction. Significant risk reductions were observed for those receiving methylnaltrexone who had cancer or chronic diagnoses. Methylnaltrexone-treated patients had a significantly reduced mortality risk compared with placebo regardless of age or gender. Conclusions Methylnaltrexone reduced all-cause mortality vs placebo treatment across multiple trials, suggesting methylnaltrexone may confer survival benefits in patients with opioid-induced bowel disorders taking opioids for cancer-related or chronic noncancer pain.

Opioid-induced constipation (OIC) is a common side effect of opioid therapy. Methylnaltrexone (MNTX) is a selective, peripherally acting μ-opioid receptor antagonist, with demonstrated efficacy in treating OIC. We pooled results from MNTX clinical trials to compare responses to an initial dose in patients with chronic cancer and noncancer pain. This post hoc analysis used pooled data from 3 randomized, placebo-controlled studies of MNTX in patients with advanced illness with OIC. Assessments included the proportions of patients achieving rescue-free laxation (RFL) within 4 and 24 hours of the first study drug dose, time to RFL, current and worst pain intensity, and adverse events, stratified by the presence/absence of cancer. A total of 355 patients with cancer (MNTX n = 198, placebo n = 157) and 163 without active cancer (MNTX n = 83; placebo n = 80) were included. More patients treated with MNTX compared with those who received placebo achieved an RFL within 4 (cancer: MNTX, 61.1% vs placebo,15.3%, <0.0001; noncancer: MNTX, 62.2% vs placebo, 17.5%, <0.0001) and 24 hours (cancer: MNTX, 71.2% vs placebo, 41.4%, <0.0001; noncancer: MNTX, 74.4% vs placebo, 37.5%, <0.0001) of the initial dose. Cumulative RFL response rates within 4 hours of the first, second, or third dose of study drug were also higher in MNTX-treated patients. The estimated time to RFL was shorter among those who received MNTX and similar in cancer and noncancer patients. Mean pain scores declined similarly in all groups. The most common adverse events in both cancer and noncancer patients were abdominal pain, flatulence, and nausea. After the first dose, MNTX rapidly induced a laxation response in the majority of both cancer and noncancer patients with advanced illness. Opioid-induced analgesia was not compromised, and adverse events were primarily gastrointestinal in nature. Methylnaltrexone is a well-tolerated and effective treatment for OIC in both cancer and noncancer patients.