Subcutaneous Methylnaltrexone for Treatment of Opioid-Induced Constipation in Cancer versus Noncancer Patients: An Analysis of Efficacy and Safety Variables from Two Studies

Insights into the Current and Possible Future Use of Opioid Antagonists in Relation to Opioid-Induced Constipation and Dysbiosis

Opioid receptor agonists, particularly those that activate µ-opioid receptors (MORs), are essential analgesic agents for acute or chronic mild to severe pain treatment. However, their use has raised concerns including, among others, intestinal dysbiosis. In addition, growing data on constipation-evoked intestinal dysbiosis have been reported. Opioid-induced constipation (OIC) creates an obstacle to continuing treatment with opioid analgesics. When non-opioid therapies fail to overcome the OIC, opioid antagonists with peripheral, fast first-pass metabolism, and gastrointestinal localized effects remain the drug of choice for OIC, which are discussed here. At first glance, their use seems to only be restricted to constipation, however, recent data on OIC-related dysbiosis and its contribution to the appearance of several opioid side effects has garnered a great of attention from researchers. Peripheral MORs have also been considered as a future target for opioid analgesics with limited central side effects. The properties of MOR antagonists counteracting OIC, and with limited influence on central and possibly peripheral MOR-mediated antinociception, will be highlighted. A new concept is also proposed for developing gut-selective MOR antagonists to treat or restore OIC while keeping peripheral antinociception unaffected. The impact of opioid antagonists on OIC in relation to changes in the gut microbiome is included.

Impact of Patient Subgroups on the Efficacy and Safety of Methylnaltrexone for Opioid-Induced Constipation in Patients with Advanced Illness

Purpose

We evaluated the impact of baseline patient characteristics on safety and efficacy of methylnaltrexone, a peripherally acting µ-opioid receptor antagonist, in patients with advanced illness with opioid-induced constipation (OIC).

Patients and Methods

This analysis pooled data from 2 randomized, double-blind, placebo-controlled studies (study 302: NCT00402038; study 4000: NCT00672477) in patients with advanced illness, including cancer, and OIC. Patients were randomized to receive subcutaneous methylnaltrexone (study 302: 0.15 mg/kg; study 4000: 8 or 12 mg based on weight) or placebo every other day for 2 weeks. The proportions of patients achieving rescue-free laxation within 4 or 24 hours after the first dose of study drug were assessed in patient subgroups stratified by baseline age, Eastern Cooperative Oncology Group (ECOG) performance status, cancer status, laxative type, and opioid requirement. Treatment-emergent adverse events (TEAEs) were evaluated.

Results

Overall, 363 patients were included in this analysis (methylnaltrexone, 178; placebo, 185). Mean (SD) age was 66.3 (13.7) years and 48.5% were men overall. A significantly greater proportion of patients receiving methylnaltrexone versus placebo achieved rescue-free laxation within 4 hours (111/178 [62.4%] vs 31/185 [16.8%]; P<0.0001) and 24 hours (135/178 [75.8%] vs 81/185 [43.8%]; P<0.0001) of the first dose. These trends were consistent across all subgroups. Most patients experienced ≥1 TEAE in the overall population (methylnaltrexone, 82.1%; placebo, 76.2%), which remained consistent when stratified by baseline characteristics. More than half of TEAEs were gastrointestinal in nature. Abdominal pain was more common in patients receiving methylnaltrexone than placebo across baseline characteristic subgroups.

Conclusion

Methylnaltrexone treatment was superior to placebo in achieving rescue-free laxation within 4 and 24 hours after the first dose, irrespective of patients' cancer status, baseline ECOG performance status, or baseline opioid or laxative use. The methylnaltrexone safety profile remained consistent across baseline characteristic subgroups.

Methylnaltrexone Treatment for Opioid-Induced Constipation in Patients with and without Cancer: Effect of Initial Dose

Purpose

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.

Patients and Methods

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.

Results

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%, p<0.0001; noncancer: MNTX, 62.2% vs placebo, 17.5%, p<0.0001) and 24 hours (cancer: MNTX, 71.2% vs placebo, 41.4%, p<0.0001; noncancer: MNTX, 74.4% vs placebo, 37.5%, p<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.

Conclusion

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.

Endogenous opiates and behavior: 2021

This paper is the forty-fourth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2021 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonizts and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Subcutaneous Methylnaltrexone as Treatment for Opioid-Induced Constipation in Patients with Advanced Cancer and Noncancer Illnesses: A Post Hoc Analysis of Two Clinical Trials

Purpose

To evaluate the efficacy and safety of subcutaneous (SC) methylnaltrexone for opioid-induced constipation (OIC) in patients with and without active cancer.

Patients and Methods

We analyzed two randomized, double-blind, placebo-controlled, Phase 3/4 trials (NCT00402038, NCT00672477). Patients received SC methylnaltrexone (study 302, 0.15 mg/kg; study 4000, 8 mg or 12 mg based on body weight) or placebo every other day for 2 weeks. Patients were stratified by cancer status. Primary efficacy endpoints included proportion of patients achieving rescue-free laxation (RFL); secondary endpoints included time to RFL, pain intensity scores, and safety/tolerability. Trial results were evaluated separately.

Results

The safety population (patients receiving ≥1 study drug dose) included 364 patients (study 302, n=134; study 4000, n=230). Study 302 had 78 patients with active cancer (methylnaltrexone, n=37; placebo, n=41) and 56 without cancer (methylnaltrexone, n=26; placebo, n=30); study 4000 had 152 patients with active cancer (methylnaltrexone, n=79; placebo, n=73) and 78 without cancer (methylnaltrexone, n=37; placebo, n=41). A significantly greater proportion of patients treated with methylnaltrexone achieved a laxation response within 4 hours after at least 2 of the first 4 doses versus placebo, dosed by body weight (cancer, 54.1% [methylnaltrexone] vs 7.3% [placebo], P<0.0001; noncancer, 48.0% vs 10.0%; P<0.005) or given as a weight-adjusted fixed dose (cancer, 59.5% vs 6.8%; noncancer, 70.3% vs 14.6%; P<0.0001 each). With fixed-dose methylnaltrexone, average time to RFL for patients with and without cancer was <1 hour of the first dose; with methylnaltrexone dosed by body weight, the first RFL occurred in <4 and <7 hours of treatment in patients with and without cancer, respectively. No significant differences were found in pain scores. SC methylnaltrexone was well tolerated at all doses in all patient cohorts.

Conclusion

SC methylnaltrexone was efficacious in inducing rapid RFL and safe among patients with and without active cancer suffering from OIC.