Methylnaltrexone for the treatment of opioid-induced constipation

Mu-opioid antagonists for opioid-induced bowel dysfunction in people with cancer and people receiving palliative care

BACKGROUND

Opioid-induced bowel dysfunction (OIBD) is characterised by constipation, incomplete evacuation, bloating, and gastric reflux. It is one of the major adverse events (AEs) of treatment for pain in cancer and palliative care, resulting in increased morbidity and reduced quality of life. This review is a partial update of a 2008 review, and critiques as previous update (2018) trials only for people with cancer and people receiving palliative care.

OBJECTIVES

To assess for OIBD in people with cancer and people receiving palliative care the effectiveness and safety of mu-opioid antagonists (MOAs) versus different doses of MOAs, alternative pharmacological/non-pharmacological interventions, placebo, or no treatment.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, CINAHL, and Web of Science (December 2021), clinical trial registries and regulatory websites. We sought contact with MOA manufacturers for further data.

SELECTION CRITERIA

Randomised controlled trials (RCTs) assessing the effectiveness and safety of MOAs for OIBD in people with cancer and people at a palliative stage irrespective of the type of terminal disease.

DATA COLLECTION AND ANALYSIS

Two review authors assessed risk of bias and extracted data. The appropriateness of combining data from the trials depended upon sufficient homogeneity across trials. Our primary outcomes were laxation response, effect on analgesia, and AEs. We assessed the certainty of evidence using GRADE and created summary of findings tables.

MAIN RESULTS

We included 10 studies (two new trials) randomising in-total 1343 adults with cancer irrespective of stage, or at palliative care stage of any disease. The MOAs were oral naldemedine and naloxone (alone or in combination with oxycodone), and subcutaneous methylnaltrexone. The trials compared MOAs with placebo, MOAs at different doses, or in combination with other drugs. Two trials of naldemedine and three of naloxone with oxycodone were in people with cancer irrespective of disease stage. The trial on naloxone alone was in people with advanced cancer. Four trials on methylnaltrexone were in palliative care where most participants had advanced cancer. All trials were vulnerable to biases; most commonly, blinding of the outcome assessor was not reported.  Oral naldemedine versus placebo Risk (i.e. chance) of spontaneous laxations in the medium term (over two weeks) for naldemedine was over threefold greater risk ratio (RR) 2.00, 95% confidence interval (CI) 1.59 to 2.52, 2 trials, 418 participants, I² = 0%. Number needed to treat for an additional beneficial outcome (NNTB) 3, 95% CI 3 to 4; moderate-certainty evidence). Earlier risk of spontaneous laxations and patient assessment of bowel change was not reported. Very low-certainty evidence showed naldemedine had little to no effect on opioid withdrawal symptoms. There was little to no difference in the risk of serious (non-fatal) AEs (RR 3.34, 95% CI 0.85 to 13.15: low-certainty evidence). Over double the risk of AEs (non-serious) reported with naldemedine (moderate-certainty evidence). Low-dose oral naldemedine versus higher dose Risk of spontaneous laxations was lower for the lower dose (medium term, 0.1 mg versus 0.4 mg: RR 0.69, 95% CI 0.53 to 0.89, 1 trial, 111 participants (low-certainty evidence)). Earlier risk of spontaneous laxations and patient assessment of bowel change not reported. Low-certainty evidence showed little to no difference on opioid withdrawal symptoms (0.1 mg versus 0.4 mg mean difference (MD) -0.30, 95% CI -0.85 to 0.25), and occurrences of serious AEs (0.1 mg versus 0.4 mg RR 0.25, 95% CI 0.03 to 2.17). Low-certainty evidence showed little to no difference on non-serious AEs. Oral naloxone versus placebo Risk of spontaneous laxations and AEs not reported. Little to no difference in pain intensity (very low-certainty evidence). Full data not given. The trial reported that no serious AEs occurred. Oral naloxone + oxycodone versus oxycodone Risk of spontaneous laxations within 24 hours and in the medium term not reported. Low-certainty evidence showed naloxone with oxycodone reduced the risk of opioid withdrawal symptoms. There was little to no difference in the risk of serious (non-fatal) AEs (RR 0.68, 95% CI 0.44 to 1.06), 3 trials, 362 participants, I² = 55%: very low-certainty evidence). There was little to no difference in risk of AEs (low-certainty evidence).  Subcutaneous methylnaltrexone versus placebo Risk of spontaneous laxations within 24 hours with methylnaltrexone was fourfold greater than placebo (RR 2.97, 95% CI 2.13 to 4.13. 2 trials, 287 participants, I² = 31%. NNTB 3, 95% CI 2 to 3; low-certainty evidence). Risk of spontaneous laxations in the medium term was over tenfold greater with methylnaltrexone (RR 8.15, 95% CI 4.76 to 13.95, 2 trials, 305 participants, I² = 47%. NNTB 2, 95% CI 2 to 2; moderate-certainty evidence). Low-certainty evidence showed methylnaltrexone reduced the risk of opioid withdrawal symptoms, and did not increase risk of a serious AE (RR 0.59, 95% CI 0.38 to 0.93. I² = 0%; 2 trials, 364 participants). The risk of AEs was higher for methylnaltrexone (low-certainty evidence). Lower-dose subcutaneous methylnaltrexone versus higher dose There was little to no difference in risk of spontaneous laxations in the medium-term (1 mg versus 5 mg or greater: RR 2.91, 95% CI 0.82 to 10.39; 1 trial, 26 participants very low-certainty evidence), or in patient assessment of improvement in bowel status (RR 0.98, 95% CI 0.71 to 1.35, 1 trial, 102 participants; low-certainty evidence). Medium-term assessment of spontaneous laxations and serious AEs not reported. There was little to no difference in symptoms of opioid withdrawal (MD -0.25, 95% CI -0.84 to 0.34, 1 trial, 102 participants) or occurrence of AEs (low-certainty evidence).

AUTHORS' CONCLUSIONS

This update's findings for naldemedine and naloxone with oxycodone have been strengthened with two new trials, but conclusions have not changed. Moderate-certainty evidence for oral naldemedine on risk of spontaneous laxations and non-serious AEs suggests in people with cancer that naldemedine may improve bowel function over two weeks and increase the risk of AEs. There was low-certainty evidence on serious AEs. Moderate-certainty evidence for methylnaltrexone on spontaneous laxations over two weeks suggests subcutaneous methylnaltrexone may improve bowel function in people receiving palliative care, but certainty of evidence for AEs was low. More trials are needed, more evaluation of AEs, outcomes patients rate as important, and in children.

Repurposing FDA-approved drugs against multiple proteins of SARS-CoV-2: An in silico study

The current crisis of the COVID-19 pandemic around the world has been devastating as many lives have been lost to the novel SARS CoV-2 virus. Thus, there is an urgent need for the right therapeutic drug to curb the disease. However, there is time constraint in drug development, hence the need for drug repurposing approach, a relatively fast and less expensive alternative. In this study, 1,100 Food and Drug Administration (FDA) approved drugs were obtained from DrugBank and trimmed to 791 ligands based on illicitness, withdrawal from the market, being chemical agents rather than drugs, being investigational drugs and having molecular weight greater than 500 (Kg/mol). The ligands were docked against six drug targets of the novel SARS CoV-2 - 3-chymotrypsin-like protease (3CLpro), Angiotensin-converting enzyme (ACE2), ADP ribose phosphatase of NSP3 (NSP3), NSP9 RNA binding protein (NSP9), RNA dependent RNA polymerase (RdRp) and Replicase Polyprotein 1a (RP1a). UCSF Chimera, PyRx and Discovery Studio, were used to prepare the proteins, dock the ligands and visualize the complexes, respectively. Remdesivir, Lopinavir and Hydroxychloroquine were used as reference drugs. Pharmacokinetic properties of the ligands were obtained using AdmetSAR. The binding energies of the standard drugs ranged from -5.4 to -8.7 kcal/mol while over 400 of the ligands screened showed binding energy lower than -5.4 kcal/mol. Out of the 791 number of compounds docked, 10, 91, 132, 92, 54 and 96 compounds showed lower binding energies than all the controls against 3CLPro, ACE2, NSP3, NSP9, RP1a and RdRp, respectively. Ligands that bound all target proteins, and showed the lowest binding energies with good ADMET properties and particularly showed the lowest binding against ACE2 are ethynodiol diacetate (-15.6 kcal/mol), methylnaltrexone (-15.5 kcal/mol), ketazolam (-14.5 kcal/mol) and naloxone (-13.6 kcal/mol). Further investigations are recommended for ethynodiol diacetate, methylnaltrexone, ketazolam and naloxone through preclinical and clinical studies to ascertain their effectiveness.

Experimental considerations for the assessment of in vivo and in vitro opioid pharmacology

Morphine and other mu-opioid receptor (MOR) agonists remain the mainstay treatment of acute and prolonged pain states worldwide. The major limiting factor for continued use of these current opioids is the high incidence of side effects that result in loss of life and loss of quality of life. The development of novel opioids bereft, or much less potent, at inducing these side effects remains an intensive area of research, with multiple pharmacological strategies being explored. However, as with many G protein-coupled receptors (GPCRs), translation of promising candidates from in vitro characterisation to successful clinical candidates still represents a major challenge and attrition point. This review summarises the preclinical animal models used to evaluate the key opioid-induced behaviours of antinociception, respiratory depression, constipation and opioid-induced hyperalgesia and tolerance. We highlight the influence of distinct variables in the experimental protocols, as well as the potential implications for differences in receptor reserve in each system. Finally, we discuss how methods to assess opioid action in vivo and in vitro relate to each other in the context of bridging the translational gap in opioid drug discovery.

Methylnaltrexone and Naloxone for Opioid-induced Constipation in the Critical Care Setting

Opioid antagonists in the ICU are often a last-line medication given to patients with opioid-induced constipation. Traditionally, patients have been administered nonopioid-based bowel regimens such as senna, peg, and docusate to treat constipation. Despite the obvious need to treat acute pain with opioids, side effects such as constipation can lead to multiple gastrointestinal (GI) complications such as bowel perforation and even death. Specifically, opioid-induced constipation (OIC) can be very difficult to treat. We examine naloxone and methylnaltrexone (MNTX) assessing GI complications and OIC as well as present a patient case which highlights the importance of treating OIC. We also evaluate the superior reversal agent of choice when treating OIC in the critical care and stepdown unit settings.

The role of oxycodone/naloxone in the management of patients with pain and opioid-induced constipation

INTRODUCTION

Common opioid adverse effects (AE) of the gastrointestinal tract include opioid-induced constipation (OIC) and opioid-induced bowel dysfunction (OIBD) with traditional laxatives being of limited efficacy, having AEs and not addressing the pathophysiology of OIC or OIBD. Targeted treatment comprises of PAMORA (peripherally acting mu-opioid receptor antagonists) and a combination of an opioid receptor agonist with its antagonist, namely prolonged-release oxycodone with prolonged-release naloxone (OXN) tablets at a fixed ratio of 2:1. Oxycodone provides analgesia, whereas naloxone prevents binding or displaces it from opioid receptors located in the gut wall. Areas covered: The authors review the role of OXN in the management of patients with pain and OIC. A literature search was performed using the search terms 'oxycodone/naloxone' and 'opioid-induced constipation' using the PubMed database up to October 2018. Expert opinion: OXN delivers analgesia comparable (or superior versus placebo and in observational studies) to oxycodone alone and other opioids with a limited or decreased disturbing effect on bowel function. OXN in daily doses of up to 160 mg/80 mg provides effective analgesia with little negative impact on bowel function. OXN may be successfully used in patients with chronic pain, to prevent or treat symptoms of OIC and OIBD.

Mu-opioid antagonists for opioid-induced bowel dysfunction in people with cancer and people receiving palliative care

BACKGROUND

Opioid-induced bowel dysfunction (OIBD) is characterised by constipation, incomplete evacuation, bloating, and gastric reflux. It is one of the major adverse events of treatment for pain in cancer and in palliative care, resulting in increased morbidity and reduced quality of life.This is an update of two Cochrane reviews. One was published in 2011, Issue 1 on laxatives and methylnaltrexone for the management of constipation in people receiving palliative care; this was updated in 2015 and excluded methylnaltrexone. The other was published in 2008, Issue 4 on mu-opioid antagonists (MOA) for OIBD. In this updated review, we only included trials on MOA (including methylnaltrexone) for OIBD in people with cancer and people receiving palliative care.

OBJECTIVES

To assess the effectiveness and safety of MOA for OIBD in people with cancer and people receiving palliative care.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials, MEDLINE, Embase, CINAHL, and Web of Science to August 2017. We also searched clinical trial registries and regulatory websites. We contacted manufacturers of MOA to identify further data.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that assessed the effectiveness and safety of MOA for OIBD in people with cancer and people at a palliative stage irrespective of the type of terminal disease they experienced.

DATA COLLECTION AND ANALYSIS

Two review authors assessed risk of bias and extracted data. The appropriateness of combining data from the trials depended upon sufficient homogeneity across the trials. Our primary outcomes were laxation, impact on pain relief, and adverse events. Impact on pain relief was a primary outcome because a possible adverse effect of MOAs is a reduction in pain relief from opioids. We assessed the evidence on these outcomes using GRADE.

MAIN RESULTS

We identified four new trials for this update, bringing the total number included in this review to eight. In total, 1022 men and women with cancer irrespective of stage or at a palliative care stage of any disease were randomised across the trials. The MOAs evaluated were oral naldemedine and naloxone (alone or in combination with oxycodone), and subcutaneous methylnaltrexone. The trials compared with MOA with a placebo or with the active intervention administered at different doses or in combination with other drugs. The trial of naldemedine and the two of naloxone in combination with oxycodone were in people with cancer irrespective of disease stage. The trial on naloxone alone was in people with advanced cancer. The four trials on methylnaltrexone were undertaken in palliative care where most participants had cancer. All trials were vulnerable to biases; four were at a high risk as they involved a sample of fewer than 50 participants per arm.In the trial of naldemedine compared to placebo in 225 participants, there were more spontaneous laxations over the two-week treatment for the intervention group (risk ratio (RR) 1.93, 95% confidence intervals (CI) 1.36 to 2.74; moderate-quality evidence). In comparison with higher doses, lower doses resulted in fewer spontaneous laxations (0.1 mg versus 0.2 mg: RR 0.73, 95% CI 0.55 to 0.95; 0.1 mg versus 0.4 mg: RR 0.69, 95% CI 0.53 to 0.89; moderate-quality evidence). There was moderate-quality evidence that naldemedine had no effect on opiate withdrawal. There were five serious adverse events. All were in people taking naldemedine (low-quality evidence). There was an increase in the occurrence of other (non-serious) adverse events in the naldemedine groups (RR 1.36, 95% CI 1.04 to 1.79, moderate-quality evidence). The most common adverse event was diarrhoea.The trials on naloxone taken either on its own, or in combination with oxycodone (an opioid) compared to oxycodone only did not evaluate laxation response over the first two weeks of administration. There was very low-quality evidence that naloxone alone, and moderate-quality evidence that oxycodone/naloxone, had no effect on analgesia. There was low-quality evidence that oxycodone/naloxone did not increase the risk of serious adverse events and moderate-quality evidence that it did not increase risk of adverse events.In combined analysis of two trials of 287 participants, we found methylnaltrexone compared to placebo induced more laxations within 24 hours (RR 2.77, 95% CI 1.91 to 4.04. I² = 0%; moderate-quality evidence). In combined analysis, we found methylnaltrexone induced more laxation responses over two weeks (RR 9.98, 95% CI 4.96 to 20.09. I² = 0%; moderate-quality evidence). The proportion of participants who had a rescue-free laxation response within 24 hours of the first dose was 59.1% in the methylnaltrexone arms and 19.1% in the placebo arm. There was moderate-quality evidence that the rate of opioid withdrawal was not affected. Methylnaltrexone did not increase the likelihood of a serious adverse event; there were fewer in the intervention arm (RR 0.59, 95% CI 0.38 to 0.93; I² = 0%; moderate-quality evidence). There was no difference in the proportion of participants experiencing an adverse event (RR 1.17, 95% CI 0.94 to 1.45; I² = 74%; low-quality evidence). Methylnaltrexone increased the likelihood of abdominal pain and flatulence.Two trials compared differing methylnaltrexone schedules of higher doses with lower doses. For early laxation, there was low-quality evidence of no clear difference between doses on analgesia and adverse events. Both trials measured laxation response within 24 hours of first dose (trial one: RR 0.82, 95% CI 0.41 to 1.66; trial two: RR 1.07, 95% CI 0.81 to 1.42).

AUTHORS' CONCLUSIONS

In this update, the conclusions for naldemedine are new. There is moderate-quality evidence to suggest that, taken orally, naldemedine improves bowel function over two weeks in people with cancer and OIBD but increases the risk of adverse events. The conclusions on naloxone and methylnaltrexone have not changed. The trials on naloxone did not assess laxation at 24 hours or over two weeks. There is moderate-quality evidence that methylnaltrexone improves bowel function in people receiving palliative care in the short term and over two weeks, and low-quality evidence that it does not increase adverse events. There is a need for more trials including more evaluation of adverse events. None of the current trials evaluated effects in children.

Long-Term Safety and Efficacy of Subcutaneous Methylnaltrexone in Patients with Opioid-Induced Constipation and Chronic Noncancer Pain: A Phase 3, Open-Label Trial

Objective. Methylnaltrexone, a peripherally acting µ-opioid receptor antagonist, alleviates opioid-induced constipation. Understanding its long-term safety and efficacy profile in patients with chronic noncancer pain is warranted given the persistence of opioid-induced constipation.

Methods. In this phase 3, multicenter, open-label trial, adults with chronic noncancer pain (N = 1034) received subcutaneous methylnaltrexone 12 mg once daily for 48 weeks.

Results. The most common adverse events were gastrointestinal related (e.g., abdominal pain, diarrhea, nausea) and were mild to moderate in intensity. Only 15.2% of patients discontinued because of an adverse event. Serious cardiac-related adverse events occurred in nine patients. Of the seven instances of major adverse coronary events reported, three were adjudicated after external review; all instances occurred in patients with cardiovascular risk factors. Methylnaltrexone elicited a bowel movement within four hours in 34.1% of the injections throughout the 48-week treatment period.

Conclusions. Change from baseline in mean weekly bowel movement rate, Bowel Movement Straining Scale score, Bristol Stool Scale score, and mean percentage of patients with complete evacuation from baseline to week 48 were significantly improved (P < 0.001 for all). Long-term subcutaneous methylnaltrexone was well tolerated, with no new safety concerns, and provided consistent opioid-induced constipation relief in patients with chronic noncancer pain.

A concise review of opioid-induced esophageal dysfunction: is this a new clinical entity?

Opioids have become the most widely prescribed analgesics in Western countries. Opioid-induced bowel dysfunction is a widely known adverse effect, with constipation the most common manifestation. Most of the opioid-related effects occur in the stomach, small intestine, and colon and have been widely studied. However, the effects related to esophageal motility are less known. Recently published retrospective studies have suggested that long-term use of opioids can cause esophageal motility dysfunction, reflecting symptoms similar to motility disorders, such as achalasia and functional esophagogastric junction outflow obstruction. The most common manometric findings, as reported in the literature, for patients with opioid-induced dysphagia undergoing long-term therapy with these drugs are impaired lower esophageal sphincter relaxation, high amplitude/velocity, and simultaneous esophageal waves, higher integrated relaxation pressure, lower distal latency, and the esophageal contractility can be normal, hypercontractile, or premature. Based on these studies, a new clinical entity known as opioid-induced esophageal dysfunction has been postulated. For these patients, the diagnostic method of choice is high-resolution manometry, although other causes should be ruled out through endoscopy or Computed Tomography (CT). The best therapeutic option for these patients is withdrawal of the opioid; however, this is not always possible, and other options need to be investigated, such as pneumatic dilation and botulinum toxin injection, considering the risks versus the benefits.

Insights into the Role of Opioid Receptors in the GI Tract: Experimental Evidence and Therapeutic Relevance

Opioid drugs are prescribed extensively for pain treatment but when used chronically they induce constipation that can progress to opioid-induced bowel dysfunction. Opioid drugs interact with three classes of opioid receptors: mu opioid receptors (MORs), delta opioid receptors (DOR), and kappa opioid receptors (KORs), but opioid drugs mostly target the MORs. Upon stimulation, opioid receptors couple to inhibitory Gi/Go proteins that activate or inhibit downstream effector proteins. MOR and DOR couple to inhibition of adenylate cyclase and voltage-gated Ca2+ channels and to activation of K+ channels resulting in reduced neuronal activity and neurotransmitter release. KORs couple to inhibition of Ca2+ channels and neurotransmitter release. In the gastrointestinal tract, opioid receptors are localized to enteric neurons, interstitial cells of Cajal, and immune cells. In humans, MOR, DOR, and KOR link to inhibition of acetylcholine release from enteric interneurons and motor neurons and purine/nitric oxide release from inhibitory motor neurons causing inhibition of propulsive motility patterns. MOR and DOR activation also results in inhibition of submucosal secretomotor neurons reducing active Cl- secretion and passive water movement into the colonic lumen. Together, these effects on motility and secretion account for the constipation caused by opioid receptor agonists. Tolerance develops to the analgesic effects of opioid receptor agonists but not to the constipating actions. This may be due to differences in trafficking and downstream signaling in enteric nerves in the colon compared to the small intestine and in neuronal pain pathways. Further studies of differential opioid receptor desensitization and tolerance in subsets of enteric neurons may identify new drug or other treatment strategies of opioid-induced bowel dysfunction.

Methylnaltrexone for opioid-induced constipation: review and meta-analyses for objective plus subjective efficacy and safety outcomes

Introduction

Opioid-induced constipation (OIC) is a frequent adverse event that impairs patients’ quality of life. This article evaluates the objective plus subjective efficacy and the safety of methylnaltrexone (MNTX) in OIC patients.

Methods

Randomized controlled trials from a recent systematic review were included. In addition, a PubMed search was conducted for January 2014 to December 21, 2015. We included randomized controlled trials with adult OIC patients, MNTX as study drug, and OIC as primary outcome. Results were categorized in three outcome types: objective outcome measures (eg, time to laxation), patient-reported outcomes (eg, straining), and global burden measures (eg, constipation distress). Dichotomous meta-analyses with risk ratios (RRs) and 95% confidence intervals (CIs) were calculated using RevMan 5.3. Only comparisons between MNTX and placebo were made.

Results

We included seven studies with 1,860 patients. A meta-analysis revealed that patients under MNTX had considerably more rescue-free bowel movement within 4 hours after the first dose (RR 3.74, 95% CI 2.87 to 4.86; five studies, n=938; I²=0). Results of the review indicated that patients under MNTX had a higher stool frequency and needed less time to laxation compared with placebo. Moreover, patients receiving MNTX tended to have better values in patient-reported outcomes and global burden measures. Meta-analyses on safety revealed that patients under MNTX experienced more abdominal pain (RR 2.38, 95% CI 1.75 to 3.23; six studies, n=1,412; I²=60%) but showed a nonsignificant tendency in nausea (RR 1.27, 95% CI 0.90 to 1.78; six studies, n=1,412; I²=12%) and diarrhea (RR 1.45, 95% CI 0.94 to 2.24; five studies, n=1,258; I²=45%). The incidence of MNTX-related serious adverse events was 0.2% (4/1,860).

Conclusion

MNTX has been shown to be effective and safe. Future randomized controlled trials should consequently incorporate objective outcome measures, patient-reported outcomes, and global burden measures, and research the efficacy of MNTX in other populations, for example, patients under opioids after surgical procedures.

Opioid-induced constipation in chronic noncancer pain

PURPOSE OF REVIEW

Opioid-based management of noncancer pain has become much more prevalent over the last 2 decades and is responsible for a wide range of side-effects, particularly affecting the intestinal tract causing opioid-induced constipation (OIC). This review will consider results of recent clinical trials that have provided evidence of new pharmacological management options for the treatment of OIC.

RECENT FINDINGS

Supportive use of conventional agents, such as stool softeners, osmotic laxatives, and stimulating laxatives in OIC has limited efficacy. The peripheral μ-opioid receptor antagonist (PAMORA) methylnaltrexone (MNTX) was first FDA approved for OIC in patients with advanced illness and later also for OIC in noncancer pain patients; clinical trial results indicated MNTX did not reverse opioid analgesia and did not trigger central opioid withdrawal. Another PAMORA, the orally available naloxegol, has also gained recent FDA approval for the treatment of OIC in adults with chronic, noncancer pain. Lubiprostone, a bicyclical fatty acid acting via activation of intestinal chloride channel-2 (ClC-2), was also approved for OIC treatment in patients with noncancer pain.

SUMMARY

PAMORA MNTX and naloxegol and the intestinal chloride channel-2 (ClC-2) activator lubiprostone represent additional possible therapeutic options for the management of OIC in patients with chronic noncancer pain.

Drug treatments for pruritus in adult palliative care

BACKGROUND

Pruritus is a rare but troublesome symptom in palliative-care patients with a variety of underlying diseases. The pharmacotherapy of pruritus is often off-label, and an evidence-based evaluation is needed.

METHODS

A Cochrane Review published in 2013 was updated with a systematic literature search up to January 2014. Randomized and controlled trials (RCTs) with adult palliative-care patients were included.

RESULTS

In the 43 RCTs that were analyzed, three of which were more recent than the Cochrane Review, 8 clinically relevant active substances were investigated in a total of 19 RCTs. Effective drugs for pruritus in palliative-care patients included paroxetine for pruritus of diverse origins (1 RCT; strong effect) and indomethacin for HIV-induced prutitus (1 RCT; median effect = moderate reduction). Effective drugs for pruritus in uremia were gabapentin (2 RCTs; strong effect), nalfurafin (3 RCTs; moderate effect), naltrexone (3 RCTs; heterogeneous effects, ranging from weak to strong), and cromoglicic acid (2 RCTs; moderate to strong effect). Effective drugs for cholestatic pruritus were rifampicin (3 RCTs; moderate effect), flumecinol (2 RCTs; weak to moderate effect), and naltrexone (2 RCTs; moderate to strong effect). Undesired effects were most common with naltrexone (dizziness: 0% -50% , nausea: 0% -50% ) and nalfurafin (nasopharyngitis: 8% -12% , insomnia: 7% -15%).

CONCLUSION

In view of the diverse etiologies of pruritus in palliative-care patients, careful consideration should be given to the choice of drug used to treat it. The substances listed here have moderate to strong antipruritic effects and merit further study in RCTs of high methodological quality.

Quality of life and healthcare resource in patients receiving opioids for chronic pain: a review of the place of oxycodone/naloxone

In patients managed with opioids for chronic pain, opioid-induced bowel dysfunction—specifically, opioid-induced constipation (OIC)—is a common side effect, which has a significant impact on quality of life (QoL). The most recent developments for management of OIC are opioid antagonists, including naloxone, a competitive antagonist of peripheral opioid receptors that reverses opioid-induced peripheral gastrointestinal (GI) effects. A prolonged-release formulation of naloxone is available in combination with oxycodone (OXN PR). To review the specific role of OXN PR in the management of chronic pain and OIC and its impact on QoL and healthcare costs, a review of available relevant literature was conducted. Healthcare costs can be up to ten times higher for patients with GI events than for those without. Assessment of QoL in patients with OIC is essential, and multiple tools for its evaluation are available. The Bowel Function Index (BFI), a tool that was specifically developed and validated to measure bowel function in patients with OIC, can be an indication of QoL. In patients with moderate-to-severe chronic pain, randomized trials have demonstrated that OXN PR has equal analgesic efficacy and safety, but results in improved bowel function, compared with prolonged-release oxycodone (Oxy PR) alone. In conclusion, randomized studies using the BFI, as well as real-world clinical practice observations, have demonstrated improved QoL for patients taking OXN PR. This combination should allow more patients to benefit from the analgesic efficacy of opioid therapy and should minimize the side effects of constipation that correspond to improvements in QoL and healthcare offsets.

Developments in managing severe chronic pain: role of oxycodone-naloxone extended release

Chronic pain is a highly disabling condition, which can significantly reduce patients’ quality of life. Prevalence of moderate and severe chronic pain is high in the general population, and it increases significantly in patients with advanced cancer and older than 65 years. Guidelines for the management of chronic pain recommend opioids for the treatment of moderate-to-severe pain in patients whose pain is not responsive to initial therapies with paracetamol and/or nonsteroidal anti-inflammatory drugs. Despite their analgesic efficacy being well recognized, adverse events can affect daily functioning and patient quality of life. Opioid-induced constipation (OIC) occurs in 40% of opioid-treated patients. Laxatives are the most common drugs used to prevent and treat OIC. Laxatives do not address the underlying mechanisms of OIC; for this reason, they are not really effective in OIC treatment. Naloxone is an opioid receptor antagonist with low systemic bioavailability. When administered orally, naloxone antagonizes the opioid receptors in the gut wall, while its extensive first-pass hepatic metabolism ensures the lack of antagonist influence on the central-mediated analgesic effect of the opioids. A prolonged-release formulation consisting of oxycodone and naloxone in a 2:1 ratio was developed trying to reduce the incidence of OIC maintaining the analgesic effect compared with use of the sole oxycodone. This review includes evidence related to use of oxycodone and naloxone in the long-term management of chronic non-cancer pain and OIC.

Fixed-Dose Subcutaneous Methylnaltrexone in Patients with Advanced Illness and Opioid-Induced Constipation: Results of a Randomized, Placebo-Controlled Study and Open-Label Extension

Background: Subcutaneous methylnaltrexone (MNTX), dosed based on body weight, is efficacious and well tolerated in inducing bowel movements in patients with advanced illness and opioid-induced constipation (OIC); however, fixed-dose administration of MNTX may improve ease of administration.

Objective: The study objective was to assess safety and efficacy of fixed-dose MNTX in two phase 4 trials.

Methods: In a double-blind, randomized, placebo-controlled trial (RCT), patients with advanced illness and OIC received MNTX (8 mg or 12 mg by body weight [38 kg to <62 kg or ≥62 kg, respectively]) or placebo every other day (QOD) for two weeks. Patients completing the RCT could enroll in an open-label extension (OLE) study with MNTX administered as needed (PRN). The primary endpoint was percentage of patients with a rescue-free bowel movement (RFBM) within four hours after ≥2 of the first 4 doses in the first week.

Results: In the RCT, 116 and 114 patients received MNTX and placebo, respectively, and 149 patients continued to the OLE study. The percentage of patients achieving primary endpoint was 62.9% and 9.6% for MNTX and placebo groups, respectively (p<0.0001). Median time to RFBM after the first dose was 0.8 hour and 23.6 hours in MNTX and placebo groups, respectively (p<0.0001). Efficacy results during the OLE study were consistent with the RCT. MNTX demonstrated a favorable safety profile in the RCT and OLE study.

Conclusion: Fixed-dose MNTX administered QOD in the RCT and PRN in the OLE study demonstrated robust efficacy and was well tolerated in treating OIC in patients with advanced illness.

Emerging therapies for patients with symptoms of opioid-induced bowel dysfunction

Opioid-induced bowel dysfunction (OIBD) comprises gastrointestinal (GI) symptoms, including dry mouth, nausea, vomiting, gastric stasis, bloating, abdominal pain, and opioid-induced constipation, which significantly impair patients’ quality of life and may lead to undertreatment of pain. Traditional laxatives are often prescribed for OIBD symptoms, although they display limited efficacy and exert adverse effects. Other strategies include prokinetics and change of opioids or their administration route. However, these approaches do not address underlying causes of OIBD associated with opioid effects on mostly peripheral opioid receptors located in the GI tract. Targeted management of OIBD comprises purely peripherally acting opioid receptor antagonists and a combination of opioid receptor agonist and antagonist. Methylnaltrexone induces laxation in 50%–60% of patients with advanced diseases and OIBD who do not respond to traditional oral laxatives without inducing opioid withdrawal symptoms with similar response (45%–50%) after an oral administration of naloxegol. A combination of prolonged-release oxycodone with prolonged-release naloxone (OXN) in one tablet (a ratio of 2:1) provides analgesia with limited negative effect on the bowel function, as oxycodone displays high oral bioavailability and naloxone demonstrates local antagonist effect on opioid receptors in the GI tract and is totally inactivated in the liver. OXN in daily doses of up to 80 mg/40 mg provides equally effective analgesia with improved bowel function compared to oxycodone administered alone in patients with chronic non-malignant and cancer-related pain. OIBD is a common complication of long-term opioid therapy and may lead to quality of life deterioration and undertreatment of pain. Thus, a complex assessment and management that addresses underlying causes and patomechanisms of OIBD is recommended. Newer strategies comprise methylnaltrexone or OXN administration in the management of OIBD, and OXN may be also considered as a preventive measure of OIBD development in patients who require opioid administration.

Methylnaltrexone: its pharmacological effects alone and effects on morphine in healthy volunteers

RATIONALE

Methylnaltrexone bromide (MTNX) is a peripherally acting mu-opioid receptor antagonist, prescribed for the treatment of opioid-induced constipation in patients with advanced illness who are receiving palliative care. Studies have used this drug to determine if other opioid-induced effects besides constipation are altered by MTNX in humans and have suggested, based on their results, that these other effects are altered by peripheral opioid actions.

OBJECTIVE

The primary objective of this report is to present results that provide indirect evidence that MTNX has centrally mediated effects, albeit slight, and secondarily to describe the effects of MTNX on psychopharmacological effects of morphine.

METHODS

In a crossover, randomized, placebo-controlled, double-blind study, 29 healthy volunteers received 0.45 mg/kg MTNX or saline subcutaneously, followed by saline intravenously. In three other conditions, 0.143 mg/kg of morphine sulfate administered intravenously was preceded by subcutaneous administration of 0, 0.225, or 0.45 mg/kg MTNX. Before and after drug administration, subjective and physiological measures, including pupil diameter, were assessed.

RESULTS

Two separate analyses confirmed that 0.45 mg/kg MTNX alone induced a slight degree of miosis, a centrally mediated opioid agonist effect. This dose had minimal subjective effects. MTNX at either or both the 0.225 and 0.45 mg/kg dose reduced some subjective effects of morphine without altering miosis.

CONCLUSIONS

We present indirect evidence that MTNX crosses the blood-brain barrier in humans. Therefore, whether the reductions in subjective effects of morphine by MTNX that were observed in past studies and in this study can be attributed to peripheral mechanisms is open to question.

Advances in pharmacotherapy for opioid-induced constipation - a systematic review

INTRODUCTION

Opioid-induced constipation (OIC) is one of the most frequent and burdening adverse events (AE) of opioid therapy. This systematic review aimed to evaluate efficacy and safety of drugs in randomized controlled trials (RCTs) with adult OIC patients.

AREAS COVERED

Efficacy assessment focused on objective outcome measures (OOMs): bowel movement (BM) frequency, BM within 4 h and time to first BM. Twenty-one studies examining seven drugs were identified. Methylnaltrexone showed improvements in all three OOMs. RCTs in naloxone and alvimopan tended to be effective for BM frequency measures. Naloxegol (≥ 12.5 mg) improved all OOMs. Though effectiveness of lubiprostone was demonstrated for all OOMs, group differences were small to moderate. CB-5945 and prucalopride tended to increase BM frequency, especially for 0.1 mg twice daily and 4 mg daily, respectively. Besides nausea and diarrhea, abdominal pain was the most frequent AE for all drugs (risk ratio, range: 1.52 - 5.06) except for alvimopan. Treatment-related serious AEs were slightly higher for alvimopan (cardiac events) and prucalopride (severe abdominal pain, headache). Pain scores for placebo and intervention groups were similar for all drugs.

EXPERT OPINION

Finding a consensus definition and inclusion criteria for OIC plus a rational balance between efficacy and AEs of drugs remain future challenges.

Neurochemical phenotype and function of endomorphin 2-immunopositive neurons in the myenteric plexus of the rat colon

The distribution and activity of endomorphins (EMs), which are endogenous μ-opioid receptor (MOR) ligands in the gastrointestinal tract (GI), are yet to be elucidated. The current study aimed to shed light on this topic. EM2 was expressed in the enteric neurons in the myenteric plexus of the mid-colon. Of the EM2-immunoreactive (EM2-IR) neurons, 53 ± 4.6%, 26 ± 4.5%, 26 ± 2.8% and 49 ± 4.2% displayed immunopositive staining for choline acetyl transferase (ChAT), substance P (SP), vasoactive intestinal peptide (VIP) and nitric oxide synthetase (NOS), respectively. A bath application of EM2 (2 μM) enhanced spontaneous contractile amplitude and tension, which were reversed by β-FNA (an antagonist of MOR) but not NG-nitro-L-arginine methyl ether (L-NAME, a non-selective inhibitor of NOS) or VIP6-28 (an antagonist of the VIP receptor) in the colonic strips. EM2 significantly suppressed inhibitory junction potentials (IJPs) in 14 of the 17 examined circular muscle cells, and this effect was not antagonized by preincubation in L-NAME. EM2 was widely expressed in interneurons and motor neurons in the myenteric plexus and presynaptically inhibited fast IJPs, thereby enhancing spontaneous contraction and tension in the colonic smooth muscle.

Natural product and natural product derived drugs in clinical trials

The 25 Natural Product (NP)-derived drugs launched since 2008 and the 100 NP-derived compounds and 33 Antibody Drug Conjugates (ADCs) in clinical trials or in registration at the end of 2013 are reviewed.

The place of oxycodone/naloxone in chronic pain management

Opioid analgesics are usually effective in the management of severe chronic pain. However, symptoms of opioid-induced bowel dysfunction (OIBD) are common during opioid therapy. Opioid-induced bowel dysfunction is often unsuccessfully managed due to limited effectiveness and numerous adverse effects of traditional laxatives. Newer treatment possibilities directed at the pathomechanism of OIBD comprise combined prolonged-release oxycodone with prolonged-release naloxone (oxycodone/naloxone) tablets. Oxycodone/naloxone provides effective analgesia with limited impact on bowel function as oxycodone displays high oral bioavailability and naloxone act as local antagonist on opioid receptors in the gastrointestinal tract due to nearly complete inactivation in the liver. Oxycodone/naloxone is administered to opioid-naive patients with severe pain and those unsuccessfully treated with weak opioids. Oxycodone/naloxone may be also administered to patients treated with strong opioids who experience intense symptoms of OIBD. Studies conducted to date indicate that oxycodone/naloxone is an important drug in chronic pain management, prevention and treatment of OIBD.