Development of peripheral opioid antagonists' new insights into opioid effects

No Effect of Methylnaltrexone on Acute Pancreatitis Severity: A Multicenter Randomized Controlled Trial

INTRODUCTION

Opioids used to manage severe pain in acute pancreatitis (AP) might exacerbate the disease through effects on gastrointestinal and immune functions. Methylnaltrexone, a peripherally acting µ-opioid receptor antagonist, may counteract these effects without changing analgesia.

METHODS

This double-blind, randomized, placebo-controlled trial included adult patients with AP and systemic inflammatory response syndrome at 4 Danish centers. Patients were randomized to receive 5 days of continuous intravenous methylnaltrexone (0.15 mg/kg/d) or placebo added to the standard of care. The primary end point was the Pancreatitis Activity Scoring System score after 48 hours of treatment. Main secondary outcomes included pain scores, opioid use, disease severity, and mortality.

RESULTS

In total, 105 patients (54% men) were randomized to methylnaltrexone (n = 51) or placebo (n = 54). After 48 hours, the Pancreatitis Activity Scoring System score was 134.3 points in the methylnaltrexone group and 130.5 points in the placebo group (difference 3.8, 95% confidence interval [CI] -40.1 to 47.6; P = 0.87). At 48 hours, we found no differences between the groups in pain severity (0.0, 95% CI -0.8 to 0.9; P = 0.94), pain interference (-0.3, 95% CI -1.4 to 0.8; P = 0.55), and morphine equivalent doses (6.5 mg, 95% CI -2.1 to 15.2; P = 0.14). Methylnaltrexone also did not affect the risk of severe disease (8%, 95% CI -11 to 28; P = 0.38) and mortality (6%, 95% CI -1 to 12; P = 0.11). The medication was well tolerated.

DISCUSSION

Methylnaltrexone treatment did not achieve superiority over placebo for reducing the severity of AP.

Successful Use of Intravenous Methylnaltrexone for Opioid-Induced Constipation in Critically Ill Pediatric Patients

Objectives  Methylnaltrexone is U.S. Food and Drug Administration (FDA) approved as a subcutaneous injection for adults with opioid-induced constipation (OIC). Case series have described the use of methylnaltrexone for OIC in the pediatric oncology population. There are limited data describing its intravenous use in critically ill pediatric patients. Methods  We conducted a retrospective observational study at St. Louis Children's Hospital. Patients less than 18 years old who received at least one dose of intravenous methylnaltrexone while admitted to an intensive care unit between January 2016 and August 2019 were included. The primary outcome was documented laxation within 24 hours of methylnaltrexone administration. Results  Sixteen patients received a total of 34 doses of intravenous methylnaltrexone. Patients received a median of 1.69 (interquartile range [IQR], 0.9-4.86) morphine milligram equivalents per kilogram per 24 hours, over a median of 14 days (IQR, 11-30), before methylnaltrexone administration. The median dose of methylnaltrexone was 0.15 mg/kg (IQR, 0.15-0.16). Ten patients (63%) responded to the first dose of methylnaltrexone, and 14 patients (88%) responded to at least one dose. Overall, 26 doses (76%) led to patient response. Four patients (25%) experienced adverse events (emesis, abdominal pain) after methylnaltrexone administration. No signs or symptoms of opioid withdrawal were documented. Conclusions  Intravenous methylnaltrexone appears to be safe and effective in treating OIC in critically ill pediatric patients. No serious adverse events or signs of opioid withdrawal were observed after single and repeat dosing. Patients responded to methylnaltrexone with varying opioid dosing and durations prior to administration.

Influence of exogenous opioids on the acute inflammatory response in the perioperative period of oncological surgery: a clinical study

BACKGROUND

Recently, opioids have been related to trigger changes in cytokine release and tumor angiogenesis processes, influencing tumor growth, metastasis, and recurrence.

METHODS

This is a prospective randomized clinical study to test whether if exogenous opioids used in the anesthesia during cancer surgery can affect the systemic inflammatory and immunological patterns. Patients were randomly allocated to the OP (opioid...inclusive) or OF (opioid-free) anesthesia group. A total of 45 patients were selected, being carriers of prostate, stomach, pancreas, bile ducts, breast, colon, lung, uterus, kidneys, or retroperitoneum tumors. Plasma levels of IL-4, IL-12, IL-17A, and TNF-.., and their oxidative stress profile before and after surgery were evaluated in both groups. In vitro tests were performed by using healthy donor blood incubated with each isolated drug used in patients... anesthesia for 1...hour, the same cytokines were measured in plasma.

RESULTS

There was a significant reduction in lipid peroxidation in both groups. Patients from OF group had a significant consumption of IL-12 in the perioperative period. The other cytokines evaluated did not vary. It was also observed a significant correlation between IL-12 and TNF-.. levels in the OF-post group. Except for atracurium, all tested drugs led to a reduction in IL-12 levels.

CONCLUSIONS

This study demonstrated that there is a reduction of IL-12 in the OF-post patients, suggesting acute consumption and that this seems to be a general mechanism of anesthetic drugs, as demonstrated in vitro. Also, these findings bring us to reflect if IL-12 changes may influence the disease progression and recurrence.

Peripherally restricted transthyretin-based delivery system for probes and therapeutics avoiding opioid-related side effects

Several investigations into the sites of action of opioid analgesics have utilized peripherally acting mu-opioid receptor antagonists (PAMORAs), which have been incorrectly assumed to possess limited permeability across the blood-brain barrier. Unfortunately, the poor pharmacokinetic properties of current PAMORAs have resulted in misunderstandings of the role of central nervous system and gastrointestinal tract in precipitating side effects such as opioid-induced constipation. Here, we develop a drug delivery approach for restricting the passage of small molecules across the blood-brain barrier. This allows us to develop naloxone- and oxycodone-based conjugates that display superior potency, peripheral selectivity, pharmacokinetics, and efficacy in rats compared to other clinically used PAMORAs. These probes allow us to demonstrate that the mu-opioid receptors in the central nervous system have a fundamental role in precipitating opioid-induced constipation. Therefore, our conjugates have immediate use as pharmacological probes and potential therapeutic agents for treating constipation and other opioid-related side effects.

Antagonists of the Mu-Opioid Receptor in the Cancer Patient: Fact or Fiction?

Purpose of Review

Antagonists of mu-opioid receptor role in cancer progression remains to be elucidated. The objective of this review was to summarize the available evidence on antagonists of mu-opioid receptor effect on tumor progression and prognosis in different types of cancers and an evaluation of the available findings on their mechanism of action.

Recent Findings

We have found studies related to methylnaltrexone (MNTX) and naltrexone (NTX) usage in cancer outcomes-related setting. We found consistent preclinical evidence of a potential action of MNTX and NTX on cancer growth and spread mediated mainly by effect on the opioid growth factor receptor (OGFr) axis, which results in depressed cell replication. However, clinical results are scarce and limited to poor-quality evidence.

Summary

Further high-quality studies are warranted to study antagonists of mu-opioid receptor role as a therapeutic option in different types of cancer, especially in patients where the classical treatment causes unacceptable side effects.

Opioids Cause Sex-Specific Vascular Changes via Cofilin-Extracellular Signal-Regulated Kinase Signaling: Female Mice Present Higher Risk of Developing Morphine-Induced Vascular Dysfunction than Male Mice

Recent studies have shown that chronic use of prescription or illicit opioids leads to an increased risk of cardiovascular events and pulmonary arterial hypertension. Indices of vascular age and arterial stiffness are also shown to be increased in opioid-dependent patients, with the effects being more marked in women. There are currently no studies investigating sex-specific vascular dysfunction in opioid use, and the mechanisms leading to opioid-induced vascular damage remain unknown. We hypothesized that exposure to exogenous opioids causes sex-specific vascular remodeling that will be more pronounced in female. Acknowledging the emerging roles of cofilins and extracellular signal-regulated kinases (ERKs) in mediating actin dynamics, we investigated the effects of morphine on these molecules. Twenty-four hour exposure to morphine increased inactivated cofilin and activated ERKs in resistance arteries from female mice, which may promote stress fiber over-assembly. We also performed continuous intraluminal infusion of morphine in pressurized resistance arteries from male and female mice using culture pressure myographs. We observed that morphine reduced the vascular diameter in resistance arteries from female, but not male mice. These results have significant implications for the previously unexplored role of exogenous opioids as a modifiable cardiovascular risk factor, especially in women.

Pain in sickle cell disease: current and potential translational therapies

Pain is a major comorbidity of sickle cell disease (SCD). Patients with SCD may suffer from both acute and chronic pain. Acute pain is caused by recurrent and unpredictable episodes of vaso-occlusive crises (VOC), whereas the exact etiology of chronic pain is still unknown. Opioids are the mainstay for pain treatment, but the opioid epidemic has significantly altered access to prescription opioids and has brought concerns over their long-term use into the forefront, which have negatively impacted the treatment of sickle pain. Opioids remain potent analgesics but growing opioid-phobia has led to the realization of an unmet need to develop nonopioid therapies that can provide relief for severe sickle pain. This realization has contributed to the approval of 3 different drugs by the Food and Drug Administration (FDA) for the treatment of SCD, particularly to reduce VOC and/or have an impact on the pathobiology of SCD. In this review, we outline the challenges and need for validation of side-effects of opioids and provide an update on the development of mechanism-based translational therapies, specifically targeting pain in SCD.

Precision Lactobacillus reuteri therapy attenuates luminal distension-associated visceral hypersensitivity by inducing peripheral opioid receptors in the colon

Luminal distension and abdominal pain are major clinical hallmarks of obstructive bowel disorders and functional bowel disorders linked to gut dysbiosis. Our recent studies found that chronic lumen distension increased visceral sensitivity and decreased abundance of gut commensal Lactobacillus reuteri in a rodent model of partial colon obstruction (OB). To establish causation, we performed precision microbial therapy to assess whether recolonization of L. reuteri prevents visceral hypersensitivity in lumen distension, and if so, to identify the gut-microbiota mechanism. Lumen distension was induced in Sprague-Dawley rats by implanting an OB band in the distal colon for up to 7 days. L. reuteri strains or vehicle were gavage ingested 1 × 10 colony-forming units/g daily starting 2 days before OB. L. reuteri rat strains that were able to recolonize obstructed colon significantly improved food intake and body weight in OB rats, and attenuated referred visceral hyperalgesia measured by the withdrawal response to von Frey filament applications to the abdomen. Mechanistically, L. reuteri treatment attenuated hyperexcitability of the dorsal root ganglia neurons projecting to the distended colon by promoting opioid receptor function in affected tissues. The expression of µ, δ, and κ opioid receptors was significantly downregulated in colonic muscularis externae and sensory neurons in OB rats. However, L. reuteri treatment prevented the loss of opioid receptors. Furthermore, administration of peripheral opioid receptor antagonist naloxone methiodide abolished the analgesic effect of L. reuteri in OB. In conclusion, precision L. reuteri therapy prevents lumen distension-associated visceral hypersensitivity by local bacterial induction of opioid receptors.

Blood-brain barrier: mechanisms governing permeability and interaction with peripherally acting μ-opioid receptor antagonists

The blood-brain barrier (BBB) describes the unique properties of endothelial cells (ECs) that line the central nervous system (CNS) microvasculature. The BBB supports CNS homeostasis via EC-associated transport of ions, nutrients, proteins and waste products between the brain and blood. These transport mechanisms also serve as physiological barriers to pathogens, toxins and xenobiotics to prevent them from contacting neural tissue. The mechanisms that govern BBB permeability pose a challenge to drug design for CNS disorders, including pain, but can be exploited to limit the effects of a drug to the periphery, as in the design of the peripherally acting μ-opioid receptor antagonists (PAMORAs) used to treat opioid-induced constipation. Here, we describe BBB physiology, drug properties that affect BBB penetrance and how data from randomized clinical trials of PAMORAs improve our understanding of BBB permeability.

Naldemedine: Peripherally Acting Opioid Receptor Antagonist for Treating Opioid-induced Adverse Effects

Opioids are widely used for pain management in moderate-to-severe pain. However, opioids are associated with adverse events, such as constipation and emesis/vomiting. To reduce these undesired effects, a structure-activity relationship study of morphinan derivatives was conducted, and a promising lead compound with inhibitory effects on opioid receptors was obtained. Further improvement in the potency and pharmacokinetic profiles of the lead compound led to the discovery of naldemedine, which showed anti-constipation and anti-emetic effects against these adverse events that were induced by morphine without influencing morphine's analgesic effect. Naldemedine was launched in Japan and the USA in 2017 and in the EU in 2019, for treating opioid-induced constipation.

Exogenous morphine inhibits the growth of human gastric tumor in vivo

Morphine is commonly used to relieve severe pain that is often associated with cancer. Previous studies have found that morphine could affect cancer development; however, this effect is poorly understood. To further clarify the anti-cancer potential of morphine for the development of cancer in vivo, we observed how morphine affects the growth of human gastric tumor in a murine xenografting model and the expression of NF-κB and its downstream target genes (Bcl-2/Bax, cyclind1, and VEGF). The growth of the tumor was evaluated by its growth curves. The mRNA expression levels of NF-κB, Bcl-2/Bax, cyclind1, and VEGF were assessed by semi-quantitative polymerase chain reaction (qPCR). The protein expression of NF-κB, Bcl-2/Bax, cyclind1, and VEGF was detected by immunochemistry staining and western blot. Our data showed that morphine effectively inhibited the tumor growth in the nude mice. Morphine inhibits the expression of NF-κB, Bcl-2, cyclind1, and VEGF while enhancing the expression of Bax in the tumors. Furthermore, the anti-cancer effects of morphine could be reversed by naloxone. The mechanism might be associated with the action of opioid receptors that downregulate the expression of NF-κB leading to the regulation of the downstream target genes (Bcl-2/Bax, cylind1, and VEGF) in the tumors.

Methylnaltrexone for the treatment of opioid-induced constipation and gastrointestinal stasis in intensive care patients. Results from the MOTION trial

Purpose

Constipation can be a significant problem in critically unwell patients, associated with detrimental outcomes. Opioids are thought to contribute to the mechanism of bowel dysfunction. We tested if methylnaltrexone, a pure peripheral mu-opioid receptor antagonist, could reverse opioid-induced constipation.

Methods

The MOTION trial is a multi-centre, double blind, randomised placebo-controlled trial to investigate whether methylnaltrexone alleviates opioid-induced constipation (OIC) in critical care patients. Eligibility criteria included adult ICU patients who were mechanically ventilated, receiving opioids and were constipated (had not opened bowels for a minimum 48 h) despite prior administration of regular laxatives as per local bowel management protocol. The primary outcome was time to significant rescue-free laxation. Secondary outcomes included gastric residual volume, tolerance of enteral feeds, requirement for rescue laxatives, requirement for prokinetics, average number of bowel movements per day, escalation of opioid dose due to antagonism/reversal of analgesia, incidence of ventilator-associated pneumonia, incidence of diarrhoea and Clostridium difficile infection and finally 28 day, ICU and hospital mortality.

Results

A total of 84 patients were enrolled and randomized (41 to methylnaltrexone and 43 to placebo). The baseline demographic characteristics of the two groups were generally well balanced. There was no significant difference in time to rescue-free laxation between the groups (Hazard ratio 1.42, 95% CI 0.82–2.46, p = 0.22). There were no significant differences in the majority of secondary outcomes, particularly days 1–3. However, during days 4–28, there were fewer median number of bowel movements per day in the methylnaltrexone group, (p = 0.01) and a greater incidence of diarrhoea in the placebo group (p = 0.02). There was a marked difference in mortality between the groups, with ten deaths in the methylnaltrexone group and two in the placebo group during days 4–28 (p = 0.007).

Conclusion

We found no evidence to support the addition of methylnaltrexone to regular laxatives for the treatment of opioid-induced constipation in critically ill patients; however, the confidence interval was wide and a clinically important difference cannot be excluded.

Electronic supplementary material

The online version of this article (10.1007/s00134-019-05913-6) contains supplementary material, which is available to authorized users.

Alternating Current Iontophoresis for Control of Postoperative Pain

Control of early postoperative pain entails the use of various medications including acetaminophen, nonsteroidal anti-inflammatory drugs, selective cyclooxygenase-2 inhibitors, tramadol, and opioids. However, these medications should be carefully administered in patients with aspirin-exacerbated respiratory disease because some medications may trigger adverse reactions after maxillofacial surgeries. The goal of postoperative pain control in patients with aspirin-exacerbated respiratory disease is to eliminate pain without complications. Local anesthesia is an efficient tool for the control of postoperative pain after maxillofacial surgeries. We utilized a transdermal drug delivery system, iontophoresis by alternating current, in order to develop an alternative technique for administering local anesthetic to control postoperative pain in 2 patients with aspirin-exacerbated respiratory disease. A visual analogue scale was used to objectively measure the severity of pain. A 55-year-old woman who underwent mandibular wisdom tooth extraction and an 18-year-old woman who underwent sagittal split ramus osteotomy of the mandible both complained of pain multiple times. After application of iontophoresis, the visual analogue scale score was reduced to zero and postoperative pain could be controlled. There were no adverse events such as bronchospasm or skin irritation after the application of iontophoresis by alternating current.

Design, synthesis and evaluation of 111In labeled DOTA-conjugated tetrapeptides having high affinity and selectivity for mu opioid receptors

INTRODUCTION

Peripheral mu (μ) opioid receptors are implicated in pain, bowel dysfunction and the progression of certain cancers. In an effort to identify radioligands well suited for imaging these peripheral sites, we have prepared and evaluated four hydrophilic ¹¹¹In labeled DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) conjugated μ tetrapeptides.

METHODS

Peptides were prepared by solid-phase techniques, using orthogonal strategies to achieve branching to DOTA, and then characterized by HPLC, mass spectroscopy and amino acid analysis. Scaffolds included novel peptide H-Dmt-D-Ala-Phe-Orn-NH₂ (DAPO), where Dmt = 2',6'-dimethyltyrosine, and known peptide H-Dmt-D-Arg-Phe-Lys-NH₂ ([Dmt¹]DALDA). Constructs had DOTA conjugation at the Orn⁴ or Lys⁴ side chains, or to the C-terminal through a hexanoic acid-lysine linker. Indium(III) complexation and ¹¹¹In radiolabeling were accomplished by standard methods. Protein binding and Log D_7.4 were determined. Binding and pharmacological profiles were obtained in vitro. Biodistribution and radiometabolite studies were conducted using male CD-1 mice.

RESULTS

All four indium(III)-DOTA conjugates derived from DAPO and [Dmt¹]DALDA showed good selectivity and subnanomolar affinity for μ opioid receptors. One radioligand, H-Dmt-D-Ala-Phe-Orn(δ-[¹¹¹In]In-DOTA)-NH₂, showed 25% specific binding in vivo to μ sites in mouse gut. Notably, this was the least polar of the series, and also showed low sensitivity to modulation of binding by sodium ions. All radioligands showed high kidney uptake of radiometabolites.

CONCLUSIONS

Visualizing peripheral μ opioid receptors using ¹¹¹In labeled DOTA-conjugated tetrapeptides appears feasible, but structural modifications to enhance specific binding and metabolic stability, as well as to reduce kidney uptake, will be required.

ADVANCES IN KNOWLEDGE

This study shows in vivo labeling of peripheral μ opioid receptors by a tetrapeptide radioligand, and provides information that should prove useful in the design of peptide radioligands having optimal properties.

Complete blood count alterations due to the opioid use: what about the lymphocyte-related ratios, especially in monocyte to lymphocyte ratio and platelet to lymphocyte ratio?

This study was designed to compare the complete blood count values of opioid users (N = 61) and healthy subjects (N = 61), particularly monocyte-to-lymphocyte ratio (MLR) and platelet-to-lymphocyte ratio (PLR). PLR, MLR, and percentage of monocyte (MONO%) were significantly lower in opioid use disorder (OUD) group (P = 0.012, P = 0.005, P = 0.000). The area under the ROC curve of MLR and PLR levels for OUD was 0.349 and 0.368. MONO% correlated with substance use duration. Measurements like lymphocyte-related ratios and MONO% in opioid use can be important in substance monitoring, detection, and differentiation of acute and chronic conditions.

In Search of the Ideal Promotility Agent: Optimal Use of Currently Available Promotility Agents for Nutrition Therapy of the Critically Ill Patient

PURPOSE OF REVIEW

Enteral nutrition therapy is essential in the management of critically ill patients. Prokinetic agents have been used successfully to aid in the delivery of nutrition and improve feeding tolerance in patients in the intensive care unit (ICU). The aim of this report is to review the existing promotility agents available for use in the critically ill as well as outline the role of potential investigative drugs in order to provide a guide to the management of this difficult and important clinical dilemma.

RECENT FINDINGS

While no single currently available agent currently meets all of the desired goals in the critical care setting, there are an increasing number of available agents from which to choose including motilin receptor agonists, 5HT4 receptor agonists, D2 receptor antagonists, and Mu opioid receptor antagonists. We recommend a multifaceted approach to optimizing enteral nutrition in the critical care setting which should include the early, prophylactic use of promotility agents and should focus on the management of reversible causes of impaired gastrointestinal motility.

Opioid-Induced Constipation and Bowel Dysfunction: A Clinical Guideline

OBJECTIVE

To formulate timely evidence-based guidelines for the management of opioid-induced bowel dysfunction.

SETTING

Constipation is a major untoward effect of opioids. Increasing prescription of opioids has correlated to increased incidence of opioid-induced constipation. However, the inhibitory effects of opioids are not confined to the colon, but also affect higher segments of the gastrointestinal tract, leading to the coining of the term "opioid-induced bowel dysfunction."

METHODS

A literature search was conducted using Medline, EMBASE, and EMBASE Classic, and the Cochrane Central Register of Controlled Trials. Predefined search terms and inclusion/exclusion criteria were used to identify and categorize relevant papers. A series of statements were formulated and justified by a comment, then labeled with the degree of agreement and their level of evidence as judged by the Strength of Recommendation Taxonomy (SORT) system.

RESULTS

From a list of 10,832 potentially relevant studies, 33 citations were identified for review. Screening the reference lists of the pertinent papers identified additional publications. Current definitions, prevalence, and mechanism of opioid-induced bowel dysfunction were reviewed, and a treatment algorithm and statements regarding patient management were developed to provide guidance on clinical best practice in the management of patients with opioid-induced constipation and opioid-induced bowel dysfunction.

CONCLUSIONS

In recent years, more insight has been gained in the pathophysiology of this "entity"; new treatment approaches have been developed, but guidelines on clinical best practice are still lacking. Current knowledge is insufficient regarding management of the opioid side effects on the upper gastrointestinal tract, but recommendations can be derived from what we know at present.

Treatment with methylnaltrexone is associated with increased survival in patients with advanced cancer

BACKGROUND

Methylnaltrexone (MNTX), a peripherally acting μ-opioid receptor (MOR) antagonist, is FDA-approved for treatment of opioid-induced constipation (OIC). Preclinical data suggest that MOR activation can play a role in cancer progression and can be a target for anticancer therapy.

PATIENTS AND METHODS

Pooled data from advanced end-stage cancer patients with OIC, despite laxatives, treated in two randomized (phase III and IV), placebo-controlled trials with MNTX were analyzed for overall survival (OS) in an unplanned post hoc analysis. MNTX or placebo was given subcutaneously during the double-blinded phase, which was followed by the open-label phase, allowing MNTX treatment irrespective of initial randomization.

RESULTS

In two randomized, controlled trials, 229 cancer patients were randomized to MNTX (117, 51%) or placebo (112, 49%). Distribution of patients' characteristics and major tumor types did not significantly differ between arms. Treatment with MNTX compared with placebo [76 days, 95% confidence interval (CI) 43-109 versus 56 days, 95% CI 43-69; P = 0.033] and response (laxation) to treatment compared with no response (118 days, 95% CI 59-177 versus 55 days, 95% CI 40-70; P < 0.001) had a longer median OS, despite 56 (50%) of 112 patients ultimately crossing over from placebo to MNTX. Multivariable analysis demonstrated that response to therapy [hazard ratio (HR) 0.47, 95% CI 0.29-0.76; P = 0.002) and albumin ≥3.5 (HR 0.46, 95% CI 0.30-0.69; P < 0.001) were independent prognostic factors for increased OS. Of interest, there was no difference in OS between MNTX and placebo in 134 patients with advanced illness other than cancer treated in these randomized studies (P = 0.88).

CONCLUSION

This unplanned post hoc analysis of two randomized trials demonstrates that treatment with MNTX and, even more so, response to MNTX are associated with increased OS, which supports the preclinical hypothesis that MOR can play a role in cancer progression. Targeting MOR with MNTX warrants further investigation in cancer therapy.

CLINICAL TRIALS NUMBER

NCT00401362, NCT00672477.

Protocol for a randomised control trial of methylnaltrexone for the treatment of opioid-induced constipation and gastrointestinal stasis in intensive care patients (MOTION)

INTRODUCTION

Gastrointestinal dysmotility and constipation are common problems in intensive care patients. The majority of critical care patients are sedated with opioids to facilitate tolerance of endotracheal tubes and mechanical ventilation, which inhibit gastrointestinal motility and lead to adverse outcomes. Methylnaltrexone is a peripheral opioid antagonist that does not cross the blood-brain barrier and can reverse the peripheral side effects of opioids without affecting the desired central properties. This trial will investigate whether methylnaltrexone can reverse opioid-induced constipation and gastrointestinal dysmotility.

METHODS

This is a single-centre, multisite, double-blind, randomised, placebo-controlled trial. 84 patients will be recruited from 4 intensive care units (ICUs) within Imperial College Healthcare NHS Trust. Patients will receive intravenous methylnaltrexone or placebo on a daily basis if they are receiving opioid infusion to facilitate mechanical ventilation and have not opened their bowels for 48 hours. All patients will receive standard laxatives as per the clinical ICU bowel protocol prior to randomisation. The primary outcome of the trial will be time to significant rescue-free laxation following randomisation. Secondary outcomes will include tolerance of enteral feed, gastric residual volumes, incidence of pneumonia, blood stream and Clostridium difficile infection, and any reversal of central opioid effects.

ETHICS AND DISSEMINATION

The trial protocol, the patient/legal representative information sheets and consent forms have been reviewed and approved by the Harrow Research Ethics Committee (REC Reference 14/LO/2004). An independent Trial Steering Committee and Data Monitoring Committee are in place, with patient representation. On completion, the trial results will be published in peer-reviewed journals and presented at national and international scientific meetings.

TRIAL REGISTRATION NUMBER

2014-004687-37; Pre-results.

A118G Polymorphism in μ-Opioid Receptor Gene and Interactions with Smoking and Drinking on Risk of Oesophageal Squamous Cell Carcinoma

AIM

To investigate the single nucleotide polymorphism (SNP) of A118G and its interaction with smoking and drinking on oesophageal squamous cell carcinoma (ESCC) risk.

METHODS

A total of 960 subjects (545 males and 415 females) with a mean age of 58.1 ± 13.4 years were selected, including 490 ESCC patients and 470 normal control subjects. A logistic regression model was used to examine the association between A118G and ESCC and its interaction with A118G and current smoking and drinking. The odds ratio (OR) and 95% confident interval (95%CI) were calculated.

RESULTS

The frequency for the A allele of A118G was significantly higher in ESCC cases, OR (95%CI) = 1.22 (1.08-1.59). Logistic regression analysis showed a significant association between the A allele in A118G and increased ESCC risk. The ESCC risk was significantly higher in carriers of the A allele of the A118G polymorphism than those with GG (AG + AA vs. GG, adjusted OR (95%CI) = 1.20 (1.05-1.53)). We found that current smokers with AG or AA of the A118G genotype have the highest ESCC risk compared with never smokers with a GG genotype; the OR (95%CI) was 2.57 (1.66-3.33). Current drinkers with AG or AA of the A118G genotype have the highest ESCC risk compared with not currently drinking subjects with the GG genotype, OR (95%CI) = 2.36 (1.47-3.25), after adjusting for covariates.

CONCLUSION

The A allele of A118G and ESCC and additional interaction between the A allele of A118G and smoking or drinking were associated with increased ESCC risk.

The mu opioid receptor: A new target for cancer therapy?

Mu opioids are among the most widely used drugs for patients with cancer with both acute and chronic pain as well as in the perioperative period. Several retrospective studies have suggested that opioid use might promote tumor progression and as a result negatively impact survival in patients with advanced cancer; however, in the absence of appropriate prospective validation, any changes in recommendations for opioid use are not warranted. In this review, the authors present preclinical and clinical data that support their hypothesis that the mu opioid receptor is a potential target for cancer therapy because of its plausible role in tumor progression. The authors also propose the hypothesis that peripheral opioid antagonists such as methylnaltrexone, which reverses the peripheral effects of mu opioids but maintains centrally mediated analgesia and is approved by the US Food and Drug Administration for the treatment of opioid-induced constipation, can be used to target the mu opioid receptor.

Methylnaltrexone for Opioid-Induced Constipation in Children and Adolescents and Young Adults with Progressive Incurable Cancer at the End of Life

BACKGROUND

Opioid-induced constipation (OIC) is common among children and adolescents and young adults (AYA) with progressive incurable cancer. Although methylnaltrexone is a successful treatment for OIC in adult cancer patients, no case series has established its safety and efficacy in pediatric cancer patients.

OBJECTIVES

The aim of the study was to describe the safety and efficacy of methylnaltrexone use for OIC in children and AYA with progressive incurable cancer at the end of life in the inpatient and outpatient settings.

METHODS

We conducted a retrospective review of medical records of children and AYA with progressive incurable cancer who received methylnaltrexone at our institution from May 2008 to June 2013. Pharmacy data were reviewed for each patient and a chart review was performed for documentation of laxation and side effects.

RESULTS

Of the 9 patients (age range: 17 months to 21 years) with progressive incurable cancer who developed OIC, 7 (78%) had laxation after methylnaltrexone administration (0.15 mg/kg/dose). Of these 7 patients, 5 (71%) had laxation with the first dose, and 5 (71%) who responded had a continued response to repeated doses. The longest a patient regularly received methylnaltrexone was 9 months. Of 5 patients with intraabdominal disease, 4 (80%) had laxation. There were no negative side effects in any of the patients. Also, there was no increase in pain either qualitatively or by pain score.

CONCLUSIONS

Methylnaltrexone appears to be safe and efficacious in treating OIC in children and AYA with progressive incurable cancer. Methylnaltrexone was tolerated in both the inpatient and outpatient settings and with repeated dosing.

Morphine for the treatment of pain in sickle cell disease

Pain is a hallmark of sickle cell disease (SCD) and its treatment remains challenging. Opioids are the major family of analgesics that are commonly used for treating severe pain. However, these are not always effective and are associated with the liabilities of their own. The pharmacology and multiorgan side effects of opioids are rapidly emerging areas of investigation, but there remains a scarcity of clinical studies. Due to opioid-induced endothelial-, mast cell-, renal mesangial-, and epithelial-cell-specific effects and proinflammatory as well as growth influencing signaling, it is likely that when used for analgesia, opioids may have organ specific pathological effects. Experimental and clinical studies, even though extremely few, suggest that opioids may exacerbate existent organ damage and also stimulate pathologies of their own. Because of the recurrent and/or chronic use of large doses of opioids in SCD, it is critical to evaluate the role and contribution of opioids in many complications of SCD. The aim of this review is to initiate inquiry to develop strategies that may prevent the inadvertent effect of opioids on organ function in SCD, should it occur, without compromising analgesia.

Efficacy of bilateral mental nerve block with bupivacaine for postoperative pain control in mandibular parasymphysis fractures

Background and aims. Postoperative pain control is extremely important for both patients and surgeons; in this context, long-acting local anesthesia can play an important role after open reduction of maxillofacial fractures. The purpose of this study was to evaluate the effect of bilateral mental nerve block with bupivacaine on postoperative pain control in mandibular symphyseal fractures.

Materials and methods. Fifty patients with pure mandibular symphyseal fractures were studied in two control and study groups. In contrast to the control group, the study group received bilateral mental nerve block with bupivacaine postoperatively. Patients were examined in relation to pain severity and opioid analgesic drug need sequences.

Results. The study group needed significantly less opioid than the control group (P<0.01, U=141). The control and study groups were different in first opioid administration time. The control and study groups received first opioid dose in 0-2 and 2-4 hours, respectively.

Conclusion. Bilateral mental nerve blocks with bupivacaine can reduce opioid analgesic need and it has a positive effect on postoperative pain control in mandibular symphyseal fractures.

Opioid-induced constipation: pathophysiology, clinical consequences, and management

Although opioids offer potent analgesia for severe acute and chronic noncancer pain, adverse gastrointestinal effects potentially undermine their clinical utility. In particular, between 40% and 95% of patients develop opioid-induced constipation (OIC). Therefore, there is a consensus that patients should commence laxatives at the start of opioid therapy and continue throughout treatment. Nevertheless, laxatives are not routinely coprescribed with opioids. Even when concurrent laxatives are prescribed, approximately half the patients treated for OIC do not achieve the desired improvement. Moreover, laxatives do not target the underlying cause of OIC (opioid binding to the μ-receptors in the enteric system) and as such are not very effective at managing OIC. The failure of lifestyle modification and laxatives to treat adequately many cases of OIC led to the concurrent use of peripherally acting opioid antagonists (such as methylnaltrexone bromide and naloxone) to reduce the incidence of gastrointestinal adverse events without compromising analgesia. Judicious use of the various options to manage OIC should allow more patients to benefit from opioid analgesia. Therefore, this paper reviews the causes, consequences, and management of OIC to help clinicians optimise opioid analgesia.

The effect of methylnaltrexone on the side effects of intrathecal morphine after orthopedic surgery under spinal anesthesia

Methylnaltrexone is a peripheral opioid receptor antagonist that does not cross the blood-brain barrier; so without interference with pain relief, it could reverse the peripheral opioid side effects such as constipation, pruritus, postoperative ileus, and urinary retention. This study has been designed to evaluate the effect of methylnaltrexone on postoperative side effects of intrathecal morphine. In seventy-two 18- to 55-year-old patients scheduled for elective orthopedic operations under spinal anesthesia, neuraxial blockade was achieved using 10 mg 0.5% hyperbaric bupivacaine and 0.1 mg preservative-free morphine sulfate. The first group (M) received 12 mg methylnaltrexone, while the second group (P) received normal saline, subcutaneously, immediately after spinal block in a randomized, double-blind fashion. There was a significant decrease in the rate of nausea and vomiting in group M, but there was no significant difference in the rate of pruritus or urinary retention between the two groups. Pain score was significantly lower in group M. Respiratory depression or decreased level of consciousness was not reported in any patient. Subcutaneous administration of methylnaltrexone was not effective in decreasing postoperative urinary retention and pruritus, but lowered the rate of nausea and vomiting and pain score after intrathecal bupivacaine and morphine.

Opioid induced bowel disease: a twenty-first century physicians' dilemma. Considering pathophysiology and treatment strategies

The treatment of cancer-associated pain as well as chronic non-cancer-related pain (CNCP) is an increasingly relevant topic in medicine. However, it has long been recognized that opiates can adversely affect many organ systems, most notably the gastrointestinal system. These are referred to as the spectrum of "opioid-induced bowel dysfunction" (OBD) or what we will refer to as "opioid-induced bowel disease" (OIBD) which include constipation, nausea, vomiting, delayed gastric emptying, and gastro-esophageal reflux disease (GERD), and a newer entity known as narcotic bowel syndrome (NBS). Opioid analgesics are increasingly being used for the treatment of cancer pain, non-cancer-associated pain, and postoperative pain. As we achieve our goals towards pain control, we need to be cognizant of and competent in how to prevent and treat OIBD. The basis is due in part to µ-receptor activation, decreasing the peristaltic contraction and leading to sequelae of OIBD. Treatment beyond lifestyle interventional strategy will employ laxatives and stool softeners. However, studies performed while patients were already using laxativies and stool softeners have elicited the necessity of peripherally acting agents such as methylnaltrexone (MNTX) and alvimopan. Patients responded dramatically to both medications, but these studies were limited to patients that were deemed to have advanced illness. Lubiprostone, while different in its mechanism of action from MNTX and alvimopan, has proven effective and should be considered for use in OIBD. Further investigational research will promulgate more information and allow for better and more efficient treatment options for OIBD.

Role of central and peripheral opiate receptors in the effects of fentanyl on analgesia, ventilation and arterial blood-gas chemistry in conscious rats

This study determined the effects of the peripherally restricted μ-opiate receptor (μ-OR) antagonist, naloxone methiodide (NLXmi) on fentanyl (25μg/kg, i.v.)-induced changes in (1) analgesia, (2) arterial blood gas chemistry (ABG) and alveolar-arterial gradient (A-a gradient), and (3) ventilatory parameters, in conscious rats. The fentanyl-induced increase in analgesia was minimally affected by a 1.5mg/kg of NLXmi but was attenuated by a 5.0mg/kg dose. Fentanyl decreased arterial blood pH, pO2 and sO2 and increased pCO2 and A-a gradient. These responses were markedly diminished in NLXmi (1.5mg/kg)-pretreated rats. Fentanyl caused ventilatory depression (e.g., decreases in tidal volume and peak inspiratory flow). Pretreatment with NLXmi (1.5mg/kg, i.v.) antagonized the fentanyl decrease in tidal volume but minimally affected the other responses. These findings suggest that (1) the analgesia and ventilatory depression caused by fentanyl involve peripheral μ-ORs and (2) NLXmi prevents the fentanyl effects on ABG by blocking the negative actions of the opioid on tidal volume and A-a gradient.

Methylnaltrexone use in a seventeen-month-old female with progressive cancer and rectal prolapse

BACKGROUND

Opioid-induced constipation is commonly seen in pediatrics, especially at the end of life. As patients clinically decline, constipation often leads to increased pain and distress, while its enteral treatment becomes more challenging.

METHOD

There is little information about the safety and use of methylnaltrexone in children. We present the case of a 17-month-old girl with progressive leukemia who was at the end of her life and whose severe opioid-induced constipation and rectal prolapse was successfully treated with the μ-opioid-receptor antagonist methylnaltrexone. We selected a lower dose based on our lack of experience with methylnaltrexone in this age group and concern for potential complications given her rectal prolapse.

DISCUSSION

Opioid-induced constipation, abdominal distention, and rectal prolapse caused our patient's most distressing symptoms, even in the context of advanced cancer. A single dose of subcutaneous methylnaltrexone (0.12 mg/kg) resolved her constipation and rectal prolapse within one hour. Although evidence is limited, the drug has successfully been used in pediatric patients with no reported side effects to date. We recommend its use earlier in the course of severe opioid-induced constipation in children unable to tolerate an oral laxation regimen. Prospective research is needed to establish the parameters for use of this effective agent in children who cannot tolerate other regimens.

The in vivo pharmacodynamics of the novel opioid receptor antagonist, TD-1211, in models of opioid-induced gastrointestinal and CNS activity

The in vivo preclinical pharmacodynamic profile of TD-1211, a selective opioid receptor antagonist currently under development for the treatment of opioid-induced constipation, was compared to that of the clinically studied opioid antagonists, naltrexone, alvimopan, and ADL 08-0011 (the primary active metabolite of alvimopan). The oral activity of TD-1211 was evaluated in models of gastrointestinal (GI) and central nervous system (CNS) function in the rat and dog. Oral administration of TD-1211, naltrexone, and ADL 08-0011 reversed loperamide-induced inhibition of gastric emptying and castor oil-induced diarrhea in rats and nonproductive GI circular smooth muscle contractility in dogs. Alvimopan was only efficacious in the castor oil model. Oral administration of naltrexone and ADL 08-0011, but not TD-1211 or alvimopan, was associated with a CNS withdrawal response in morphine-dependent mice, inhibition of morphine-induced anti-nociception in rat and dog hot plate tests, and hypothermia and sedation in dogs. It is concluded that TD-1211 has potent in vivo GI activity, consistent with opioid receptor antagonism, but has no significant CNS activity. The data from these studies support the clinical development of TD-1211 as a novel treatment for opioid-induced GI dysfunction.

Pseudomonas aeruginosa overrides the virulence inducing effect of opioids when it senses an abundance of phosphate

The gut during critical illness represents a complex ecology dominated by the presence of healthcare associated pathogens, nutrient scarce conditions, and compensatory host stress signals. We have previously identified key environmental cues, opioids and phosphate depletion that independently activate the virulence of Pseudomonas aeruginosa. Opioids induce quinolone signal production (PQS), whereas phosphate depletion leads to a triangulated response between MvfR-PQS, pyoverdin, and phosphosensory/phosphoregulatory systems (PstS-PhoB). Yet how P. aeruginosa manages its response to opioids during nutrient scarce conditions when growth is limited and a quorum is unlikely to be achieved is important in the context of pathogenesis in gut during stress. To mimic this environment, we created nutrient poor conditions and exposed P. aeruginosa PAO1 to the specific k-opioid receptor agonist U-50,488. Bacterial cells exposed to the k-opioid expressed a striking increase in virulence- and multi-drug resistance-related genes that correlated to a lethal phenotype in C. elegans killing assays. Under these conditions, HHQ, a precursor of PQS, rather than PQS itself, became the main inducer for pqsABCDE operon expression. P. aeruginosa virulence expression in response to k-opioids required PqsE since ΔPqsE was attenuated in its ability to activate virulence- and efflux pumps-related genes. Extracellular inorganic phosphate completely changed the transcriptional response of PAO1 to the k- opioid preventing pqsABCDE expression, the activation of multiple virulence- and efflux pumps-related genes, and the ability of P. aeruginosa to kill C. elegans. These results indicate that when P. aeruginosa senses resource abundance in the form of phosphate, it overrides its response to compensatory host signals such as opioids to express a virulent and lethal phenotype. These studies confirm a central role for phosphate in P. aeruginosa virulence that might be exploited to design novel anti- virulence strategies.

Pseudomonas aeruginosa virulence expression is directly activated by morphine and is capable of causing lethal gut-derived sepsis in mice during chronic morphine administration

OBJECTIVE

This study was designed to examine the effect of morphine administration on the intestinal mucus barrier and determine its direct effect on the virulence and lethality of Pseudomonas aeruginosa, one of the most frequent pathogens to colonize the gut of critically ill patients.

BACKGROUND DATA

Surgical injury is associated with significant exposure of host tissues to morphine from both endogenous release and its use as a potent analgesic agent. Morphine use in surgical patients exposed to extreme physiologic stress is well established to result in increased infection risk. Although morphine is a known immunosuppressant, whether it directly induces virulence expression and lethality in microbes that colonize the human gut remains unknown.

METHODS

Mice were implanted with a slow release morphine or placebo pellet with and without intestinal inoculation of P. aeruginosa created by direct cecal injection. Mucus production and epithelial integrity was assessed in cecal tissue via Alcian blue staining and histologic analysis. In vivo and in vitro P. aeruginosa virulence expression was examined using reporter strains tagged to the epithelial barrier disrupting protein PA-I lectin. P. aeruginosa chemotaxis toward morphine was also assayed in vitro. Finally, the direct effect of morphine to induce PA-I lectin expression was determined in the absence and presence of methylnaltrexone, a μ opioid receptor antagonist.

RESULTS

Mice intestinally inoculated with P. aeruginosa and implanted with a morphine pellet demonstrated significant suppression of intestinal mucus, disrupted intestinal epithelium, and enhanced mortality; whereas exposure of mice to either systemic morphine or intestinal P. aeruginosa alone enhanced intestinal mucus without mortality, suggesting a shift in P. aeruginosa during morphine exposure to a mucus suppressing, barrier disrupting, and lethal phenotype. Direct exposure of P. aeruginosa to morphine in vitro confirmed that morphine can transform P. aeruginosa to a more virulent phenotype that is attenuated in part by methylnaltrexone.

CONCLUSIONS

Morphine administration shifts intestinal P. aeruginosa to express a virulent phenotype and may play a role in its ability to causes lethal gut-derived sepsis in a susceptible host.

Use of methylnaltrexone for the treatment of opioid-induced constipation in critical care patients

Gastrointestinal dysmotility and constipation are common problems in critical care patients. The majority of critical care patients are treated with opioids, which inhibit gastrointestinal (GI) motility and lead to adverse outcomes. We reasoned that methylnaltrexone (MNTX), a peripheral opioid antagonist approved for the treatment of opioid-induced constipation in patients with advanced illness receiving palliative care when response to laxative therapy has not been sufficient, could improve GI function in critically ill patients. The present study included all patients in our intensive care unit who required rescue medication for GI stasis during the 10-week period from September 1 to November 15, 2009. We compared conventional rescue therapy with subcutaneous MNTX. We performed a retrospective chart review of the 88 nonsurgical critical care patients receiving fentanyl infusions, 15 (17%) of whom met the criteria of absence of laxation within 72 hours of intensive care unit admission despite treatment with senna and sodium docusate. Eight of these 15 patients subsequently received conventional rescue therapy (combination of sodium picosulfate [5 mg] and 2 glycerin suppositories [4-g mold]), and 7 patients received MNTX (subcutaneous injection, 0.15 mg/kg). Laxation occurred within 24 hours in 6 of the 7 MNTX patients (86%) but in none of the 8 patients receiving conventional rescue therapy (P=.001). The median difference in time to laxation between the 2 groups was 3.5 days (P<.001). Although not statistically significant, all 7 patients treated with MNTX, but only 4 of 8 (50%) who received conventional rescue therapy, progressed to full target enteral feeding (P=.08). Intensive care unit mortality was 2 of 7 MNTX patients (29%) vs 4 of 8 (50%) in the standard therapy group (P=.61). We hypothesize that MNTX may play an important role in restoration of bowel function in critically ill patients.

Pain in the ICU: a psychiatric perspective

Pain is abundant in the intensive care unit (ICU). Successful analgesia demands a comprehensive appreciation for the etiologies of pain, vigilant clinical assessment, and personalized treatments. For the critically ill, frequent threats to mental and bodily integrity magnify the experience of pain, challenging clinicians to respond swiftly and thoughtfully. Because pain is difficult to predict and physiologic correlates are not specific, self-report remains the gold standard assessment. When communication is limited by intubation or cognitive deficits, behavioral pain scales prove useful. Patient-tailored analgesia aspires to mitigate suffering while optimizing alertness and cognitive capacity. Mindfulness of the neuropsychiatric features of pain helps the ICU clinician to clarify limits of traditional analgesia and identify alternative approaches to care. Armed with empirical data and clinical practice recommendations to better conceptualize, identify, and treat pain and its neuropsychiatric comorbidities, the authors (psychiatric consultants, by trade) reinforce holistic approaches to pain management in the ICU. After all, without attempts to understand and relieve suffering on all fronts, pain will remain undertreated.

Pharmacology of sedative-analgesic agents: dexmedetomidine, remifentanil, ketamine, volatile anesthetics, and the role of peripheral Mu antagonists

In this article, the authors discuss the pharmacology of sedative-analgesic agents like dexmedetomidine, remifentanil, ketamine, and volatile anesthetics. Dexmedetomidine is a highly selective alpha-2 agonist that provides anxiolysis and cooperative sedation without respiratory depression. It has organ protective effects against ischemic and hypoxic injury, including cardioprotection, neuroprotection, and renoprotection. Remifentanil is an ultra-short-acting opioid that acts as a mu-receptor agonist. Ketamine is a nonbarbiturate phencyclidine derivative and provides analgesia and apparent anesthesia with relative hemodynamic stability. Volatile anesthetics such as isoflurane, sevoflurane, and desflurane are in daily use in the operating room in the delivery of general anesthesia. A major advantage of these halogenated ethers is their quick onset, quick offset, and ease of titration in rendering the patient unconscious, immobile, and amnestic.

The role of morphine in regulation of cancer cell growth

Morphine is considered the "gold standard" for relieving pain and is currently one of the most effective drugs available clinically for the management of severe pain associated with cancer. In addition to its use in the treatment of pain, morphine appears to be important in the regulation of neoplastic tissue. Although morphine acts directly on the central nervous system to relieve pain, its activities on peripheral tissues are responsible for many of the secondary complications. Therefore, understanding the impact, other than pain control, of morphine on cancer treatment is extremely important. The effect of morphine on tumor growth is still contradictory, as both growth-promoting and growth-inhibiting effects have been observed. Accumulating evidence suggests that morphine can affect proliferation and migration of tumor cells as well as angiogenesis. Various signaling pathways have been suggested to be involved in these extra-analgesic effects of morphine. Suppression of immune system by morphine is an additional complication. This review provides an update on the influence of morphine on the growth and migration potential of tumor cells.

Novel opioid antagonists for opioid-induced bowel dysfunction

INTRODUCTION

Adverse effects frequently limit the therapeutic benefits of opioid analgesics. Gastrointestinal adverse effects are common, burdensome, and can compromise the quality of life. It is estimated that up to 81% of patients still report constipation despite regular use of laxatives. Thus, the development of opioid antagonists that selectively target receptors in the gut without affecting central analgesia has provided new perspectives on the treatment of opioid-induced gastrointestinal adverse effects.

AREAS COVERED

In this paper, we review the pathophysiology, prevalence, and burden of opioid-induced bowel dysfunction (OBD). In addition, this study aims to provide a better understanding of the mechanism of action and reviews the efficacy, safety and the latest research on novel opioid antagonists for OBD.

EXPERT OPINION

Two strategies effectively relieve OBD without interfering with centrally mediated analgesia: the administration of opioid antagonists with limited systemic absorption and peripherally acting mu-opioid receptor antagonists (PAMORA) that selectively target mu-receptors in the gastrointestinal tract. Methylnaltrexone and alvimopan are two recently marketed PAMORA and provide a new mechanism-based approach for the treatment of opioid-induced gastrointestinal dysfunction. However, its use in clinical practice is limited by various reasons such as its relatively low response rates and higher costs. Nevertheless, at least four new oral PAMORA (NKTR-118, TD-1211, ADL-7445, and ADL-5945) are under clinical development, further expanding the possibilities for a new paradigm for OBD management.

An update on analgesics

Recent introduction of new analgesics into the clinic is best described as a slow process with activity classified into two main areas: improving analgesic efficacy/potency and reducing side-effect profile. This review article describes some of the recent advances with an emphasis on use in the acute setting. In this respect, opioids continue to be the mainstay (but not the only) analgesic and there have been important improvements in their clinical effect profile. For example, tapentadol has been introduced as a mixed opioid and norepinephrine uptake inhibitor which, unlike tramadol, does not require metabolic activation and does not suffer from isomer-dependent pharmacodynamics. Opioid antagonists have received much attention recently either used alone, methylnaltrexone (s.c) or alvimopan (p.o), or in combination, Targinact (oxycodone/naloxone), and appear to be effective in reducing opioid side-effects such as those in the gastrointestinal tract. Other agents where there has been recent development include the use of gabapentin, methylxanthines, and local anaesthetics. An interesting area of translation of basic research is in the inhibition of breakdown of endogenous opioids with opiorphin, targeting of the endocannabinoid system, and the use of ampakines to obtund opioid-induced side-effects. It is clear that there is still much work to be done, but the need for highly efficacious analgesics with good side-effect profile remains.

Opioid antagonists for prevention and treatment of opioid-induced gastrointestinal effects

PURPOSE OF REVIEW

The therapeutic action of opioid analgesics is compromised by peripheral adverse effects, among which constipation is the most disabling as laxatives often fail to provide satisfactory relief. This review highlights recent advances in the specific control of opioid-induced constipation by opioid receptor antagonists with limited systemic bioavailability or a peripherally restricted site of action.

RECENT FINDINGS

The specific management of opioid-induced bowel dysfunction is currently based on three drug entities: oral alvimopan for the shortening of postoperative ileus associated with opioid-induced pain control after bowel resection, subcutaneous methylnaltrexone for the reduction of opioid-induced constipation in patients with advanced illness, and a fixed combination of oral prolonged-release naloxone with prolonged-release oxycodone for the treatment of noncancer and cancer pain. All three drug entities have been shown to attenuate opioid-induced motor stasis in the gut with a favorable adverse effect profile, while the analgesic effect of opioids remains unabated.

SUMMARY

The availability of opioid receptor antagonists with restricted access to the central nervous system provides a novel opportunity to specifically control opioid-induced constipation and other peripheral adverse effects of opioid analgesics. Further studies are needed to evaluate the long-term efficacy, safety and cost-effectiveness of this approach.

Effect of perioperative opioids on cancer recurrence: a hypothesis

The possibility that anesthetic drugs can influence cancer recurrence rate is a subject of recent interest. Based on early in vitro data demonstrating opiates on breast cancer xenografts and two recent epidemiologic studies suggesting differences in recurrence rates in both breast and prostate cancer contingents dependent on whether patients received a combined regional-general anesthetic or a general anesthetic with opioid analgesia, there has been recent interest in the role of the micro-opioid receptor (MOR) in angiogenesis and oncogenic signaling. We recently demonstrated that morphine causes reciprocal transactivation of the MOR and VEGF receptors and that MOR-knockout mice do not develop significant tumors when injected with lung cancer cells as do their wild-type controls. Furthermore, infusion of the peripheral MOR antagonist methylnaltrexone markedly attenuates tumor growth in experimental mouse models. These experimental data support the hypothesis that opioids affect tumor progression and suggest the MOR as a potential target for chemotherapeutic drugs.

The novel role of the mu opioid receptor in lung cancer progression: a laboratory investigation

BACKGROUND

The possibility that μ opioid agonists can influence cancer recurrence is a subject of recent interest. Epidemiologic studies suggested that there were differences in cancer recurrence in breast and prostate cancer contingent on anesthetic regimens. In this study, we identify a possible mechanism for these epidemiologic findings on the basis of μ opioid receptor (MOR) regulation of Lewis lung carcinoma (LLC) tumorigenicity in cell and animal models.

METHODS

We used human lung tissue and human non-small cell lung cancer (NSCLC) cell lines and evaluated MOR expression using immunoblot and immunohistochemical analysis. LLC cells were treated with the peripheral opioid antagonist methylnaltrexone (MNTX) or MOR shRNA and evaluated for proliferation, invasion, and soft agar colony formation in vitro and primary tumor growth and lung metastasis in C57BL/6 and MOR knockout mice using VisEn fluorescence mediated tomography imaging and immunohistochemical analysis.

RESULTS

We provide several lines of evidence that the MOR may be a potential target for lung cancer, a disease with high mortality and few treatment options. We first observed that there is ∼5- to 10-fold increase in MOR expression in lung samples from patients with NSCLC and in several human NSCLC cell lines. The MOR agonists morphine and [D-Ala(2), N-MePhe(4), Gly-ol]-enkephalin (DAMGO) increased in vitro LLC cell growth. Treatment with MNTX or silencing MOR expression inhibited LLC invasion and anchorage-independent growth by 50%-80%. Injection of MOR silenced LLC lead to a ∼65% reduction in mouse lung metastasis. In addition, MOR knockout mice do not develop significant tumors when injected with LLC in comparison with wild-type controls. Finally, continuous infusion of the peripheral opioid antagonist MNTX attenuates primary LLC tumor growth and reduces lung metastasis.

CONCLUSIONS

Taken together, our data suggest a possible direct effect of opiates on lung cancer progression, and provide a plausible explanation for the epidemiologic findings. Our observations further suggest a possible therapeutic role for opioid antagonists.

The effects of methylnaltrexone alone and in combination with acutely administered codeine on gastrointestinal and colonic transit in health

BACKGROUND

The short-term effects of methylnaltrexone (MNTX), a peripherally acting mu-opioid receptor antagonist, on gastrointestinal and colonic transit remain unclear.

AIM

To compare the effects of placebo, codeine, subcutaneous (s.c.) MNTX and codeine with s.c. MNTX on gastrointestinal and colonic transit of solids in healthy humans.

METHODS

In a randomized, parallel-group, double-blind, placebo-controlled trial of 48 healthy volunteers, effects of 6 consecutive days of placebo [s.c. and p.o. (orally), n = 8], codeine (p.o. 30 mg q.d.s., n = 8), MNTX (s.c. 0.30 mg/kg, n = 16) and combined MNTX and codeine (same doses and routes, n = 16) on gastrointestinal and colonic transit were assessed. A validated scintigraphic method was used to measure transit during the last 48 h of treatment. Bowel function was estimated during treatment as well as 1 week preceding treatment using standard diaries. Analysis of covariance was used to assess treatment effects.

RESULTS

Codeine delayed colonic transit [geometric centre at 24 h (P = 0.04) and ascending colon t(1/2) (P = 0.02)] and reduced stool frequency (P = 0.002), but had no effect on stool form. MNTX did not affect transit, stool frequency or stool form, either alone or with codeine (P > 0.3). No drug interaction effects were detected (P > 0.15).

CONCLUSION

Methylnaltrexone does not alter gastrointestinal or colonic transit and does not reverse acute codeine-associated delayed gut transit in health.