Low-dose oral naloxone reverses opioid-induced constipation and analgesia

Managing Severe Cancer Pain with Oxycodone/Naloxone Treatment: A Literature Review Update

Severe cancer pain substantially affects patients' quality of life, increasing the burden of the disease and reducing the disability-adjusted life years. Although opioid analgesics are effective, they may induce opioid-induced bowel dysfunction (OIBD). Oxycodone/naloxone combination therapy has emerged as a promising approach to mitigate opioid-induced constipation (OIC) while providing effective pain relief. This review provides an updated analysis of the literature of the last decade regarding the use of oxycodone/naloxone in the management of severe cancer pain. Through a comprehensive search of databases, studies focusing on the efficacy, safety, and patient experience of oxycodone/naloxone's prolonged release in severe cancer pain management were identified. Furthermore, the literature discusses the mechanism of action of naloxone in mitigating OIC without compromising opioid analgesia. Overall, the evidence suggests that oxycodone/naloxone combination therapy offers a valuable option for effectively managing severe cancer pain while minimizing opioid-induced constipation, thereby improving patients' quality of life. However, further research is needed to optimize dosing regimens, evaluate long-term safety, and assess patient outcomes in diverse cancer populations.

Effect of oral naloxone on opioid-induced constipation in methadone maintenance treatment patients, a double-blind, placebo-control, clinical trial

BACKGROUND

Opioid-induced constipation (OIC) is the most prevalent side effect of methadone maintenance therapy (MMT). Naloxone could reduce the OIC.

METHOD

Fifty-six MMT cases (< 75 mg/day methadone, > 3 months) were entered randomly into four groups of a trial. They received placebo or naloxone tablets (0.5, 2, or 4 mg/day) once a day for 2 weeks. They continued their conventional laxative. Their constipation and opiate withdrawal (OWS) were evaluated by the Bristol Stool Form Scale (stool consistency and frequency), Patient Assessment of Constipation Symptoms (PAC-SYM) questionnaire, Constipation Scoring System (CSS), and the Subjective Opiate Withdrawal Scale (SOWS) before starting treatment and at the end of the first and second weeks.

RESULTS

The dose of 4 mg/day naloxone was excluded from the study due to severe OWS. The precipitants of groups had similar ages, methadone dose and duration, laxative use, and constipation scores at the start of the trial. However, 2 mg of naloxone could change the stool consistency (PV = 0.0052) and frequency (P = 0.0133), 0.5 mg/day dose only improved the stool consistency (P = 0.0016). The patients' CSS and PAC-SYM scores were reduced by naloxone after the 1st week of treatment. However, there was no significant difference in the mean score of SOWS at different assessment times and groups. Also, 3 and 4 cases of 0.5 and 2 mg/day groups, respectively, withdrew from the study due to OWS.

CONCLUSION

Oral naloxone at doses of 0.5 and 2 mg/day was significantly more effective than placebo on OIC in MMT. However, the dose of 4 mg induced intolerable OWS.

Naldemedine is associated with earlier defecation in critically ill patients with opioid-induced constipation: A retrospective, single-center cohort study

INTRODUCTION

There are few reports describing the association of naldemedine with defecation in critically ill patients with opioid-induced constipation. The purpose of this study was to determine whether naldemedine is associated with earlier defecation in critically ill patients with opioid-induced constipation.

METHODS

In this retrospective cohort study, patients admitted to the Intensive Care Unit (ICU) without defecation for 48 hours while receiving opioids were eligible for enrollment. The primary endpoint was the time of the first defecation within 96 hours after inclusion. Secondary endpoints included presence of diarrhea, duration of mechanical ventilation, ICU length of stay, ICU mortality, and in-hospital mortality. The Cox proportional hazard regression analysis with time-dependent covariates was used to evaluate the association naldemedine with earlier defecation.

RESULTS

A total of 875 patients were enrolled and were divided into 63 patients treated with naldemedine and 812 patients not treated. Defecation was observed in 58.7% of the naldemedine group and 48.8% of the no-naldemedine group during the study (p = 0.150). The naldemedine group had statistically significantly prolonged duration of mechanical ventilation (8.7 days vs 5.5 days, p < 0.001) and ICU length of stay (11.8 days vs 9.2 days, p = 0.001) compared to the no-naldemedine group. However, the administration of naldemedine was significantly associated with earlier defecation [hazard ratio:2.53; 95% confidence interval: 1.71-3.75, p < 0.001].

CONCLUSION

The present study shows that naldemedine is associated with earlier defecation in critically ill patients with opioid-induced constipation.

Peripherally-active mu-opioid receptor antagonists for constipation in critically ill patients receiving opioids: A case-series and a systematic review and meta-analysis of the literature

BACKGROUND

Constipation is frequent in critically ill patients, and potentially related to adverse outcomes. Peripherally-active mu-opioid receptor antagonists (PAMORAs) are approved for opioid-induced constipation, but information on their efficacy and safety in critically ill patients is limited. We present a single-center, retrospective, case-series of the use of naldemedine for opioid-associated constipation, and we systematically reviewed the use of PAMORAs in critically ill patients.

METHODS

Case-series included consecutive mechanically-ventilated patients; constipation was defined as absence of bowel movements for >3 days. Naldemedine was administered after failure of the local laxation protocol. Systematic review: PubMed was searched for studies of PAMORAs to treat opioid-induced constipation in adult critically ill patients.

PRIMARY OUTCOMES

time to laxation, and number of patients laxating at the shortest follow-up.

SECONDARY OUTCOMES

gastric residual volumes and adverse events.

KEY RESULTS

A total of 13 patients were included in the case-series; the most common diagnosis was COVID-19 ARDS. Patients had their first bowel movement 1 [0;2] day after naldemedine. Daily gastric residual volume was 725 [405;1805] before vs. 250 [45;1090] mL after naldemedine, p = 0.0078. Systematic review identified nine studies (two RCTs, one prospective case-series, three retrospective case-series and three case-reports). Outcomes were similar between groups, with a trend toward a lower gastric residual volume in PAMORAs group.

CONCLUSIONS & INFERENCES

In a highly-selected case-series of patients with refractory, opioid-associated constipation, naldemedine was safe and associated to reduced gastric residuals and promoting laxation. In the systematic review and meta-analysis, the use of PAMORAs (mainly methylnaltrexone) was safe and associated with a reduced intolerance to enteral feeding but no difference in the time to laxation.

Emerging drug interaction prediction enabled by a flow-based graph neural network with biomedical network

Drug-drug interactions (DDIs) for emerging drugs offer possibilities for treating and alleviating diseases, and accurately predicting these with computational methods can improve patient care and contribute to efficient drug development. However, many existing computational methods require large amounts of known DDI information, which is scarce for emerging drugs. Here we propose EmerGNN, a graph neural network that can effectively predict interactions for emerging drugs by leveraging the rich information in biomedical networks. EmerGNN learns pairwise representations of drugs by extracting the paths between drug pairs, propagating information from one drug to the other, and incorporating the relevant biomedical concepts on the paths. The edges of the biomedical network are weighted to indicate the relevance for the target DDI prediction. Overall, EmerGNN has higher accuracy than existing approaches in predicting interactions for emerging drugs and can identify the most relevant information on the biomedical network.

Effects of Electroacupuncture for Opioid-Induced Constipation in Patients With Cancer in China: A Randomized Clinical Trial

IMPORTANCE

Opioid-induced constipation (OIC) is prevalent among patients treated with opioids for cancer pain. Safe and effective therapies for OIC in patients with cancer remain an unmet need.

OBJECTIVE

To determine the efficacy of electroacupuncture (EA) for OIC in patients with cancer.

DESIGN, SETTING, AND PARTICIPANTS

This randomized clinical trial was conducted at 6 tertiary hospitals in China among 100 adult patients with cancer who were screened for OIC and enrolled between May 1, 2019, and December 11, 2021.

INTERVENTIONS

Patients were randomized to receive 24 sessions of EA or sham electroacupuncture (SA) over 8 weeks and then were followed up for 8 weeks after treatment.

MAIN OUTCOMES AND MEASURES

The primary outcome was the proportion of overall responders, defined as patients who had at least 3 spontaneous bowel movements (SBMs) per week and an increase of at least 1 SBM from baseline in the same week for at least 6 of the 8 weeks of the treatment period. All statistical analyses were based on the intention-to-treat principle.

RESULTS

A total of 100 patients (mean [SD] age, 64.4 [10.5] years; 56 men [56.0%]) underwent randomization; 50 were randomly assigned to each group. Among them, 44 of 50 patients (88.0%) in the EA group and 42 of 50 patients (84.0%) in the SA group received at least 20 (≥83.3%) sessions of treatment. The proportion of overall responders at week 8 was 40.1% (95% CI, 26.1%-54.1%) in the EA group and 9.0% (95% CI, 0.5%-17.4%) in the SA group (difference between groups, 31.1 percentage points [95% CI, 14.8-47.6 percentage points]; P < .001). Compared with SA, EA provided greater relief for most OIC symptoms and improved quality of life among patients with OIC. Electroacupuncture had no effects on cancer pain and its opioid treatment dosage. Electroacupuncture-related adverse events were rare, and, if any, all were mild and transient.

CONCLUSIONS AND RELEVANCE

This randomized clinical trial found that 8-week EA treatment could increase weekly SBMs with a good safety profile and improve quality of life for the treatment of OIC. Electroacupuncture thus provided an alternative option for OIC in adult patients with cancer.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03797586.

Sustained drug delivery strategies for treatment of common substance use disorders: Promises and challenges

Substance use disorders (SUDs) are a leading cause of death and other ill health effects in the United States and other countries in the world. Several approaches ranging from detoxification, behavioral therapy, and the use of antagonists or drugs with counter effects are currently being applied for its management. Amongst these, drug therapy is the mainstay for some drug abuse incidences, as is in place specifically for opioid abuse or alcohol dependence. The severity of the havocs observed with the SUDs has triggered constant interest in the discovery and development of novel medications as well as suitable or most appropriate methods for the delivery of these agents. The chronic need of such drugs in users warrants the need for their prolonged or sustained systemic availability. Further, the need to improve patient tolerance to medication, limit invasive drug use and overall treatment outcome are pertinent considerations for embracing sustained release designs for medications used in managing SUDs. This review aims to provide an overview on up-to-date advances made with regards to sustained delivery systems for the drugs for treatment of different types of SUDs such as opioid, alcohol, tobacco, cocaine, and cannabis use disorders. The clinical relevance, promises and the limitations of deployed sustained release approaches along with future opportunities are discussed.

Acute Hydronephrosis Secondary to Methadone-Induced Constipation

Opioid-induced constipation is a significant medical problem accounting for over 40% to 60% of patients without cancer receiving opioids. We report a unique case of a 71-year-old male with a history of opioid use disorder now on methadone maintenance presenting with severe opioid-induced constipation and fecal impaction causing extrinsic compression on the right-sided ureter resulting in right hydronephrosis and hydroureter that improved with aggressive bowel regime with the stool softener, laxatives and enemas.

Methadone alone can predispose to hydroureter with hydronephrosis due to external compression from the severe intestinal dilation secondary to opioid-induced constipation.

The effect of opioids on gastrointestinal function in the ICU

Gastrointestinal (GI) dysfunction is common in the critical care setting and is highly associated with clinical outcomes. Opioids increase the risk for GI dysfunction and are frequently prescribed to reduce pain in critically ill patients. However, the role of opioids in GI function remains uncertain in the ICU. This review aims to describe the effect of opioids on GI motility, their potential risk of increasing infection and the treatment of GI dysmotility with opioid antagonists in the ICU setting.

Analysis of Predictive Factors for Diarrhea after the Administration of Naldemedine

Naldemedine (NAL), a peripherally acting μ-opioid receptor antagonist, is effective for opioid-induced constipation (OIC). However, diarrhea is the most common adverse event. We investigated the incidence of NAL-induced diarrhea in patients who started NAL at Nagasaki University Hospital between June 2017 and March 2019. Predictors of NAL-induced diarrhea were analyzed using a multivariate logistic regression model. Two hundred and forty-two patients were included in the present study, and NAL-induced diarrhea was observed in 17.8% (43 patients). The results of multiple logistic regression analyses identified the administration of opioid analgesics for 8 d or longer before the initiation of NAL (odds ratio (OR): 2.20, 95% confidence interval (95% CI): 1.04-4.64, p = 0.039), the combination of a laxative (OR: 2.22, 95%CI: 1.03-4.81, p = 0.042), and the combination of CYP3A4 inhibitors (strong/moderate) (OR: 2.80, 95%CI: 1.02-7.67, p = 0.045) as risk factors. Therefore, the development of diarrhea needs to be considered in patients with these risk factors. Furthermore, diarrhea may be controlled by the initiation of NAL within 7 d of opioid analgesics and, where possible, the discontinuation of or change in the combination of moderate or strong CYP3A4 inhibitors.

Efficacy and Safety of Peripherally Acting μ-Opioid Receptor Antagonist (PAMORAs) for the Management of Patients With Opioid-Induced Constipation: A Systematic Review

In treating chronic and acute pain, opioids are widely used. Although they do provide analgesia, their usage does come with adverse events (AEs). One of the most burdensome is opioid-induced bowel dysfunction, and more specifically opioid-induced constipation (OIC). The pathogenesis of these AEs is well known as the consequence of the action of opioids on m-receptors in the enteric nervous system. In recent years, medicines counteracting this specific action at the receptors have been registered for clinical use: the peripherally acting μ-opioid receptor antagonists (PAMORAs). The knowledge of their comparative efficacy and tolerability is very important for physicians and patients in opioid therapy. This systematic review of the existing literature on PAMORAs aimed to study the relative clinical advantages and disadvantages. The most important data banks, including "PubMed," "Embase," "CT.gov," "ICTRP" and "CINAHL" were used to find the published material on PAMORAs. The selected publications were examined to systematically analyze the efficacy and safety of the four existing PAMORAs. All of the medications are superior to placebo in reducing OIC. There are few published data on alvimopan used to treat OIC, and it is only indicated for the treatment of post-abdominal surgery ileus. Methylnaltrexone is studied mainly in its subcutaneous (SC) formulation. When used in its oral formulation, it seems more rapid than naloxegol and placebo in the reduction of OIC. Naldemedine is able to produce more spontaneous bowel movements (SBMs) when compared to alvimopan and naloxegol. Tolerability was found to be similar for all of them. In particular, they affect the gastrointestinal tract (GI), with flatulence and diarrhea, especially at high dosages. For some of them, nasopharyngitis and abdominal pain were observed as treatment adverse effects (TEAs). Several cardiovascular TEAs were reported after methylnaltrexone use, but it is not clear whether they were consequences of the drug or related to the general conditions of the patients. Considering the existing data, naloxegol and naldemedine seem to be the best choices, with a higher number of spontaneous bowel movements following naldemedine administration.

TLR4 biased small molecule modulators

Biased pharmacological modulators provide potential therapeutic benefits, including greater pharmacodynamic specificity, increased efficiency and reduced adverse effects. Therefore, the identification of such modulators as drug candidates is highly desirable. Currently, attention was mainly paid to biased signaling modulators targeting G protein-coupled receptors (GPCRs). The biased signaling modulation of non-GPCR receptors has yet to be exploited. Toll-like receptor 4 (TLR4) is one such non-GPCR receptor, which involves MyD88-dependent and TRIF-dependent signaling pathways. Moreover, the dysregulation of TLR4 contributes to numerous diseases, which highlights the importance of biased modulator development targeting TLR4. In this review, we aim to provide an overview of the recent progress in the discovery of biased modulators of TLR4. The challenges and methods for the discovery of TLR4 biased modulators are also outlined. Small molecules biasedly modulating the TLR4 signaling axis not only provide probes to fine-tune receptor conformation and signaling but also provide an opportunity to identify promising drug candidates. The discovery of biased modulators of TLR4 would provide insight for the future development of biased modulators for other non-GPCR receptors.

Anti-diarrheal therapeutic potential of diminazene aceturate stimulation of the ACE II/Ang-(1-7)/Mas receptor axis in mice: A trial study

The angiotensin (Ang) II converting enzyme (ACE II) pathway has recently been shown to be associated with several beneficial effects on the body, especially on the cardiac system and gastrointestinal tract. ACE II is responsible for converting Ang II into the active peptide Ang-(1-7), which in turn binds to a metabotropic receptor, the Mas receptor (MasR). Recent studies have demonstrated that Diminazene Aceturate (DIZE), a trypanosomicide used in animals, activates the ACE II pathway. In this study, we aimed to evaluate the antidiarrheal effects promoted by the administration of DIZE to activate the ACE II/Ang-(1-7)/MasR axis in induced diarrhea mice models. The results show that activation of the ACE II pathway exerts antidiarrheal effects that reduce total diarrheal stools and enteropooling. In addition, it increases Na⁺/K⁺-ATPase activity and reduces gastrointestinal transit and thus inhibits contractions of intestinal smooth muscle; decreases transepithelial electrical resistance, epithelial permeability, PGE2-induced diarrhea, and proinflammatory cytokines; and increases anti-inflammatory cytokines. Enzyme-linked immunosorbent assay (ELISA) demonstrated that DIZE, when activating the ACE II/Ang-(1-7)/MasR axis, can still interact with GM1 receptors, which reduces cholera toxin-induced diarrhea. Therefore, activation of the ACE II/Ang-(1-7)/MasR axis can be an important pharmacological target for the treatment of diarrheal diseases.

Peripherally Acting μ-Opioid Receptor Antagonists in the Management of Postoperative Ileus: a Clinical Review

Postoperative ileus (POI) and constipation are common secondary effects of opioids and carry significant clinical and economic impacts. μ-Opioid receptors mediate opioid analgesia in the central nervous system (CNS) and gastrointestinal-related effects in the periphery. Peripherally acting μ-opioid receptor antagonists (PAMORAs) block the peripheral effects of opioids in the gastrointestinal tract, while maintaining opioid analgesia in the CNS. While most are not approved for POI or postoperative opioid-induced constipation (OIC), PAMORAs have a potential role in these settings via their selective effects on the μ-opioid receptor. This review will discuss recent clinical trials evaluating the safety and efficacy of PAMORAs, with a focus on alvimopan (Entereg^®) and methylnaltrexone (Relistor^®) in patients with POI or postoperative OIC. We will characterize potential factors that may have impacted the efficacy observed in phase 3 trials and discuss future directions for the management and treatment of POI.

Efficacy and Safety of Peripherally Acting Mu-Opioid Receptor Antagonists for the Treatment of Opioid-Induced Constipation: A Bayesian Network Meta-analysis

OBJECTIVE

To assess the efficacy and safety of peripherally acting mu-opioid receptor antagonists (PAMORAs) for the treatment of opioid-induced constipation (OIC).

METHODS

Randomized controlled trials (RCTs) were searched for OIC therapy comparing PAMORAs with placebo. Both a pairwise and network meta-analysis were performed. The surface under the cumulative ranking area (SUCRA) was used to determine the efficacy and safety of OIC treatment using different PAMORAs.

RESULTS

The primary target outcome was a response that achieves an average of three or more bowel movements (BMs) per week. In the network meta-analysis, four PAMORAs (naldemedine, naloxone, methylnaltrexone, and alvimopan) showed a better BM response than the placebo. Naldemedine was ranked first (odds ratio [OR] = 2.8, 95% credible interval [CrI] = 2-4.5, SUCRA = 89.42%), followed by naloxone (OR = 2.9, 95% CrI = 1.6-5.3, SUCRA = 87.44%), alvimopan (OR = 2.2, 95% CrI = 1.3-3.5, SUCRA = 68.02%), and methylnaltrexone (OR = 1.7, 95% CrI = 1.0-2.8, SUCRA = 46.09%). There were no significant differences in safety found between the PAMORAs and the placebo.

CONCLUSIONS

We found that PAMORAs are effective and can be safely used for the treatment of OIC. In network meta-analysis, naldemedine and naloxone appear to be the most effective PAMORAs for the treatment of OIC.

Cannabinoid CB2 Receptor Activation Attenuates Fentanyl-Induced Respiratory Depression

Introduction: Overdose fatalities associated with the opioid epidemic are predictably attributable to drug-induced respiratory depression. In terms of illicit opioid abuse, fentanyl is the synthetic opioid responsible for the largest number of overdose deaths. There is, therefore, an urgent need to identify safe and effective therapeutics that can attenuate fentanyl-induced respiratory depression. Identification of effective alternate analgesic strategies that lessen the respiratory depression associated with narcotics would also help improve current strategies for pain management. Our laboratory recently reported that the G protein-biased CB₂ cannabinoid receptor agonist LY2828360 suppressed chemotherapy-induced neuropathic nociception and attenuated both morphine tolerance and physical dependence in paclitaxel-treated mice. However, the impact of LY2828360 on other undesirable side effects of opioids, such as opioid-induced respiratory depression, remains unknown. Materials and Methods: We used whole-body plethysmography to assess the impact of the CB₂ cannabinoid agonist LY2828360 on fentanyl-induced respiratory depression using wild-type (WT) and CB₂ knockout (CB₂KO) mice. Results: Fentanyl reduced minute ventilation and respiratory frequency without altering tidal volume in both WT and CB₂KO mice. In WT mice, the high dose of fentanyl (0.2 mg/kg intraperitoneal [i.p.]) produced a greater suppression of respiratory parameters compared with the low dose of fentanyl (0.1 mg/kg i.p.). Coadministration of a behaviorally active dose of LY2828360 (3 mg/kg i.p.) with fentanyl (0.2 mg/kg i.p.) attenuated fentanyl-induced respiratory depression in WT mice. Notably, LY2828360 (3 mg/kg i.p.) did not attenuate fentanyl-induced respiratory depression in CB₂KO mice, consistent with mediation by CB₂ receptors. Moreover, LY2828360 (3 mg/kg i.p.) alone lacked intrinsic effects on respiratory parameters in either WT or CB₂KO mice. Conclusion: The combination of a CB₂ agonist with fentanyl may represent a safer adjunctive therapeutic strategy compared with a narcotic analgesic alone by attenuating the development of opioid-induced respiratory depression. Moreover, the CB₂ agonist, administered alone, did not alter respiration. Our findings suggest that the CB₂ cannabinoid agonist LY2828360 may provide CB₂-mediated protection against fentanyl-induced respiratory depression, a detrimental and unwanted side effect of opioid use and abuse.

Intranasal Low-Dose Naltrexone Against Opioid Side Effects: A Preclinical Study

Opioids are broad spectrum analgesics that are an integral part of the therapeutic armamentarium to combat pain in the clinical practice. Unfortunately, together with analgesia, a number of adverse effects can occur such as nausea, vomiting, constipation, gastrointestinal alterations and cognitive impairments. Naltrexone is a competitive antagonist of opioid receptors commonly used to treat opioid addiction; its oral use against agonists side effects is limited by the decrease of opioids-therapeutic efficacy and own adverse effects. The intranasal delivery of naltrexone could offer a quick and effective achievement of CNS based on extracellular mechanisms including perineural and perivascular transport. The aim of the study was to test the efficacy of intranasal low-dose naltrexone in reducing intraperitoneal morphine and oxycodone side effects in rodents. In mice, 1 μg naltrexone intranasally administered 30 min before opioids reduced cognitive impairments and motor alteration induced by 10 mg kg^-1 morphine and 60 mg kg^-1 oxycodone in the Passive avoidance and Rota rod tests, respectively. Moreover, naltrexone rebalanced opioid-induced reduction of the intestinal transit and latency of feces expulsion as well as food intake inhibition. Importantly, 1 μg naltrexone instillation did not block analgesia as demonstrated by the Hot plate test. In rats, intranasal naltrexone counteracted the opioid-induced pica phenomenon related to emesis and increased water and palatable food intake. The effects were comparable to that achieved by metoclopramide used as reference drug. Treatments did not influence body weight. Lastly, the safety of the intranasal delivery has been checked by hematoxylin-eosin staining that did not show histological alterations of the nasal cavity. In conclusion, intranasal low-dose naltrexone counteracted morphine and oxycodone induced gastrointestinal and CNS side effects without impairing opioid analgesia. It is a candidate to be a valid clinical strategy deserving deep analysis.

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.

Systematic review with meta-analysis: efficacy and safety of treatments for opioid-induced constipation

BACKGROUND

When opioid-induced constipation is treated with centrally acting opioid antagonists, there may be opioid withdrawal or aggravation of pain due to inhibition of μ-opioid analgesia. This led to the development of peripherally acting μ-opioid receptor antagonists (PAMORAs).

AIM

To evaluate the efficacy of available PAMORAs and other approved or experimental treatments for relieving constipation in patients with opioid-induced constipation, based on a systematic review and meta-analysis of published studies.

METHODS

A search of MEDLINE, EMBASE and EBM Reviews Cochrane Central Register of Controlled Trials was completed in July 2019 for randomised trials compared to placebo. FDA approved doses or highest studied dose was evaluated. Efficacy was based on diverse endpoints, including continuous variables (the bowel function index, number of spontaneous bowel movements and stool consistency based on Bristol Stool Form Scale), or responder analysis (combination of >3 spontaneous bowel movements or complete spontaneous bowel movements plus 1 spontaneous bowel movement or complete spontaneous bowel movements, respectively, over baseline [so-called FDA endpoints]). Adverse effects evaluated included central opioid withdrawal, serious adverse events, abdominal pain and diarrhoea.

RESULTS

We included 35 trials at low risk of bias enrolling 13 566 patients. All PAMORAs demonstrated efficacy on diverse patient response endpoints. There was greater efficacy with approved doses of the PAMORAs (methylnaltrexone, naloxegol and naldemidine), with lower efficacy or lower efficacy and greater adverse effects with combination oxycodone with naloxone, lubiprostone and linaclotide.

CONCLUSIONS

Therapeutic response in opioid-induced constipation is best achieved with the PAMORAs, methylnaltrexone, naloxegol and naldemidine, which are associated with low risk of serious adverse events.

Inhibitory transmission in the bed nucleus of the stria terminalis in male and female mice following morphine withdrawal

The United States is experiencing an opioid crisis imposing enormous fiscal and societal costs and driving the staggering overdose death rate. While prescription opioid analgesics are essential for treating acute pain, cessation of use in individuals with a physical dependence induces an aversive withdrawal syndrome that promotes continued drug use to alleviate/avoid these symptoms. Additionally, repeated bouts of withdrawal often lead to an increased propensity for relapse. Understanding the neurobiology underlying withdrawal is essential for providing novel treatment options to alleviate physiological and affective components accompanying the cessation of opiate use. Here, we administered morphine and precipitated withdrawal with naloxone to investigate behavioral and cellular responses in C57BL/6J male and female mice. Following 3 days of administration, both male and female mice demonstrated sensitized withdrawal symptoms. Since the bed nucleus of the stria terminalis (BNST) plays a role in mediating withdrawal-associated behaviors, we examined plastic changes in inhibitory synaptic transmission within this structure 24 hours following the final precipitated withdrawal. In male mice, morphine withdrawal increased spontaneous GABAergic signaling compared with controls. In contrast, morphine withdrawal decreased spontaneous GABAergic signaling in female mice. Intriguingly, these opposing GABAergic effects were contingent upon activity-dependent dynamics within the ex vivo slice. Our findings suggest that male and female mice exhibit some divergent cellular responses in the BNST following morphine withdrawal, and alterations in BNST inhibitory signaling may contribute to the expression of behaviors following opioid withdrawal.

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.

Prevention and management of diarrhea associated with naldemedine among patients receiving opioids: a retrospective cohort study

BACKGROUND

Naldemedine, a novel peripherally-acting mu-opioid receptor antagonist, has improved opioid-induced constipation in randomized controlled trials. The most frequent adverse event of naldemedine is diarrhea, which can cause abdominal pain and often leads to treatment discontinuation. We aimed to identify risk factors and appropriate management strategies for key adverse events including diarrhea associated with naldemedine, since those have not been extensively studied.

METHODS

We conducted a multi-center retrospective cohort study. Eligible patients had cancer, had undergone palliative care at participating centers, had been prescribed regular opioids, and had taken at least one dose of naldemedine between June 2017 and March 2018. The primary endpoint was the incidence of diarrhea according to baseline characteristics. Secondary endpoints included the duration of naldemedine administration, daily defecation counts before and after starting naldemedine, duration and severity of diarrhea as an adverse event of naldemedine, other adverse events, and the incidence of constipation within 7 days after recovery from diarrhea. We defined patients who started naldemedine within three days of starting a regularly prescribed opioid as the early group, and the remainder as the late group.

RESULTS

Among 103 patients who received naldemedine, 98 fulfilled the eligibility criteria. The median age was 68 years and 48% of the patients were female. Median performance status was 3, and the median oral intake was 50%. The median duration of naldemedine administration and overall survival were 25 and 64 days, respectively. The incidence of diarrhea in the early group (n = 26) was significantly lower than in the late group (n = 72) (3.9% vs. 22.2%, p = 0.02). Daily defecation counts increased after late (median 0.43 to 0.88, p < 0.001), but remained stable after early naldemedine administration (median 1.00 to 1.00, p = 0.34). Constipation after the diarrhea was resolved was common (53%), especially among patients who stopped naldemedine (78%). The diarrhea was improved within three days in 92% of patients who stopped other laxatives.

CONCLUSIONS

The early administration of naldemedine is beneficial because it reduces adverse events including diarrhea. Diarrhea caused by naldemedine can be effectively managed by stopping other laxatives while continuing naldemedine.

Opioid-Induced Constipation in Oncological Patients: New Strategies of Management

OPINION STATEMENT

Cancer-associated pain has traditionally been treated with opioid analgesics, often in escalating doses. Opioid-induced constipation (OIC) is a common problem associated with chronic use of opioid analgesics. Typical treatment strategies to alleviate constipation are based on dietary changes, exercise, and laxatives. However, laxatives have a nonspecific action and do not target underlying mechanisms of OIC. This article will review prevalent, clinical presentation and recommendations for the treatment of OIC. An independent literature search was carried out by the authors. We reviewed the literature for randomized controlled trials that studied the efficacy of laxatives, naloxone, and naloxegol in treating OIC. Newer strategies addressing the causal pathophysiology of OIC are needed for a more effective assessment and management of OIC. Finally, traditional recommended therapies are appraised and compared with the latest pharmacological developments. Future research should address whether naloxegol is more efficacious by its comparison directly with first-line treatments, including laxatives.

Using buprenorphine to treat patients with opioid use disorder

The US opioid epidemic is a complex problem that has resulted in legislative actions to make treatment more accessible to patients. Physician assistants (PAs) have taken an active role in expanding their scope of practice to keep up with treatment needs. This article describes opioid use disorder in the United States, treatment gaps, safe treatment with buprenorphine, and PA prescriptive authority.

The Mechanisms Involved in Morphine Addiction: An Overview

Opioid use disorder is classified as a chronic recurrent disease of the central nervous system (CNS) which leads to personality disorders, co-morbidities and premature death. It develops as a result of long-term administration of various abused substances, along with morphine. The pharmacological action of morphine is associated with its stimulation of opioid receptors. Opioid receptors are a group of G protein-coupled receptors and activation of these receptors by ligands induces significant molecular changes inside the cell, such as an inhibition of adenylate cyclase activity, activation of potassium channels and reductions of calcium conductance. Recent data indicate that other signalling pathways also may be involved in morphine activity. Among these are phospholipase C, mitogen-activated kinases (MAP kinases) or β-arrestin. The present review focuses on major mechanisms which currently are considered as essential in morphine activity and dependence and may be important for further studies.

Pain and distress management in palliative neonatal care

Palliative care concentrates on preventing and relieving suffering by reducing the severity of disease symptoms. Consistent treatment of pain and distress must therefore be an integral component of every palliative care concept. In this review non-pharmacological and pharmacological measures for pain and distress management in the context of palliative neonatal care are summarised. Furthermore, recommendations are given focusing on two special palliative neonatal care settings: compassionate extubation and withdrawing artificial nutrition and hydration.

Efficacy of pharmacological therapies for the treatment of opioid-induced constipation: systematic review and network meta-analysis

OBJECTIVE

Opioids are increasingly prescribed in the West and have deleterious GI consequences. Pharmacological therapies to treat opioid-induced constipation (OIC) are available, but their relative efficacy is unclear. We performed a systematic review and network meta-analysis to address this deficit in current knowledge.

DESIGN

We searched MEDLINE, EMBASE, EMBASE Classic and the Cochrane central register of controlled trials through to December 2017 to identify randomised controlled trials (RCTs) of pharmacological therapies in the treatment of adults with OIC. Trials had to report a dichotomous assessment of overall response to therapy, and data were pooled using a random effects model. Efficacy and safety of pharmacological therapies was reported as a pooled relative risk (RR) with 95% CIs to summarise the effect of each comparison tested and ranked treatments according to their P-score.

RESULTS

Twenty-seven eligible RCTs of pharmacological therapies, containing 9149 patients, were identified. In our primary analysis, using failure to achieve an average of ≥3 bowel movements (BMs) per week with an increase of ≥1 BM per week over baseline or an average of ≥3 BMs per week, to define non-response, the network meta-analysis ranked naloxone first in terms of efficacy (RR=0.65; 95% CI 0.52 to 0.80, P-score=0.84), and it was also the safest drug. When non-response to therapy was defined using failure to achieve an average of ≥3 BMs per week, with an increase of ≥1 BM per week over baseline, naldemedinewas ranked first (RR=0.66; 95% CI 0.56 to 0.77, P score=0.91) and alvimopan second (RR=0.74; 95% CI 0.57 to 0.94, P-score=0.71).

CONCLUSION

In network meta-analysis, naloxone and naldemedine appear to be the most efficacious treatments for OIC. Naloxone was the safest of these agents.

Simultaneous quantification of high-dose naloxone and naloxone-3-β-d-glucuronide in human plasma by UHPLC-MS/MS

Aim: High-dose administration of the μ-opioid receptor inverse agonist naloxone (NX), has previously been demonstrated to reinstate nocifensive behavior in the late phase of inflammatory injuries. However, no current analytical methods can provide pharmacokinetic insight into the pharmacodynamic response of high-dose administration of NX. Materials & methods: Based on protein precipitation using 50 μl human plasma, NX and naloxone-β-d-glucuronide (NXG) was analysed by UHPLC-MS/MS with 6 min cycle time. Results: A method for quantification of high-dose administered NX and NXG was developed and validated with intra- and interday precision and accuracy within ≤8.5% relative standard deviation (RSD) and -1.2-5.5% relative error (RE) for NX and ≤9.6% RSD and 0.6-6.5% RE for NXG. The method show excellent internal standard corrected matrix effects. Conclusion: A rapid UHPLC-MS/MS method was developed for quantification of NX and NXG in human plasma within 10-4000 ng/ml.

Pathophysiology and management of opioid-induced constipation: European expert consensus statement

Background

Opioid-induced bowel dysfunction is a complication of opioid therapy, in which constipation is the most common and problematic symptom. However, it is frequently under-recognised and thus effective management is often not instituted despite a number of treatment options.

Objective

The central objective of this study is to provide a summary of the pathophysiology and clinical evaluation of opioid-induced constipation and to provide a pragmatic management algorithm for day-to-day clinical practice.

Methods

This summary and the treatment algorithm is based on the opinion of a European expert panel evaluating current evidence in the literature.

Results

The pathophysiology of opioid-induced constipation is multi-faceted. The key aspect of managing opioid-induced constipation is early recognition. Specific management includes increasing fluid intake, exercise and standard laxatives as well as addressing exacerbating factors. The Bowel Function Index is a useful way of objectively evaluating severity of opioid-induced constipation and monitoring response. Second-line treatments can be considered in those with recalcitrant symptoms, which include gut-restricted or peripherally acting mu-opioid receptor antagonists. However, a combination of interventions may be needed.

Conclusion

Opioid-induced constipation is a common, yet under-recognised and undertreated, complication of opioid therapy. We provide a pragmatic step-wise approach to opioid-induced constipation, which should simplify management for clinicians.

Low-Dose Versus High-Dose Postoperative Naloxone Infusion Combined With Patient-Controlled Analgesia for Adolescent Idiopathic Scoliosis Surgery: A Randomized Controlled Trial

STUDY DESIGN

Randomized controlled trial.

OBJECTIVES

The aim of this prospective randomized clinical trial was to compare low (0.5 μg/kg/h) and high (2.5 μg/kg/h) dose naloxone infusion on the time to tolerate liquids and meals after surgery, patient-controlled analgesia (PCA) opioid requirements, nausea and pruritus ratings, and hospital length of stay.

SUMMARY OF BACKGROUND DATA

Adolescents undergoing posterior spinal fusion often receive PCA after surgery and may experience common opioid-associated side effects, including nausea and pruritus. Low-dose naloxone infusion has been shown to reduce the incidence of pruritus and nausea while preserving analgesia, although an ideal dose has not been determined. Less is known about the potential for naloxone to improve bowel function after surgery.

METHODS

Eighty-four patients (age 10-21 years) were randomly allocated to receive low- or high-dose naloxone infusion postoperatively. Surgical anesthetic consisted of propofol and opioid infusion with intrathecal morphine (10-15 μg/kg) at the conclusion of surgery. A visual analog scale (VAS) was used to rate nausea and pruritus.

RESULTS

The groups had similar time to oral liquid intake after surgery and transition from PCA to oral pain medication. The VAS scores for pruritus and nausea were also similar, as was the need to treat these side effects. Morphine equivalents were similar between groups on postoperative day (POD) 0 and 1. On POD 2, the high-dose infusion group had significantly greater PCA bolus use (1.41±0.9 vs. 1.04±0.6; p<.05), although pain scores did not differ significantly. Hospital length of stay was similar for the two groups.

CONCLUSION

High-dose naloxone infusion was associated with similar rates of opioid side effects as low-dose. Increased PCA use noted on POD 2 may represent partial reversal of opioid analgesia in the high-dose naloxone group.

LEVEL OF EVIDENCE

Level 1.

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.

Pharmacological Treatment of Opioid-Induced Constipation Is Effective but Choice of Endpoints Affects the Therapeutic Gain

BACKGROUND

Widespread opioid use has led to increase in opioid-related adverse effects like constipation. We examined the impact of study endpoints on reported treatment benefits.

METHODS

Using MEDLINE, EMBASE, and ClinicalTrials.gov, we searched for randomized control trials targeting chronic opioid-induced constipation (OIC) and subjected them to meta-analysis. Data are given with 95% confidence intervals.

RESULTS

Thirty trials met our inclusion criteria. Combining all dichotomous definitions of responders, active drugs were consistently more effective than placebo, with an odds ratio (OR): 2.30 [2.01-2.63; 15 studies], independent of the underlying drug mechanism. The choice of endpoints significantly affected the therapeutic gain. When time from drug administration to defecation was used, the OR decreased from 4.74 [2.71-4.74] at 6 h or less to 2.46 [1.80-3.30] at 24 h (P < 0.05). Using other response definitions, the relative benefit over placebo was 2.10 [1.77-2.50; 12 studies] for weekly bowel frequency, 2.03 [1.39-2.95; 9 studies] for symptom scores, 2.21 [1.25-3.90; 4 studies] for global assessment scales, and 1.27 [0.79-2.03; 7 studies] for rescue laxative use.

CONCLUSION

While treatment of OIC with active drugs is more effective than placebo, the relative gain depends on the choice of endpoints. The commonly used time-dependent response definition is associated with the highest response rate but is of questionable relevance in a chronic disorder. The limited data do not clearly demonstrate a unique advantage of the peripherally restricted opioid antagonists, suggesting that treatment with often cheaper agents should be optimized before shifting to these novel expensive agents.

Peripherally Acting μ-Opioid Receptor Antagonists for the Treatment of Opioid-Related Side Effects: Mechanism of Action and Clinical Implications

Opioid receptors are distributed throughout the central and peripheral nervous systems and on many nonneuronal cells. Therefore, opioid administration induces effects beyond analgesia. In the enteric nervous system (ENS), stimulation of µ-opioid receptors triggers several inhibitory responses that can culminate in opioid-induced bowel dysfunction (OBD) and its most common side effect, opioid-induced constipation (OIC). OIC negatively affects patients' quality of life (QOL), ability to work, and pain management. Although laxatives are a common first-line OIC therapy, most have limited efficacy and do not directly antagonize opioid effects on the ENS. Peripherally acting µ-opioid receptor antagonists (PAMORAs) with limited ability to cross the blood-brain barrier have been developed. The PAMORAs approved by the U S Food and Drug Administration for OIC are subcutaneous and oral methylnaltrexone, oral naloxegol, and oral naldemedine. Although questions of cost-effectiveness and relative efficacy versus laxatives remain, PAMORAs can mitigate OIC and improve patient QOL. PAMORAS may also have applications beyond OIC, including reducing the increased cardiac risk or potential tumorigenic effects of opioids. This review discusses the burden of OIC and OBD, reviews the mechanism of action of new OIC therapies, and highlights other potential opioid-related side effects mediated by peripheral opioid receptors in the context of new OIC therapies.

Efficacy of Treatments for Opioid-Induced Constipation: Systematic Review and Meta-analysis

BACKGROUND & AIMS

Opioid-induced constipation (OIC) is a common problem in patients on chronic opioid therapy for cancer-related and non-cancer-related pain. Approved treatments for OIC are methylnaltrexone, naloxone, naloxegol, alvimopan, naldemedine, and lubiprostone. Since a meta-analysis performed in 2014, 2 new agents have been approved by the Food and Drug Administration for treatment of OIC (naloxegol and naldemedine).

METHODS

We conducted a search of the medical literature following the protocol outlined in the Cochrane Handbook for systematic review. We searched MEDLINE, EMBASE, EMBASE Classic, Web of Science, and the Cochrane Central Register of Controlled Trials until March 2017 to identify randomized controlled trials of peripheral μ-opioid-receptor antagonists (methylnaltrexone, naloxone, naloxegol, alvimopan, axelopran, or naldemedine), lubiprostone, or prucalopride. Response to therapy was extracted in a dichotomous assessment as an overall response to therapy. The effect of pharmacologic therapies was pooled and reported as a relative risk (RR) of failure to respond to the treatment drug, with 95% CIs.

RESULTS

We included 27 placebo-controlled trials in our meta-analysis (23 trials evaluated μ-opioid-receptor antagonists, 3 trials evaluated lubiprostone, and 1 trial evaluated prucalopride). In these trials, 5390 patients received a drug and 3491 received a placebo. Overall, μ-opioid-receptor antagonists, lubiprostone, and prucalopride were superior to placebo for the treatment of OIC, with a RR of failure to respond to therapy of 0.70 (95% CI, 0.64-0.75) and an overall number needed to treat of 5 (95% CI, 4-7). When restricted to only Food and Drug Administration-approved medications for OIC, the RR of failure to respond to therapy was 0.69 (95% CI, 0.62-0.77), with a number needed to treat of 5 (95% CI, 4-7). Sensitivity analyses and meta-regression performed to account for heterogeneity showed that treatment was more likely to be effective in study populations taking higher doses of opiates at baseline or refractory to laxatives. Study duration and prespecified primary outcome did not affect the RR of failure. Participants who received μ-opioid-receptor antagonists were significantly more likely to have diarrhea, abdominal pain, nausea, or vomiting than patients who received placebo.

CONCLUSIONS

In a systematic review and meta-analysis, we found μ-opioid-receptor antagonists to be safe and effective for the treatment of OIC. Prescription-strength laxatives (prucalopride, lubiprostone) are slightly better than placebo in reducing OIC.

New developments in the treatment of opioid-induced gastrointestinal symptoms

Chronic pain affects a large part of the global population, leading to an increase of opioid use. Opioid-induced constipation (OIC), a highly prevalent adverse effect of opioid use, has a major impact on patients' quality of life. Thanks to the introduction of new drugs for chronic constipation, which can also be used in OIC, and the development of peripherally acting mu-opioid receptor blockers, specifically for use in OIC, therapeutic options have seen major development. This review summarises current and emerging treatment options for OIC based on an extensive bibliographical search. Efficacy data for laxatives, lubiprostone, prucalopride, linaclotide, oxycodone/naloxone combinations, methylnaltrexone, alvimopan, naloxegol, naldemedine, axelopran, and bevenopran in OIC are summarised.

The Efficacy of Peripheral Opioid Antagonists in Opioid-Induced Constipation and Postoperative Ileus: A Systematic Review of the Literature

Opioid-induced constipation has a negative impact on quality of life for patients with chronic pain and can affect more than a third of patients. A related but separate entity is postoperative ileus, which is an abnormal pattern of gastrointestinal motility after surgery. Nonselective μ-opioid receptor antagonists reverse constipation and opioid-induced ileus but cross the blood-brain barrier and may reverse analgesia. Peripherally acting μ-opioid receptor antagonists target the μ-opioid receptor without reversing analgesia. Three such agents are US Food and Drug Administration approved. We reviewed the literature for randomized controlled trials that studied the efficacy of alvimopan, methylnaltrexone, and naloxegol in treating either opioid-induced constipation or postoperative ileus. Peripherally acting μ-opioid receptor antagonists may be effective in treating both opioid-induced bowel dysfunction and postoperative ileus, but definitive conclusions are not possible because of study inconsistency and the relatively low quality of evidence. Comparisons of agents are difficult because of heterogeneous end points and no head-to-head studies.

Reduction in pain: Is it worth the gain? The effect of opioids on the GI tract

The use of opioid medications for acute and chronic pain has increased significantly in the past 20 years in the United States. Given the high density of opioid receptors in the gastrointestinal tract, side effects are common in these patients including constipation, dysphagia, bloating, nausea, and vomiting. These side effects, which are experienced by most patients who take opioids, can lead to significant impairment in quality of life. Unlike other side effects from opioids, gastrointestinal side effects do not diminish with continued use, often leading patients to reduce or discontinue their opioid treatment to relieve these side effects. Therefore, physicians must be aware and anticipate potential side effects in patients receiving opioids to ensure appropriate pain management.

Drugs for Treating Opioid-Induced Constipation: A Mixed Treatment Comparison Network Meta-analysis of Randomized Controlled Clinical Trials

CONTEXT

Opioid-induced constipation is a common problem associated with chronic use of opioid analgesics.

OBJECTIVES

The objective of this study was to compare available interventions for the treatment of opioid-induced constipation, using principles of network meta-analysis.

METHODS

Electronic databases were searched for randomized controlled clinical trials evaluating drugs used in opioid-induced constipation. Number of patients with rescue-free bowel movements (RFBM) was the primary outcome, and time for achieving RFBM, adverse events, and changes in the analgesic activity of the opioid analgesics were the secondary outcomes. Inverse variance heterogeneity model was used for direct and mixed treatment comparison analysis. Odds ratio for categorical outcomes and weighted mean difference for numerical outcomes were the effect estimates.

RESULTS

We included a total of 23 studies in the systematic review and 21 in the network meta-analysis. Lubriprostone, prucalopride, naldemedine, naloxegol, alvimopan, subcutaneous, and oral methyl naltrexone were observed to perform better than placebo in terms of RFBM. Additionally, subcutaneous methyl naltrexone was significantly better than lubiprostone, naloxegol, oral methyl naltrexone, and prucalopride. Lubiprostone and naldemedine were associated with increased risks of adverse events. Subcutaneous methyl naltrexone did not significantly affect the analgesia due to background opioid use. Quality of evidence for the comparisons is either low or very low.

CONCLUSION

Subcutaneous methyl naltrexone was found to perform better than other interventions for managing opioid-induced constipation.

Treatment with Naloxegol Versus Placebo: Pain Assessment in Patients with Noncancer Pain and Opioid-Induced Constipation

OBJECTIVE

To summarize results from pain and opioid use assessments with naloxegol in adults with opioid-induced constipation (OIC) and chronic noncancer pain.

METHODS

Two phase 3 randomized, double-blind, 12-week studies evaluated the efficacy and safety of oral naloxegol (12.5 or 25 mg daily) in adults (18 to < 85 years) with confirmed OIC and chronic noncancer pain: KODIAC-04 (NCT01309841) and KODIAC-05 (NCT01323790). Pain level was assessed daily (11-point numeric rating scale [NRS]; 0 = no pain, 10 = worst imaginable pain). Changes from baseline in mean weekly pain scores and opioid dose (weeks 1 through 12) were analyzed using mixed-model repeated measures.

RESULTS

At baseline, mean daily NRS average pain scores ranged from 4.5 to 4.8 for all groups in KODIAC-04 (N = 652) and were 4.6 for each group in KODIAC-05 (N = 700). Respective mean ± SD changes from baseline average pain for placebo, naloxegol 12.5 mg, and naloxegol 25 mg were -0.2 ± 1.07, -0.3 ± 1.05 (P = 0.773 vs. placebo), and 0.2 ± 0.95 (P = 0.837 vs. placebo; KODIAC-04) and -0.1 ± 0.94, -0.1 ± 0.87 (P = 0.744), and 0.0 ± 1.18 (P = 0.572; KODIAC-05). At baseline, mean daily opioid doses ranged from 135.6 to 143.2 morphine equivalent units (MEUs)/day in KODIAC-04, and from 119.9 to 151.7 MEUs/day in KODIAC-05. Respective mean ± SD changes from baseline dose were -1.8 ± 30.19, -2.3 ± 20.52 (P = 0.724 vs. placebo), and 0.4 ± 13.01 (P = 0.188 vs. placebo; KODIAC-04) and -0.3 ± 17.14, -1.3 ± 17.11 (P = 0.669 vs. placebo), and 0.1 ± 8.54 (P = 0.863 vs. placebo; KODIAC-05). Changes in maintenance opioid dose were few; reasons for such changes were similar across treatment groups.

CONCLUSION

Centrally mediated opioid analgesia was maintained during treatment with naloxegol in patients with noncancer pain and OIC.

Opioid-Induced Constipation Relief From Fixed-Ratio Combination Prolonged-Release Oxycodone/Naloxone Compared With Oxycodone and Morphine for Chronic Nonmalignant Pain: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

CONTEXT

Opioid-induced constipation (OIC) is one of the most frequent and severe adverse events (AEs) after treatment with opioids. Recent studies have indicated that fixed-ratio combination prolonged-release oxycodone/naloxone (OXN PR) could decrease OIC with similar pain relief compared with other opioids.

OBJECTIVES

We systematically reviewed (PROSPERO registration numbers: CRD42016036244) the constipation relief of OXN PR compared with other opioids regardless of formulation, prolonged release, or extended release used for the relief of chronic pain.

METHODS

Relevant studies were identified by searching PubMed, EMBASE, Web of Science, and the Cochrane library from inception to May 2016, with an update to December 2016. We quantitatively analyzed OIC (assessed by bowel function index [BFI]), pain intensity, and AEs.

RESULTS

A total of 167 articles were identified from the databases. Finally seven studies with 3217 patients were included in our meta-analysis, including 1322 patients in OXN PR treatment groups and 1885 patients in prolonged-release oxycodone (OXY PR) or prolonged-release morphine (MOR PR) control group. The relative risk (RR) of OIC was decreased in OXN PR (RR 0.52, 95% CI 0.44; 0.62). Whether BFI was better or worse at baseline, the mean difference (MD) of BFI -17.48 95% CI -21.60; -13.36) was better after treatment with OXN PR with clinical importance at the end of intervention; moreover, the BFI of the OXN PR-treated group was closer to normal BFI scores. However, clinical BFI change from baseline to the end measurement only existed in patients when the baseline BFI was high (mean [SDs] 61.0 [23.39]-67.40 [19.51]), and the MD of the BFI was -15.96 (95% CI -25.56; -15.48). The RR of AEs was also smaller (RR 0.80; 95% CI 0.69-0.93), but the severity or duration of AEs was not reported. Pain intensity was also significantly decreased in the OXN PR treatment groups (MD -3.84, 95% CI -7.14; -0.55), although there was no clinically meaningful difference.

CONCLUSION

For people with chronic pain, treatment with OXN PR decreases the incidence of OIC and provides intermediate-term bowel function improvement with clinical importance; in addition, pain relief is not weakened. The OIC after treatment with OXN PR for cancer-related pain and over the long term remains unknown.

The Efficacy and Safety of Transcutaneous Acupoint Interferential Current Stimulation for Cancer Pain Patients With Opioid-Induced Constipation: A Prospective Randomized Controlled Study

Introduction. Opioid-induced constipation (OIC) is a principal complication secondary to analgesic therapy for cancer pain patients who suffer moderate to severe pain. In this study, we observe the efficacy and safety of transcutaneous acupoint interferential current (IFC) stimulation in those patients with OIC. Methods. A total of 198 patients were randomly allocated to the IFC group and control group in a 1:1 ratio. Finally, 98 patients in the IFC group received 14 sessions administered over 2 weeks, whereas 100 patients in the control group took lactulose orally during the same period. Observation items were documented at management stage and at follow-up stage according to Cleveland Constipation Scales (CCS), pain Numeric Rating Scales (NRS) and Patient Assessment of Constipation Quality of Life (PAC-QoL). Results. The total curative effects of the IFC group and the control group were indistinguishable (76.5% vs 70.0%, P = .299). Regarding CCS and PAC-QoL scores, no significant difference was observed between the 2 groups during the management time and at the follow-up stage of week 3 (P > .05, respectively), but groups were distinguished at the follow-up stage of week 4 (P < .001 and P = .031, respectively). The pain NRS decreased significantly at management stage week 2 and follow-up stage week 3 and week 4 (P = .013, P = .041, P = .011, respectively). Conclusions. Transcutaneous acupoint IFC therapy over acupoints of Tianshu (ST25) and Zhongwan (RN12) may improve constipation and quality of life in cancer patients receiving opiates; further studies are worthwhile.

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.

Opioids in Gastroenterology: Treating Adverse Effects and Creating Therapeutic Benefits

The use of opioid medications on both an acute and chronic basis is ubiquitous in the United States. As opioid receptors densely populate the gastrointestinal tract, symptoms and side effects can be expected in these patients. In the esophagus, dysmotility may result, manifesting with dysphagia and a syndrome indistinguishable from primary achalasia. In the stomach, a marked delay in gastric emptying may occur with postprandial nausea and early satiety. Postoperatively, particularly with abdominal surgery, opioid-induced ileus may ensue. In the colon, opioid-induced constipation is common. A unique syndrome termed narcotic bowel syndrome is characterized by chronic abdominal pain often accompanied by nausea and vomiting in the absence of other identifiable causes. With the recognition of the important role of opioids on gastrointestinal function, novel drugs have been developed that use this physiology. These medications include peripheral acting opioid agonists to treat opioid-induced constipation and combination agonist and antagonists used for diarrhea-predominant irritable bowel syndrome. This review summarizes the most recent data in these areas.

Pharmacologic Profile of Naloxegol, a Peripherally Acting µ-Opioid Receptor Antagonist, for the Treatment of Opioid-Induced Constipation

Opioid-induced constipation (OIC) is a common side effect of opioid pharmacotherapy for the management of pain because opioid agonists bind to µ-opioid receptors in the enteric nervous system (ENS). Naloxegol, a polyethylene glycol derivative of naloxol, which is a derivative of naloxone and a peripherally acting µ-opioid receptor antagonist, targets the physiologic mechanisms that cause OIC. Pharmacologic measures of opioid activity and pharmacokinetic measures of central nervous system (CNS) penetration were employed to characterize the mechanism of action of naloxegol. At the human µ-opioid receptor in vitro, naloxegol was a potent inhibitor of binding (K_i = 7.42 nM) and a neutral competitive antagonist (pA₂ - 7.95); agonist effects were <10% up to 30 μM and identical to those of naloxone. The oral doses achieving 50% of the maximal effect in the rat for antagonism of morphine-induced inhibition of gastrointestinal transit and morphine-induced antinociception in the hot plate assay were 23.1 and 55.4 mg/kg for naloxegol and 0.69 and 1.14 mg/kg by for naloxone, respectively. In the human colon adenocarcinoma cell transport assay, naloxegol was a substrate for the P-glycoprotein transporter, with low apparent permeability in the apical to basolateral direction, and penetrated the CNS 15-fold slower than naloxone in a rat brain perfusion model. Naloxegol-derived radioactivity was poorly distributed throughout the rat CNS and was eliminated from most tissues within 24 hours. These findings corroborate phase 3 clinical studies demonstrating that naloxegol relieves OIC-associated symptoms in patients with chronic noncancer pain by antagonizing the µ-opioid receptor in the ENS while preserving CNS-mediated analgesia.

Nanoconjugated NAP as a Potent and Periphery Selective Mu Opioid Receptor Modulator To Treat Opioid-Induced Constipation

Opioids are the mainstay for cancer and noncancer pain management. However, their use is often associated with multiple adverse effects. Among them, the most common and persistent one is probably opioid-induced constipation (OIC). Periphery selective opioid antagonists may alleviate the symptoms of OIC without compromising the analgesic effects of opioids. Recently our laboratories have identified one novel lead compound, 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-[(4'-pyridyl)acetamido]morphinan (NAP), as a peripherally selective mu opioid receptor ligand carrying subnanomolar affinity to the mu opioid receptor and over 100-folds of selectivity over both the delta and kappa opioid receptors, with reasonable oral availability and half-life, and potential to treat OIC. Nanoparticle-based drug delivery systems are now widely considered due to their technological advantages such as good stability, high carrier capacity, low therapeutic side effects, etc. Herein we report nanoparticle supported NAP as a potential candidate for OIC treatment with improved peripheral selectivity over the original lead compound NAP.