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

Systemic morphine administration causes gastric distention and hyperphagia in healthy horses

BACKGROUND

There are no data investigating the effect of systemic morphine on the size of the stomach or the food consumption in horses.

OBJECTIVES

To evaluate gastrointestinal side effects of morphine administered systemically in healthy horses by the means of clinical and ultrasonographic evaluations.

STUDY DESIGN

In vivo experiment.

METHODS

On day 1 of the experiment, six healthy French Trotter mares were evaluated clinically and an abdominal ultrasonography was performed three times 4 h apart to record the size of the stomach, the number of contractions per minute of the duodenum, jejunum, caecum, left and right ventral colons. On Day 2, morphine was administered three times 4 h apart at the dose of 0.1 mg/kg i.v. and the same ultrasonographic examinations performed. On Day 3, only clinical and ultrasonographic examinations were performed as on Day 1. Amounts of hay and water ingested, frequency and weight of faeces were recorded throughout the study.

RESULTS

Number of contractions of the duodenum, caecum, left and right ventral colons were significantly decreased after morphine administration. Size of the stomach was increased significantly with a cumulative effect of repeated doses of morphine. Hay (+0.4 kg/h, P<0.001) and water (+1.1 L/h, P<0.001) consumption were significantly increased.

MAIN LIMITATIONS

The study was performed in healthy horses.

CONCLUSIONS

Systemic morphine administration causes gastrointestinal depression, gastric distention and hyperphagia in horses. Clinical and ultrasonographical examinations are valuable tools to identify side effects of morphine administration in horses. Further studies are needed to assess side effects and monitoring in clinically painful cases. Horses receiving systemic morphine administration should be closely monitored for signs of gastric distention and, specifically, the amount of food given while receiving treatment should be controlled to avoid complications.

Prucalopride for the treatment of constipation: a view from 2015 and beyond

Prucalopride is a prokinetic drug, that has been commercially available in recent years for the treatment of chronically constipated patients. In this update of a previous 2016 article, we reviewed the more recent data supporting its role in the treatment of constipation and constipation-associated conditions. Areas covered: We carried out an extensive literature review on the effects of prucalopride for the years 2012-2018 by means of scientific databases and manual research. More evidence was found on its possible therapeutic role in conditions in which constipation plays a role as an associated symptom, such as opioid-induced constipation, constipation-predominant irritable bowel syndrome, post-operative ileus, colonic diverticular disease, drug-related constipation, and chronic intestinal pseudo-obstruction. Expert opinion: Based on the added literature evidence, we feel that prucalopride is an effective, although expensive, drug for the treatment of primary and secondary forms of constipation, and of other clinical conditions associated with constipation.

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.

Methylnaltrexone: Peripherally Acting µ-Opioid Receptor Antagonist

Opioid-induced constipation (OIC) is a common adverse effect associated with opioid therapy, with many patients never developing tolerance to this effect. There are many traditional laxatives available to help patients combat this symptom, yet OIC may not reliably respond to conventional treatment. Peripherally acting µ-opioid receptor antagonists (PAMORAs) have a place in the treatment of refractory OIC, when traditional laxatives have not resulted in effective laxation. There are a number of PAMORAs now available, and methylnaltrexone is the only PAMORA indicated for the treatment of OIC in adults with advanced illness, as well as for patients with chronic noncancer pain, including patients with chronic pain related to prior cancer treatment who do not require frequent opioid escalation. Advanced practitioners need to have an understanding of how and when to best use these medications for the different indications in patients with advanced illness or chronic noncancer-related pain.

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.

The gut microbiota mediates reward and sensory responses associated with regimen-selective morphine dependence

Opioid use for long-term pain management is limited by adverse side effects, such as hyperalgesia and negative affect. Neuroinflammation in the brain and spinal cord is a contributing factor to the development of symptoms associated with chronic opioid use. Recent studies have described a link between neuroinflammation and behavior that is mediated by a gut-brain signaling axis, where alterations in indigenous gut bacteria contribute to several inflammation-related psychopathologies. As opioid receptors are highly expressed within the digestive tract and opioids influence gut motility, we hypothesized that systemic opioid treatment will impact the composition of the gut microbiota. Here, we explored how opioid treatments, and cessation, impacts the mouse gut microbiome and whether opioid-induced changes in the gut microbiota influences inflammation-driven hyperalgesia and impaired reward behavior. Male C57Bl6/J mice were treated with either intermittent or sustained morphine. Using 16S rDNA sequencing, we describe changes in gut microbiota composition following different morphine regimens. Manipulation of the gut microbiome was used to assess the causal relationship between the gut microbiome and opioid-dependent behaviors. Intermittent, but not sustained, morphine treatment was associated with microglial activation, hyperalgesia, and impaired reward response. Depletion of the gut microbiota via antibiotic treatment surprisingly recapitulated neuroinflammation and sequelae, including reduced opioid analgesic potency and impaired cocaine reward following intermittent morphine treatment. Colonization of antibiotic-treated mice with a control microbiota restored microglial activation state and behaviors. Our findings suggest that differing opioid regimens uniquely influence the gut microbiome that is causally related to behaviors associated with opioid dependence.

A Retrospective Study of Patients Undergoing Radical Cystectomy and Receiving Peri-Operative Naloxegol or Alvimopan: Comparison of Length of Stay

Alvimopan is a μ-opioid receptor antagonist used in the post-operative period to decrease rates of post-operative ileus (POI) following radical cystectomy (RC) and thereby shorten length of stay (LOS). Naloxegol is a much less expensive drug of the same class that has yet to be studied for prevention of POI in the peri-operative period. The purpose of the current study is to evaluate the differences in LOS and development of POI in patients post-RC who take alvimopan versus those who take naloxegol, with the hope that drug efficacy can be evaluated against the significant difference in cost burden between the two drugs. The study population included all adult patients between 18-89 years of age with bladder cancer undergoing radical cystectomy with urostomy at University of Colorado Hospital. Those patients who received usual post-operative care as well as either alvimopan or naloxegol between September 2011 and December 2017 were selected for analysis. Patients who did not take either medication or were switched from one drug to the other were excluded from the study. A zero-truncated binomial regression analysis was used to analyze differences in length of stay in patients who received alvimopan versus those who received naloxegol. Additionally, the incidence of post-operative ileus was compared between treatment groups. 130 patients who underwent RC and received either alvimopan or naloxegol were included in the study: 75 (58%) received alvimopan and 55 (42%) received naloxegol. Baseline characteristics were similar between treatment groups. There was no significant difference in the length of stay between patients who received alvimopan and patients who received naloxegol after adjusting for age, sex, BMI, length of surgical time, or stage of disease (p = 0.41). There was no significant between the two drugs for development of POI (p = 0.85). Development of POI was significantly associated with a longer LOS (p = 0.007). The analysis showed that naloxegol was comparable to alvimopan when it came to length of hospital stay following RC. Therefore, naloxegol may be offered as a less expensive, effective alternative to alvimopan.