ADL 8-2698, a trans-3,4-dimethyl-4-(3-hydroxyphenyl) piperidine, prevents gastrointestinal effects of intravenous morphine without affecting analgesia

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

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

Alvimopan for the reduction of postoperative ileus after long posterior spinal fusion: placebo-controlled double-blind randomized trial

OBJECTIVE

The aim of this study was to evaluate the efficacy of alvimopan administration after posterior spinal fusion (PSF) in adult spine surgery patients who are taking opioid agents.

METHODS

In this placebo-controlled, double-blind randomized trial, PSF patients were randomized in blocks to placebo or study drug. Primary and secondary outcome measures were return to normal bowel function, including time to passage of flatus and stool, time to tolerance of oral nutrition, and time to hospital discharge. Patients were included regardless of chronic opioid consumption status.

RESULTS

Thirty-one patients provided consent for participation, and 26 patients (13 per group) completed the study. There were no differences between groups with respect to time to flatus, time to bowel movement, time to oral nutrition tolerance, and time to discharge. Calculated effect sizes favored placebo for all interventions.

CONCLUSIONS

Alvimopan did not hasten return to bowel function for any primary or secondary outcome measures when compared with placebo for patients undergoing PSF. There were no adverse events related to alvimopan, including for patients with chronic opioid consumption. While underpowered to determine a statistical difference, it is unlikely that a clinically relevant effect exists.

Stereoselective HPLC separation of alvimopan on cellulose-based immobilized polysaccharide as a chiral stationary phase

Chiral separation by normal phase high performance liquid chromatography is one of the most powerful technique to quantify the chiral purity of the compounds. In this study, a novel, simple, and specific analytical method was proposed to ascertain the chiral purity of alvimopan (ALV). The normal phase HPLC method was developed based on cellulose tris (3,5-dichlorophenylcarbamate) stationary phase. The separation of ALV isomers achieved by using column CHIRALPAK IC (250 × 4.6 mm, 5 μm), mobile phase n-hexane: isopropyl alcohol: ethanol: diethylamine (650:200:150:5 v/v), column oven temperature 30°C, flow rate 1.0 mL min-1 , injection volume was 10 μL, chromatographic response monitored at 273 nm. The developed method was validated as per the ICH guidelines and found precise, accurate, and linear. The advantage of the method is a good separation of ALV isomers within 35 minutes of the analysis time. Therefore, this method is suitable for routine determination of chiral purity of ALV active pharmaceutical ingredient.

Cost and efficacy examination of alvimopan for the prevention of postoperative ileus

Opioid analgesics exacerbate ileus through peripheral μ-opioid receptor action. Alvimopan, a μ-opioid receptor antagonist, has been proposed to alleviate postoperative ileus, leading to decreased time to return of gastrointestinal function and hospital discharge. As opioid-induced motility issues are only one factor affecting postoperative ileus, continued examination of the cost of the use and efficacy of the drug is needed. Data for this study were collected retrospectively from the charts of 55 patients who received an anastomosis and were given alvimopan at Morristown Medical Center between 2010 and 2013 as well as from 58 appropriately matched controls. The billing record and chart for each patient was examined, and information on total hospital charges, age, sex, body mas index, primary diagnosis, procedure type, length of stay (days), time to return of bowel function (hours), and outcomes were recorded for analysis. No difference between patients given alvimopan and controls was observed for the length of hospital stay (4.6 vs 4.8 days) or for time to return of bowel function (68.5 vs 67.3 hours). Total hospital charges were higher for treated patients (p=0.0080), averaging $48 705.15 and $41 068.80, respectively. Alvimopan was not associated with improved clinical outcome but was associated with an increase in hospital charges within this population.

Germanium-on-silicon mid-infrared grating couplers with low-reflectivity inverse taper excitation

A broad transparency range of its constituent materials and compatibility with standard fabrication processes make germanium-on-silicon (Ge-on-Si) an excellent platform for the realization of mid-infrared photonic circuits. However, the comparatively large Ge waveguide thickness and its moderate refractive index contrast with the Si substrate hinder the implementation of efficient fiber-chip grating couplers. We report for the first time, to the best of our knowledge, a single-etch Ge-on-Si grating coupler with an inversely tapered access stage, operating at a 3.8 μm wavelength. Optimized grating excitation yields a coupling efficiency of -11  dB (7.9%), the highest value reported for a mid-infrared Ge-on-Si grating coupler, with reflectivity below -15  dB (3.2%). The large periodicity of our higher-order grating design substantially relaxes the fabrication constraints. We also demonstrate that a focusing geometry allows a 10-fold reduction in inverse taper length, from 500 to 50 μm.

The use of alvimopan for postoperative ileus in small and large bowel resections

Transient ileus is a normal physiologic process after surgery. When prolonged, it is an important contributor to postoperative complications, increased length of stay and increased healthcare costs. Efforts have been made to prevent and manage postoperative ileus; alvimopan is an oral, peripheral μ-opioid receptor antagonist, and the only currently US FDA-approved medication to accelerate the return of gastrointestinal function postoperatively.

Is there value in alvimopan in minimally invasive colorectal surgery?

BACKGROUND

Alvimopan's goal is to minimize postoperative ileus and optimize outcomes; however, evidence in laparoscopic surgery is lacking. Our goal was to evaluate the benefit of alvimopan in laparoscopic colorectal surgery with an enhanced recovery pathway (ERP).

METHODS

Laparoscopic colorectal cases were stratified into alvimopan and control cohorts, then case-matched for comparability. All followed an identical ERP. The main outcomes were length of stay, complications, readmissions, and costs in the alvimopan and control groups.

RESULTS

About 321 patients were analyzed in each cohort. Operative times were comparable (P = .08). Postoperatively, complication rates were similar (P = .29), with no difference in ileus (P = 1.00). The length of stay (3.69 vs 3.49 days; P = .16), readmission (2.8% vs 3.7%; P = .66) and reoperation rates (2.2% vs 1.6%; P = .77) were comparable for alvimopan and controls, respectively. Total costs were similar ($14,932.47 alvimopan vs $14,846.56 controls; P = .90), but the additional costs in the alvimopan group could translate to savings of $27,577 in the cohort.

CONCLUSIONS

Alvimopan added no benefit in patient outcomes in laparoscopic colorectal surgery with an ERP. These results could drive a change in current practice. Controlled studies are warranted to define the cost and/or benefit in clinical practice.

Surgical advances in bladder cancer: at what cost?

Bladder cancer is the most expensive cancer to treat from diagnosis to death. Frequent disease recurrence, intense follow-up, and expensive, invasive techniques for diagnosis and treatment drive these costs for non-muscle invasive bladder cancer. Fluorescence cystoscopy increases the detection of superficial bladder cancer and reduces costs by improving the quality of resection and reducing recurrences. Radical cystectomy with intestinal diversion is the mainstay of treatment of invasive disease; however it is associated with substantial cost and morbidity. Increased efforts to improve the surgical management of bladder cancer while reducing the cost of treatment are increasingly necessary.

Postoperative ileus: mechanisms and future directions for research

Postoperative ileus (POI) is an abnormal pattern of gastrointestinal motility characterized by nausea, vomiting, abdominal distension and/or delayed passage of flatus or stool, which may occur following surgery. Postoperative ileus slows recovery, increases the risk of developing postoperative complications and confers a significant financial load on healthcare institutions. The aim of the present review is to provide a succinct overview of the clinical features and pathophysiological mechanisms of POI, with final comment on selected directions for future research.Terminology used when describing POI is inconsistent, with little differentiation made between the obligatory period of gut dysfunction seen after surgery ('normal POI') and the more clinically and pathologically significant entity of a 'prolonged POI'. Both normal and prolonged POI represent a fundamentally similar pathophysiological phenomenon. The aetiology of POI is postulated to be multifactorial, with principal mediators being inflammatory cell activation, autonomic dysfunction (both primarily and as part of the surgical stress response), agonism at gut opioid receptors, modulation of gastrointestinal hormone activity and electrolyte derangements. A final common pathway for these effectors is impaired contractility and motility and gut wall oedema. There are many potential directions for future research. In particular, there remains scope to accurately characterize the gastrointestinal dysfunction that underscores an ileus, development of an accurate risk stratification tool will facilitate early implementation of preventive measures and clinical appraisal of novel therapeutic strategies that target individual pathways in the pathogenesis of ileus warrant further investigation.

Alvimopan: A cost-effective tool to decrease cystectomy length of stay

INTRODUCTION

We sought to evaluate the cost effectiveness of perioperative use of alvimopan in cystectomy and urinary diversion. A recent randomized controlled trial demonstrated the efficacy of alvimopan in reducing postoperative ileus and length of stay in cystectomy; however, a major limitation was the exclusion of epidural analgesia.

MATERIALS AND METHODS

Eighty-six cystectomy and urinary diversion procedures performed by seven surgeons were analyzed between January 2008 and April 2012. The first 50 patients did not receive alvimopan perioperatively, while the subsequent 36 received a single dose of 12 mg preoperatively and then 12 mg every 12 hours for 15 doses or until discharge.

RESULTS

The groups were equal with respect to age, gender, indication, surgeon, and type of diversion. Patients who received alvimopan experienced a shorter length of stay (LOS) versus those in who did not receive alvimopan (10.5 vs. 8.6 days, p = 0.005, 95% CI 0.6-3.3). Readmission for ileus was low in both alvimopan and control groups (0% and 4.4%, respectively). Costs were significantly lower in the alvimopan group than the control groups (2012 USD 32,443 vs. 40,604 p <0.001). This difference stood up to multivariate analysis with a $7,062 difference in hospital stay.

CONCLUSIONS

Use of alvimopan in the routine perioperative care of our cystectomy and urinary diversion patients has decreased LOS by 1.9 days. Additionally, institution of routine perioperative alvimopan has reduced costs by $7,062 per admission (20% reduction). This demonstrates a real world application of alvimopan at a moderate volume center.

Facilitating return of bowel function after colorectal surgery: alvimopan and gum chewing

Postoperative ileus is common after colorectal surgery, and has a huge impact on hospital LOS. With the impeding cost crisis in the United States, safely reducing length of stay is essential. Chewing gum and pharmacological treatment with alvimopan are safe, simple tools to reduce postoperative ileus and its associated costs. Future research will determine if integrating these tools with laparoscopic procedures and enhanced recovery pathways is a best practice in colorectal surgery.

Anesthetic Routines: The Anesthesiologist's Role in GI Recovery and Postoperative Ileus

All patients undergoing bowel resection experience postoperative ileus, a transient cessation of bowel motility that prevents effective transit of intestinal contents or tolerance of oral intake, to varying degrees. An anesthesiologist plays a critical role, not only in the initiation of surgical anesthesia, but also with the selection and transition to effective postoperative analgesia regimens. Attempts to reduce the duration of postoperative ileus have prompted the study of various preoperative, perioperative, and postoperative regimens to facilitate gastrointestinal recovery. These include modifiable variables such as epidural anesthesia and analgesia, opioid-sparing anesthesia and analgesia, fluid restriction, colloid versus crystalloid combinations, prokinetic drugs, and use of the new peripherally acting mu-opioid receptor (PAM-OR) antagonists. Review and appropriate adaptation of these multiple modifiable interventions by anesthesiologists and their surgical colleagues will facilitate implementation of a best-practice management routine for bowel resection procedures that will benefit the patient and the healthcare system.

[Methylnaltrexone. A new approach for therapy of opioid-induced obstipation]

Chronic pain patients using opioids frequently suffer from constipation which compromises well-being. Such an opioid-induced gastro-intestinal complication can occur regularly in patients in palliative care as well as in analgesic sedated intensive care patients or during prolonged perioperative pain therapy. Discomfort and distress in the affected patients can be so severely pronounced that they would rather suffer from the pain than from the side effect of constipation. Conventional therapy can be insufficient in providing satisfactory relief of constipation, mostly because this opioid-induced bowel hypomotility can be laxative-resistant. Moreover, constipation does not decrease during the course of therapy as do other side effects. It is well known that opioid-induced constipation is mediated via activation of micro-opioid receptors in the gastrointestinal tract. Selective peripheral micro-receptor antagonists (such as methylnaltrexone, Relistor) can effectively treat opioid-induced constipation. An interference with central analgesia does not occur as the molecules cannot pass the blood-brain barrier due to their charged states. A reduction of opioid therapy or the development of withdrawal symptoms can be avoided. Studies have shown that methylnaltrexone is not only safe and efficient for chronically constipated palliative care patients but offers promising therapeutic options for further patient collectives.

Recent advances in the use of opioids for cancer pain

Opioids are the mainstay of treatment for moderate to severe cancer pain. In recent years there have been many advances in the use of opioids for cancer pain. Availability and consumption of opioids have increased and opioids other than morphine (including methadone, fentanyl, oxycodone) have become more widely used. Inter-individual variation in response to opioids has been identified as a significant challenge in the management of cancer pain. Many studies have been published demonstrating the benefits of opioid switching as a clinical maneuver to improve tolerability. Constipation has been recognized as a significant burden in cancer patients on opioids. Peripherally restricted opioid antagonists have been developed for the prevention and management of opioid induced constipation. The phenomenon of breakthrough pain has been characterized and novel modes of opioid administration (transmucosal, intranasal, sublingual) have been explored to facilitate improved management of breakthrough cancer pain. Advances have also been made in the realm of molecular biology. Pharmacogenetic studies have explored associations between clinical response to opioids and genetic variation at a DNA level. To date these studies have been small but future research may facilitate prospective prediction of response to individual drugs.

Peripherally acting mu-opioid receptor antagonists and postoperative ileus: mechanisms of action and clinical applicability

Postoperative ileus (POI), a transient cessation of coordinated bowel function after surgery, is an important health care problem. The etiology of POI is multifactorial and related to both the surgical and anesthetic pathways chosen. Opioids used to manage surgical pain can exacerbate POI, delaying gastrointestinal (GI) recovery. Peripherally acting mu-opioid receptor (PAM-OR) antagonists are designed to mitigate the deleterious effects of opioids on GI motility. This new class is investigational for POI management with the goal of accelerating the recovery of upper and lower GI tract function after bowel resection. In this review, we summarize the mechanisms by which POI occurs and the role of opioids and opioid receptors in the enteric nervous system, discuss the mechanism of action of PAM-OR antagonists, and review clinical pharmacology and Phase II/III POI trial results of methylnaltrexone and alvimopan. Finally, the role of anesthesiologists in managing POI in the context of a multimodal approach is discussed.

Novel opioid antagonists for opioid-induced bowel dysfunction and postoperative ileus

Peripherally acting mu-opioid receptor antagonists methylnaltrexone and alvimopan are a new class of drugs designed to reverse opioid-induced side-effects on the gastrointestinal system without compromising pain relief. This article gives an overview of the pharmacology, the efficacy, and adverse effects of these drugs. Both compounds seem to be generally well tolerated and effective for the treatment of opioid-related bowel dysfunction and postoperative ileus. Methylnaltrexone recently received approval by the US Food and Drug Administration (FDA) and the European Medicines Agency for treatment of opioid-related bowel dysfunction in patients with advanced illness. Alvimopan was recently approved by the FDA for treatment of postoperative ileus, but the use of the drug is restricted to inpatients because it has been associated with an increased rate of myocardial infarction. Further research should assess the effectiveness and safety of these drugs in clinical practice.

Alvimopan

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Development of peripheral opioid antagonists' new insights into opioid effects

The recent approval by the US Food and Drug Administration of 2 medications--methylnaltrexone and alvimopan--introduces a new class of therapeutic entities to clinicians. These peripherally acting mu-opioid receptor antagonists selectively reverse opioid actions mediated by receptors outside the central nervous system, while preserving centrally mediated analgesia. Methylnaltrexone, administered subcutaneously, has been approved in the United States, Europe, and Canada. In the United States, it is indicated for the treatment of opioid-induced constipation in patients with advanced illness (eg, cancer, AIDS) who are receiving palliative care, when response to laxative therapy has not been sufficient. Alvimopan, an orally administered medication, has been approved in the United States to facilitate recovery of gastrointestinal function after bowel resection and primary anastomosis. Clinical and laboratory studies performed during the development of these drugs have indicated that peripheral receptors mediate other opioid effects, including decreased gastric emptying, nausea and vomiting, pruritus, and urinary retention. Laboratory investigations with these compounds suggest that opioids affect fundamental cellular processes through mechanisms that were previously unknown. These mechanisms include modifications of human immunodeficiency virus penetration, tumor angiogenesis, vascular permeability, and bacterial virulence.

Clinical trial: alvimopan for the management of post-operative ileus after abdominal surgery: results of an international randomized, double-blind, multicentre, placebo-controlled clinical study

BACKGROUND

Post-operative ileus (POI) affects most patients undergoing abdominal surgery.

AIM

To evaluate the effect of alvimopan, a peripherally acting mu-opioid receptor antagonist, on POI by negating the impact of opioids on gastrointestinal (GI) motility without affecting analgesia in patients outside North America.

METHODS

Adult subjects undergoing open abdominal surgery (n = 911) randomly received oral alvimopan 6 or 12 mg, or placebo, 2 h before, and twice daily following surgery. Opioids were administered as intravenous patient-controlled analgesia (PCA) or bolus injection. Time to recovery of GI function was assessed principally using composite endpoints in subjects undergoing bowel resection (n = 738).

RESULTS

A nonsignificant reduction in mean time to tolerate solid food and either first flatus or bowel movement (primary endpoint) was observed for both alvimopan 6 and 12 mg; 8.5 h (95% CI: 0.9, 16.0) and 4.8 h (95% CI: -3.2, 12.8), respectively. However, an exploratory post hoc analysis showed that alvimopan was more effective in the PCA (n = 317) group than in the non-PCA (n = 318) group. Alvimopan was well tolerated and did not reverse analgesia.

CONCLUSION

Although the significant clinical effect of alvimopan on reducing POI observed in previous trials was not reproduced, this trial suggests potential benefit in bowel resection patients who received PCA.

Opioid-induced constipation in intensive care patients: relief in sight?

Constipation is the most common gastrointestinal complication associated with opioid therapy in chronic pain patients, and also frequently occurs in sedated intensive care unit patients. Conventional therapy may not provide sufficient relief from constipation, which can be severe enough to limit opioid use or the dose. In a recent study on terminally ill patients suffering from laxative-resistant opioid-induced constipation, Thomas and colleagues demonstrated subcutaneous methylnaltrexone to rapidly induce defecation. This appealing result might also have favourable prospects for intensive care patients, as their outcome is often codetermined by recovery of bowel functioning.

Alvimopan and COX-2 inhibition reverse opioid and inflammatory components of postoperative ileus

Our objective was to investigate the therapeutic potential of peripheral opioid antagonism with alvimopan and anti-inflammatory cyclooxygenase 2 (COX-2) inhibition in an animal model of postoperative ileus with pain management. Intestinal manipulation was conducted in mice and rats with or without postoperative morphine injection. Rodents were orally fed non-digestible fluorescein (FITC)-labelled dextran and transit measured after a period of 90 min. The immunomodulatory effects of morphine and alvimopan were determined on nitric oxide released from the organ cultured muscularis externa. Surgical manipulation of the intestine resulted in a delay in gastrointestinal transit after 24 h that worsened with exogenous morphine. Alvimopan did not significantly alter transit of control or manipulated animals, but significantly antagonized the transit delaying effects of morphine. However, when the inflammatory component was robust enough to obscure a further opioid induced delay in gastrointestinal transit, alvimopan ceased to be effective in improving postoperative intestinal function. Cyclooxygenase 2 inhibition significantly diminished the inflammatory component of postoperative ileus. Surgical manipulation resulted in an increased release of nitric oxide from the inflamed isolated muscularis externa in 24-h organ culture which was not altered by morphine or alvimopan. Two distinct mechanisms exist which participate in postoperative bowel dysfunction: a local inflammatory response which is antagonized by COX-2 inhibition, and a morphine-induced alteration in neural function which can be blocked with alvimopan.

Opioid-induced bowel dysfunction

Opioid-induced bowel dysfunction is a distressing condition that may persist indefinitely in the clinical setting. As we understand more about normal gastrointestinal (GI) physiology, we are also beginning to understand more fully how opioids cause bowel dysfunction. Current therapeutic interventions for opioid-induced bowel dysfunction can be burdensome and sometimes lack efficacy. Systemic opioid antagonists administered orally can induce laxation, but can unpredictably induce systemic or local GI tract withdrawal symptoms. Two new investigational agents, alvimopan and methylnaltrexone, are peripherally acting opioid antagonists that do not cross the blood-brain barrier. Studies to date show promise that these agents may relieve opioid-induced bowel dysfunction in a well-tolerated manner without reversing central analgesia.

Emerging pharmacologic options for treating postoperative ileus

PURPOSE

Characteristics of the ideal drug therapy for postoperative ileus (POI); the pharmacology, efficacy, and safety of currently available nonselective opioid antagonists and the new peripherally selective opioid antagonists methylnaltrexone and alvimopan for the treatment of POI; and formulary considerations associated with the introduction of these new POI drug therapies are discussed.

SUMMARY

The ideal drug therapy for treating POI would selectively antagonize the inhibitory effects on the gastrointestinal (GI) tract of all of the potential factors implicated in the pathophysiology of POI (neurogenic, inflammatory, hormonal, and pharmacologic mediators). The most promising target to date is inhibition of the adverse GI effects of endogenous and exogenous opioids. Selective inhibition of the mu-opioid receptors in the GI tract, without reversing centrally mediated opioid-induced analgesia, may be beneficial in reducing POI. The nonselective opioid antagonists naloxone and nalmefene have not been studied for POI, and they cross the blood-brain barrier. Therefore, they are not appropriate for preventing or treating POI. The peripherally selective opioid antagonist methylnaltrexone shortens the duration of POI and the hospital length of stay (LOS). Alvimopan, a more extensively studied peripherally selective opioid antagonist, has been shown to reduce the duration of POI, frequency of postoperative nausea and vomiting, and hospital LOS. Both methylnaltrexone and alvimopan also appear effective for treating opioid-induced constipation. Preliminary results of a long-term study of alvimopan safety have revealed some potential concerns, and the significance of the adverse effects must be understood before the most appropriate role of alvimopan in patient care can be determined. Restricting the prescribing of new POI drug therapies to certain types of patients, surgeries, and prescribers; incorporating these therapies into preoperative and postoperative policies, procedures, and protocols; and the potential cost savings from reducing hospital LOS are among the considerations in adding these agents to health-system formularies.

CONCLUSION

Peripherally selective opioid receptor antagonists are promising new drug therapies that can reduce the clinical and economic burden of POI.

Treatment of opioid-induced gut dysfunction

Opioid analgesics are the mainstay in the treatment of moderate-to-severe pain, yet their use is frequently associated with adverse effects, the most common and debilitating being constipation. Opioid-induced motor stasis results from blockade of gastrointestinal peristalsis and fluid secretion, and reflects the action of the endogenous opioid system in the gut. Methylnaltrexone and alvimopan are new investigational drugs that selectively target peripheral mu-opioid receptors because they are poorly absorbed in the intestine and do not enter the brain. Clinical studies have proved the concept that these drugs prevent opioid-induced bowel dysfunction without interfering with analgesia. As reviewed in this article, opioid receptor antagonists with a peripherally restricted site of action also hold therapeutic promise in postoperative ileus and chronic constipation due to the fact that they have been found to stimulate intestinal transit.

Meta-analysis: Alvimopan vs. placebo in the treatment of post-operative ileus

BACKGROUND

Alvimopan is a selective, competitive mu-opioid receptor antagonist with limited oral bioavailability which may be used to reduce length of post-operative ileus.

AIM

The study compared alvimopan with placebo following bowel resection or total abdominal hysterectomy.

METHODS

A meta-analysis of randomized-controlled trials published between 2001 and 2006 of alvimopan vs. placebo was performed. The primary efficacy end-points were composite measures of passage of flatus, stool, and tolerance of solid food (GI-3) and passage of stool and tolerance of solid food (GI-2). The incidence of treatment emergent adverse events was assessed.

RESULTS

Five trials matched the selection criteria, reporting on 2195 patients. A total of 1521 (69.3%) had alvimopan and 674 (30.7%) placebo. GI-3 significantly improved (hazard ratio 1.30; 95% confidence intervals 1.16, 1.45, P < 0.001), as did GI-2 (hazard ratio 1.61; 95% confidence intervals 1.26, 2.05, P < 0.001) on alvimopan 12 mg. Time to discharge (hazard ratio 1.26; 95% confidence intervals 1.13, 1.40, P < 0.001), time to bowel motion (hazard ratio 1.74; 95% confidence intervals 1.29, 2.35, P < 0.001), and time to solid food (hazard ratio 1.14; 95% confidence intervals 1.01, 1.30, P < 0.04) also improved significantly. No difference was noted in the incidence of treatment emergent adverse events.

CONCLUSIONS

Alvimopan showed significant advantages over placebo in restoring gastro-intestinal function, and reduced time to discharge following major abdominal surgery, with acceptable side effects.

Use of novel prokinetic agents to facilitate return of gastrointestinal motility in adult critically ill patients

PURPOSE OF REVIEW

Intolerance of enteral feeding due to impaired gastrointestinal motility is common in critically ill patients. Strategies to prevent or treat gastrointestinal hypomotility include the use of prokinetic agents. Many currently employed prokinetic agents are associated with serious adverse drug reactions. The novel prokinetic agents - alvimopan, tegaserod, and dexloxiglumide - are reviewed.

RECENT FINDINGS

Alvimopan exerts mixed, but generally favorable, effects on restoration of gastrointestinal motility in patients with postoperative ileus. The observation of increased opioid requirements (without increased pain scores) and associated clinical ramifications requires further study. Tegaserod stimulates the peristaltic reflex and improves motility in multiple sites along the gastrointestinal tract. Its efficacy in improving gastrointestinal hypomotility in the critically ill population has not yet been determined. Furthermore, its use has been associated with the development of ischemic colitis and increased requirement for abdominal/pelvic surgery. Dexloxiglumide may be beneficial for improving gastric emptying in critically ill patients, especially those receiving lipid-enriched enteral feeds.

SUMMARY

Novel prokinetic agents show promise for management of gastrointestinal hypomotility in the critically ill population. However, further study is required before these agents can be recommended for use.

Current gut-directed therapies for irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that can present with a wide array of symptoms that make treatment difficult. Current therapies are directed at relieving symptoms of abdominal pain or discomfort, bloating, constipation, and diarrhea. Pharmacologic agents used to treat IBS-associated pain include myorelaxants, peppermint oil, and peripherally acting opiates. Dicyclomine and hyoscyamine, the two myorelaxants available in the United States, have not been proven effective in reducing abdominal pain in patients with IBS. The efficacy of peppermint oil is debated, but methodological problems with existing studies preclude definitive judgment. Loperamide is ineffective for relief of abdominal pain. For IBS patients with excessive abdominal bloating, a small number of studies suggest that bacterial eradication with gut-directed antibiotics and bacterial reconstitution with nonpathogenic probiotics may reduce flatulence. For constipation-predominant (C-IBS) symptoms, current treatment options include fiber supplementation, polyethylene glycol, and tegaserod. Soluble fibers (ispaghula, calcium polycarbophil, psyllium) are more effective than insoluble fibers (wheat bran, corn fiber) in alleviating global symptoms and relieving constipation, although fiber in general has marginal benefit in treatment of overall IBS symptoms. Polyethylene glycol increases bowel frequency in chronic constipation, but its overall efficacy against IBS is unclear. Tegaserod, a 5-HT(4) agonist, demonstrates superiority over placebo in improving bowel frequency and stool consistency and alleviating abdominal pain and bloating in women with C-IBS. Overall global symptoms are modestly improved with tegaserod when compared with placebo. Additional agents under investigation for C-IBS include the ClC(2) chloride channel opener lubiprostone, mu-opioid receptor antagonist alvimopan, and 5-HT(4) agonist renzapride. For diarrhea-predominant (D-IBS) symptoms, available therapies include loperamide, alosetron, and clonidine. Alosetron, a 5-HT(3) antagonist, is superior to placebo for reducing bowel frequency, improving stool consistency, and relieving abdominal pain in women with D-IBS. However, alosetron is available under a restricted license because of concerns for ischemic colitis and severe constipation necessitating colectomy. Clonidine may be helpful in alleviating global symptoms for D-IBS patients.

The selective mu opioid receptor antagonist, alvimopan, improves delayed GI transit of postoperative ileus in rats

Postoperative ileus (POI) is often exacerbated by opioid analgesic use during and following surgery, since mu opioid receptor activation results in a further delay of gastrointestinal (GI) transit. The effects of alvimopan, a novel, selective, and peripherally acting mu opioid receptor antagonist, and the reference compound methylnaltrexone, upon POI were investigated in rats. Under isoflurane anesthesia, POI was induced by laparotomy with intestinal manipulation. Immediately after the surgery, the rats received (51)Cr by gavage. Three hours after the surgery, the rats were sacrificed and GI transit was estimated using the geometric center (GC) of (51)Cr. Alvimopan (0.1-3 mg/kg) or methylnaltrexone (100 mg/kg) were administered by gavage either before or after the surgery, with or without morphine administration (1 mg/kg). GI transit was delayed by intestinal manipulation (GC = 2.92 +/- 0.17). Alvimopan (1 and 3 mg/kg) significantly reversed this delayed GI transit when administered 45 min prior to surgery. However, the effects of alvimopan were less pronounced when administered following surgery. Morphine administration further delayed GI transit induced by intestinal manipulation (GC = 1.97 +/- 0.11). Under these conditions, alvimopan (1 and 3 mg/kg) also significantly improved delayed GI transit when administered before surgery. Methylnaltrexone was inactive under all experimental conditions. These data suggest that mu opioid receptors play a role in the pathogenesis of POI, and that the clinical benefit reported to be afforded by alvimopan may be in part mediated via inhibition of an endogenous opioid release as well as blockade of the unwanted GI actions of analgesic agents.

Anesthesia and analgesia during and after surgery in neonates

BACKGROUND

Historically, the use of anesthetics and analgesics in neonates and infants has been based on extrapolations from studies performed in adults and older children. Over the past 20 years, there has been a growing body of research on the clinical pharmacology and clinical outcomes of these agents in neonates and infants.

OBJECTIVE

This article summarizes clinical pharmacology and clinical outcomes studies of opioids, opioid antagonists, sedative-hypnotics, nonsteroidal anti-inflammatory drugs and acetaminophen, and local anesthetics in neonates and infants to highlight gaps in the available knowledge, review some concerns about study design, and identify drugs that should receive high priority for future study.

METHODS

Relevant studies were identified through a search of MEDLINE and a review of textbooks, conference proceedings, and abstracts. The available literature was subjected to expert committee-based review.

CONCLUSIONS

There is a growing body of information on analgesic and anesthetic pharmacokinetics, pharmacodynamics, and clinical outcomes in neonates and infants, permitting safe and effective use in some clinical settings. Major gaps in knowledge persist, however. Future research may involve a combination of clinical trials and preclinical studies in suitable infant animal surrogate models.

Basic and clinical pharmacology of new motility promoting agents

Recent research has provided new information about drugs that could be used to treat functional motility disorders. Promotility drugs accelerate gastric emptying or colonic transit and these properties may contribute to their efficacy in treating symptoms associated with gastroparesis, functional dyspepsia or constipation. 5-Hydroxytryptamine4 receptors are targets for drugs (tegaserod, renzapride) that treat symptoms in constipated irritable bowel syndrome patients and in gastroparesis. Drugs acting at motilin (erythromycin) and cholecystokinin-1 (dexloxiglumide) receptors accelerate gastric emptying. Dexloxiglumide might be useful in the treatment of functional dyspepsia particularly that associated with lipid intake. Alvimopan is a mu-opioid receptor antagonist that does not cross the blood brain barrier. Alvimopan is effective in treating postsurgical ileus and perhaps opiate-induced bowel dysfunction. Successes and failures of recent efforts to develop promotility agents revealed opportunities and challenges for developing new promotility drugs. The pharmacological properties of partial agonists might be exploited to develop effective promotility drugs. However, opposing actions of promotility agents on motility (increased contraction vs decreased accommodation) limit the clinical efficacy of drugs with these opposing actions. Selection of appropriate patient populations for evaluation of new drugs is also critical.

Alvimopan for the Management of Postoperative Ileus

OBJECTIVE:

To review the pharmacology, pharmacokinetics, clinical efficacy, safety, dosage, and administration of alvimopan, a peripherally acting μ-opioid receptor antagonist, in the management of postoperative ileus (POI).

DATA SOURCES:

A literature search (1980–October 2004%) applying the terms alvimopan, ADL 8–2698, and LY246736 was conducted using MEDLINE. Information was also obtained from scientific congress abstracts and data on file with the manufacturer.

STUDY SELECTION AND DATA EXTRACTION:

Studies and abstracts investigating alvimopan and POI were considered for inclusion; however, they were restricted to English-language articles.

DATA SYNTHESIS:

Alvimopan is a novel, peripherally acting μ-opioid receptor antagonist that is currently under evaluation for the management of POI. POI presents significant clinical challenges that can delay patient recovery and contribute to increased morbidity and prolonged hospitalization after surgery. Clinical trials have demonstrated that alvimopan, at oral doses of 6 and 12 mg, can accelerate time to recovery of gastrointestinal (GI) function and time to hospital discharge following abdominal surgery. The incidence of adverse events with alvimopan therapy was shown to be similar to that of placebo.

CONCLUSIONS:

Alvimopan is well tolerated and effective at accelerating GI recovery and time to discharge in patients who have undergone bowel resection or hysterectomy when administered prior to surgery and twice daily thereafter until discharge or for up to 7 days. Alvimopan potentially offers significant benefits for patients with POI over currently available treatments.

Alvimopan: an oral, peripherally acting, mu-opioid receptor antagonist for the treatment of opioid-induced bowel dysfunction--a 21-day treatment-randomized clinical trial

Alvimopan has been shown to reverse the inhibitory effect of opioids on gastrointestinal transit without affecting analgesia. We evaluated oral alvimopan, 0.5 or 1 mg, versus placebo, once daily for 21 days, in 168 patients with opioid-induced bowel dysfunction (OBD) who were receiving chronic opioid therapy (minimum, 1 month) for nonmalignant pain (n = 148) or opioid dependence (n = 20). The primary outcome was the proportion of patients having at least one bowel movement (BM) within 8 hours of study drug on each day during the 21-day treatment period. Averaged over the 21-day treatment period, 54%, 43%, and 29% of patients had a BM within 8 hours after alvimopan 1 mg, 0.5 mg, or placebo, respectively (P < .001). Secondary outcomes of median times to first BM were 3, 7, and 21 hours after initial doses of 1 mg, 0.5 mg, and placebo, respectively (P < .001; 1 mg vs placebo). Weekly BMs and overall patient satisfaction were increased after the 1-mg dose (P < .001 at weeks 1 and 2 vs placebo, and P = .046, respectively). Treatment-emergent adverse events were primarily bowel-related, occurred during the first week of treatment, and were of mild to moderate severity. Alvimopan was generally well tolerated and did not antagonize opioid analgesia. Patients treated with chronic opioid therapy often experience opioid-induced bowel dysfunction as a result of undesirable effects on peripheral opioid receptors located in the gastrointestinal tract. Alvimopan, a novel peripheral opioid mu-receptor antagonist, has demonstrated significant efficacy for the management of opioid-induced bowel dysfunction without compromise of centrally mediated opioid-induced analgesia.

Phase III trial of alvimopan, a novel, peripherally acting, mu opioid antagonist, for postoperative ileus after major abdominal surgery

PURPOSE

Postoperative ileus presents significant clinical challenges that potentially prolong hospital stay, contribute to readmission, and increase morbidity. There is no approved treatment for postoperative ileus. Alvimopan is a novel, peripherally acting, mu opioid receptor antagonist currently in development for the management of postoperative ileus.

METHODS

Patients undergoing partial colectomy or simple or radical hysterectomy were randomized to receive alvimopan 6 mg (n = 152), alvimopan 12 mg (n = 146), or placebo (n = 153) orally 2 hours before surgery and twice daily thereafter until discharge or for up to seven days. The primary efficacy end point, time to return of gastrointestinal function, was a composite measure of passage of flatus or stool and tolerating solid food. Secondary end points included time to the hospital discharge order written. Adverse events were monitored throughout the study.

RESULTS

Mean time to gastrointestinal recovery was significantly reduced in patients treated with alvimopan 6 mg vs. placebo (hazard ratio = 1.45; P = 0.003), with a smaller reduction seen with alvimopan 12 mg (hazard ratio = 1.28; P = 0.059). Mean time to the hospital discharge order written was significantly accelerated in patients treated with alvimopan 6 mg (hazard ratio = 1.50; P < 0.001). The most common treatment-emergent adverse events across all treatment groups were nausea, vomiting, and hypotension; the incidence of nausea and vomiting was reduced by 53 percent in the alvimopan 12-mg group.

CONCLUSIONS

In patients undergoing major abdominal surgery, alvimopan accelerated gastrointestinal recovery and time to the hospital discharge order written compared with placebo and was well tolerated.

Alvimopan, a selective peripherally acting mu-opioid antagonist

Alvimopan is a novel, peripherally acting mu-opioid antagonist that is being developed for the management of acute postoperative ileus and for the reversal of the delayed gastrointestinal and colonic transit that result in symptoms such as constipation, nausea and motility disorders in patients treated with opiate analgesics. There is a clinical need for effective medications for the treatment of postoperative ileus and opiate-induced constipation and other motility disorders. This review addresses the basic and applied pharmacology and current evidence for the use of the medication, alvimopan, in clinical gastroenterology.

Peripheral opiate action on afferent fibres supplying the rat intestine

The aim of the present study was to examine the sensitivity of mesenteric afferents supplying the rat small intestine to mu-opioid receptor ligands. Mesenteric afferent discharge was recorded electrophysiologically in response to [D-ALA2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO; 100 mug kg(-1) i.v.), before and after treatment with the mu-receptor antagonist alvimopan (1 mg kg(-1) i.v.). DAMGO markedly stimulated whole nerve mesenteric afferent discharge (P < 0.05), an effect completely blocked by alvimopan. The response of mesenteric afferents to 2-methyl-5-hydroxytryptamine (30 microg kg(-1) i.v.), bradykinin (0.1-1 microg kg(-1) i.a.) and both low- and high-threshold distension (0-60 mmHg) was unaffected by alvimopan. In chronically vagotomized animals, the low-threshold response to distension was attenuated while the remaining high-threshold response was unaffected by alvimopan. In conclusion, mesenteric afferent fibres are markedly stimulated by mu-opioid receptor agonists, an effect blocked by alvimopan, which may contribute to the gastrointestinal reflex and behavioural responses to opiate treatment or abuse. However, alvimopan did not influence the normal sensitivity of intestinal afferents to chemical and mechanical stimuli that activate different subpopulations of vagal and spinal afferents. Thus, alvimopan may be useful for the treatment of gastrointestinal sequelae following opiate treatment for postoperative or chronic pain.

The opioid system in the gastrointestinal tract

Mu-, delta- and kappa-opioid receptors (ORs) mediate the effects of endogenous opioids and opiate drugs. Here we report (1) the distribution of muOR in the guinea-pig and human gastrointestinal tract in relation to endogenous ligands, to functionally distinct structures in the gut and to deltaOR and kappaOR; and (2) the ligand-induced muOR endocytosis in enteric neurones using in vitro and in vivo models. In the guinea pig, muOR immunoreactivity is confined mainly to the myenteric plexus. MuOR myenteric neurones are most numerous in the small intestine, followed by the stomach and the proximal colon. MuOR immunoreactive fibres are dense in the muscle layer and the deep muscular plexus, where they are in close association with interstitial cells of Cajal. This distribution closely matches the pattern of enkephalin. MuOR enteric neurones comprise functionally distinct populations of neurones of the ascending and descending pathways of the peristaltic reflex. In human gut, muOR immunoreactivity is localized to myenteric and submucosal neurones and to immune cells of the lamina propria. DeltaOR immunoreactivity is located in both plexuses where it is predominantly in varicose fibres in the plexuses, muscle and mucosa, whereas kappaOR immunoreactivity appears to be confined to the myenteric plexus and to bundles of fibres in the muscle. MuOR undergoes endocytosis in a concentration-dependent manner, in vitro and in vivo. Pronounced muOR endocytosis is observed in neurones from animals that underwent abdominal surgery that has been shown to induce delay in gastrointestinal transit. We can conclude that all three ORs are localized to the enteric nervous system with differences among species, and that muOR endocytosis can be utilized as a means to visualize enteric neurones activated by opioids and sites of opioid release.

Opioids and opioid receptors in the enteric nervous system: from a problem in opioid analgesia to a possible new prokinetic therapy in humans

The gut is a neurological organ, which implies that many neuroactive drugs such as opioid analgesics can seriously disturb gastrointestinal function, because many of the transmitters and transmitter receptors present in the brain are also found in the enteric nervous system. One of the most common manifestations of opioid-induced bowel dysfunction is constipation which results from blockade of peristalsis and intestinal fluid secretion. The discovery of opioid receptor antagonists with a peripherally restricted site of action, such as N-methylnaltrexone and alvimopan, makes it possible to normalize bowel function in opiate-treated patients without compromising central opioid analgesia. There is emerging evidence that opioid receptor antagonists may also have prokinetic actions, reversing pathological states of gastrointestinal hypomotility that are due to overactivity of the enteric opioid system.

Opioids and the gut: pharmacology and current clinical experience

This article reviews the pharmacology and physiology of opiate receptors and the current and potential uses of opioid agonists and antagonists in clinical gastroenterology. Mu-receptors are involved in motor and sensory functions, and their modulation is established for treatment of diarrhea. Mu-antagonists have potential to reverse endogenous (e.g., postoperative ileus) or iatrogenic dysmotility (e.g., opioid bowel dysfunction). Modulation of the function of kappa-receptors may be a novel approach to control visceral pain in functional gut disorders. Results of formal testing of novel opioid modulators are keenly awaited.

Abdominal surgery induces μ opioid receptor endocytosis in enteric neurons of the guinea-pig ileum

Immunohistochemistry and confocal microscopy were used to investigate mu opioid receptor (muOR) internalization in enteric neurons of the guinea-pig ileum following abdominal surgery. The following surgical procedures were performed under halothane or isofluorane anesthesia: a) midline abdominal skin incision, b) laparotomy or c) laparotomy with intestinal manipulation. Gastrointestinal transit was evaluated by using a non-absorbable marker and measuring fecal pellet output. In neurons from normal and control (anesthesia alone) animals, muOR was predominantly at the cell surface. muOR endocytosis following skin incision was not significantly different from controls (21.2+/-3.5% vs. 13.7+/-2.1%, mean+/-S.E.M.), whereas it was significantly increased by laparotomy (46.5+/-6.1%; P<0.01 vs. controls) or laparotomy plus intestinal manipulation (40.5+/-6.1%; P<0.01 vs. controls) 30 min following surgery compared with controls. muOR endocytosis remained elevated at 4 h (38.6+/-1.2%; P<0.01 vs. controls), whereas it was similar to controls at 6 and 12 h (17.5+/-5.8% and 11.2+/-3.0%). muOR endocytosis occurred in cholinergic and nitrergic neurons. Gastrointestinal transit was significantly delayed by laparotomy or laparotomy plus intestinal manipulation (12.8+/-1.2 and 13.8+/-0.6 h vs. 7.0+/-0.5 in controls; P<0.01), but was not significantly changed by skin incision (8.2+/-0.6 h). The findings of the present study support the concept that the noxious stimulation caused by abdominal surgery induces release of endogenous opioids thus resulting in muOR endocytosis in neurochemically distinct enteric neurons. muOR internalization can serve as indirect evidence of opioid release and as a means to visualize neuronal pathways activated by opioids.