Opioid-induced bowel dysfunction: pathophysiology and management

Naloxegol: a review of its use in patients with opioid-induced constipation

Oral naloxegol (Movantik™, Moventig(®)), a peripherally acting μ-opioid receptor antagonist, inhibits opioid binding in μ-opioid receptors in the gastrointestinal tract. This article reviews the pharmacological properties of naloxegol and its clinical efficacy and tolerability in patients with opioid-induced constipation. It demonstrated clinical efficacy and was well tolerated in placebo-controlled trials in patients with non-cancer pain and opioid-induced constipation, including those with an inadequate response to laxatives, and was well tolerated in a long-term safety study. As a PEGylated naloxone derivative, naloxegol is associated with significant improvements in spontaneous bowel movements, while maintaining levels of opioid-related analgesia (a result of its reduced ability to cross the blood-brain barrier). Naloxegol is a useful option in the treatment of opioid-induced constipation.

Efficacy and safety of naloxegol in patients with opioid-induced constipation and laxative-inadequate response

BACKGROUND

Treatment options for patients with opioid-induced constipation (OIC) and inadequate response to laxatives (LIR) are few.

OBJECTIVE

Assess the efficacy and safety of orally administered naloxegol in patients with prospectively confirmed OIC and LIR.

METHODS

We analyzed pooled data from two identical randomized, double-blind, placebo-controlled, Phase 3 trials of naloxegol in patients with non-cancer pain, OIC and LIR in which naloxegol (12.5 mg, n = 240; 25 mg, n = 241) or placebo (n = 239) were administered daily. We assessed the response rates, time to first post-dose laxation, spontaneous bowel movements (SBMs), OIC symptoms and patient-reported outcomes over 12 weeks.

RESULTS

OIC response rates for the naloxegol 25-mg (p < 0.001) and the 12.5-mg (p = 0.005) LIR dose groups were higher than placebo. Median times to first post-dose SBM were 7.6, 19.2 and 41.1 hours for the naloxegol 25 mg, naloxegol 12.5 mg and placebo groups, respectively. Other SBM measures, daily symptoms of OIC, and both the Patient Assessment of Constipation - Symptoms and Patient Assessment of Constipation-Quality of Life scores improved from baseline with naloxegol treatment. Changes from baseline in opioid dose, pain scores and opioid withdrawal scores were similar among treatment groups.

CONCLUSIONS

Naloxegol was efficacious, generally safe and well tolerated in the patients with OIC and LIR, while preserving opioid analgesia. ClinicalTrials.gov identifiers: NCT01309841; NCT01323790.

Evolving paradigms in the treatment of opioid-induced bowel dysfunction

In recent years prescription of opioids has increased significantly. Although effective in pain management, bothersome gastrointestinal adverse effects are experienced by a substantial proportion of opioid-treated patients. This can lead to difficulties with therapy and subsequently inadequate pain relief. Collectively referred to as opioid-induced bowel dysfunction, these adverse effects are the result of binding of exogenous opioids to opioid receptors in the gastrointestinal tract. This leads to disturbance of three important gastrointestinal functions: motility, coordination of sphincter function and secretion. In the clinic this manifests in a wide range of symptoms such as reflux, bloating, abdominal cramping, hard, dry stools, and incomplete evacuation, although the most known adverse effect is opioid-induced constipation. Traditional treatment with laxatives is often insufficient, but in recent years a number of novel pharmacological approaches have been introduced. In this review the pathophysiology, symptomatology and prevalence of opioid-induced bowel dysfunction is presented along with the benefits and caveats of a suggested consensus definition for opioid-induced constipation. Finally, traditional treatment is appraised and compared with the latest pharmacological developments. In conclusion, opioid antagonists restricted to the periphery show promising results, but use of different definitions and outcome measures complicate comparison. However, an international working group has recently suggested a consensus definition for opioid-induced constipation and relevant outcome measures have also been proposed. If investigators within this field adapt the suggested consensus and include symptoms related to dysfunction of the upper gut, it will ease comparison and be a step forward in future research.

Prolonged-release oxycodone-naloxone for treatment of severe pain in patients with Parkinson's disease (PANDA): a double-blind, randomised, placebo-controlled trial

BACKGROUND

Pain is a common non-motor symptom of Parkinson's disease. We investigated the analgesic efficacy of prolonged-release oxycodone-naloxone (OXN PR) in patients with Parkinson's disease and chronic, severe pain.

METHODS

We did this phase 2 study in 47 secondary care centres in the Czech Republic, Germany, Hungary, Poland, Romania, Spain, and the UK. We enrolled patients with Hoehn and Yahr Stage II-IV Parkinson's disease, at least one type of severe pain, and an average 24-h pain score of at least 6 (assessed on an 11-point rating scale from 0=no pain to 10=pain as bad as you can imagine). Participants were randomly assigned (1:1) with a validated automated system (block size four) to either oral OXN PR or placebo for 16 weeks (starting dose oxycodone 5 mg, naloxone 2·5 mg, twice daily). Patients and investigators were masked to treatment assignment. The primary endpoint was average 24-h pain score at 16 weeks in the full analysis population. This study is registered with EudraCT (2011-002901-31) and ClinicalTrials.gov (NCT01439100).

FINDINGS

We enrolled 202 patients; 93 were assigned to OXN PR and 109 to placebo; the full analysis population consisted of 88 patients versus 106 patients. Least squares mean average 24-h pain score at 16 weeks in the full analysis population was 5·0 (95% CI 4·5 to 5·5) in the OXN PR group versus 5·6 (5·1 to 6·0) in the placebo group (difference -0·6, 95% CI -1·3 to 0·0; p=0·058). Similar proportions of patients in each group had adverse events (60/92 [65%] vs 76/109 [70%]), treatment-related adverse events (52/92 [57%] vs 62/109 [57%]), and serious adverse events (5/92 [5%] vs 7/109 [6%]). Treatment-related nausea was more common in the OXN PR group than in the placebo group (16/92 [17%] vs 10/109 [9%]), as was treatment-related constipation (16/92 [17%] vs 6/109 [6%]).

INTERPRETATION

The primary endpoint, based on the full analysis population at week 16, was not significant. Nonetheless, the results of this study highlight the potential efficacy of OXN PR for patients with Parkinson's disease-related pain and might warrant further research on OXN PR in this setting.

FUNDING

Mundipharma Research.

Safety, tolerability, pharmacokinetics, and pharmacodynamic effects of naloxegol at peripheral and central nervous system receptors in healthy male subjects: A single ascending-dose study

This randomized, double-blind, placebo-controlled, ascending-dose, crossover study evaluated single oral doses of naloxegol (NKTR-118; 8, 15, 30, 60, 125, 250, 500, and 1000 mg), a PEGylated derivative of naloxone, for safety and tolerability, antagonism of peripheral and central nervous system (CNS) effects of intravenous morphine, and pharmacokinetics. Healthy men were randomized 1:1 to naloxegol or naloxegol-matching placebo administered with morphine and lactulose in a 2-period crossover design. Periods were separated by a 5- to 7-day washout. Assessments included safety, tolerability, orocecal transit time (OCTT), pupillary miosis, and pharmacokinetics. The study was completed by 46 subjects. The most common adverse events were somnolence, dizziness, headache, and nausea. Greater reversal of morphine-induced delay in OCTT occurred with increasing naloxegol dose, demonstrating dose-ordered antagonism of morphine's peripheral gastrointestinal effects. Forty-four subjects showed no reversal of pupillary miosis; 2 showed potential partial reversal at 250 and 1000 mg, indicating negligible antagonism of morphine's CNS effects at doses ≤ 125 mg. Rapid absorption, linear pharmacokinetics up to 1000 mg, and low to moderate between-subject pharmacokinetic variability was observed. The pharmacokinetics of morphine or its glucuronide metabolites were unaltered by concurrent naloxegol administration. Naloxegol was generally safe and well tolerated at single doses up to 1000 mg.

The effects of morphine and methylnaltrexone on gastrointestinal pain in healthy male participants

BACKGROUND

Opioid antagonists are increasingly used to abolish the gastrointestinal side effects of opioids. However, they can potentially interfere with local analgesia exerted via opioid receptors in the gut. Thus, in the current study we aimed to explore the effect of rectal morphine before and after blocking opioid receptors outside the central nervous system with methylnaltrexone (MNTX).

METHODS

In this randomized, placebo controlled, cross-over study 15 healthy male participants received the following drugs at three separate sessions: (i) placebo, (ii) 30 mg morphine administered per rectum, or (iii) 12 mg MNTX given subcutaneously before 30 mg rectal morphine. At baseline and after drug administration peripheral and central effects of the drugs were assessed by experimental pain to the skin, muscle, rectum and pupillometry.

KEY RESULTS

Compared to placebo there was no local effect of morphine on mechanical rectal distension. In contrast, an increase in tolerated volume was seen following MNTX/morphine administration (p < 0.001), starting 7 min after dosing. Both morphine and MNTX/morphine had a central effect manifested as an increase in mechanical muscle pressure thresholds (both p < 0.001) and a decrease in pupil diameter (both p < 0.001). These effects occurred 30 min after dosing.

CONCLUSIONS & INFERENCES

No peripheral analgesic effect of morphine was found. Methodological shortcomings may have contributed to the lack of peripheral analgesia and thus, a peripheral morphine effect on rectal pain cannot be excluded. On the other hand, the combination of MNTX and morphine exerted a local effect on rectal distensions and seems to improve analgesia.

Treatment of failed back surgery syndrome in a forty-three-year-old man with high-dose oxycodone/naloxone

Introduction:

Failed back surgery syndrome (FBSS) is an increasing cause of chronic pain in most countries. This poses high costs to both patients and National Health Organizations.

Case Presentation:

In this report, multimodal pain management based on daily high-dose oxycodone/naloxone (OXN 180/90 mg) led to reduced patient's pain score and improved quality of life.

Conclusions:

Oxycodone/naloxone can be a good alternative for the management of FBSS when other interventional or pharmacologic strategies have failed. In this case report, higher doses than those recommended as a maximum daily ceiling (80/40 mg) were safely used in one selected patient with noncancer severe pain.

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

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

Divergent Effect of Dezocine, Morphine and Sufentanil on Intestinal Motor Function in Rats

BACKGROUND

Opioid induced bowel dysfunction is the most common side effect of preoperatively administrated morphine, fentanyl and its derivative. However, the influence of dezocine on intestinal mobility is rarely reported. This study was designed to investigate the effects of dezocine, morphine and sufentanil on both intestinal smooth muscle contraction and propulsion in rats.

METHODS

Contractile tension and frequency of isolated rat small intestine smooth muscle were measured using tension transducer after incubation with different concentrations of dezocine, morphine and sufentanil. The propulsive rate of methylene blue in rat intestinal tract was measured 30 minutes after intraperitoneal injection of morphine, sufentanil and dezocine. Percent of change in contractile tension and contraction frequency compared to baseline level were calculated to evaluate muscle contraction. Propulsive rate of methylene blue was calculated as the percentage of methylene blue moving distance in intestinal tract compared to the length of the small intestine.

RESULTS

Morphine and sufentanil significantly increased the contractile tension of isolated small intestine smooth muscle at high doses. The contraction frequency did not change significantly among the 3 tested doses. Increasing the dose of dezocine from 1.7 mg.L(-1) to 10.2 mg.L(-1) did not change either the contractile tension or the contraction frequency. The propulsive rate of methylene blue in intestinal tract was significantly decreased after the treatment with morphine, sufentanil and dezocine (45.6%, 43.7%, and 42.1% respectively) compared to control group(57.1%), while the difference among the 3 drug groups were not significant.

CONCLUSION

Morphine and sufentanil may dose dependently increase the contractile tension and contraction ability of isolated rat small intestine smooth muscle, while dezocine has no significant effect on intestine smooth muscle contraction. However, all these opioids might impair small intestinal propulsion.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Naloxegol , a new drug for the treatment of opioid-induced constipation

INTRODUCTION

With increasing chronic opioid use, opioid-induced constipation (OIC) is becoming a relevant clinical challenge. Presently, only few treatments have been demonstrated to be more effective than placebo in treating OIC but most of them have a restricted clinical application because of side effects. Naloxegol , an orally administered, peripherally acting, μ-opioid receptor antagonist (PAMORA), was developed for the treatment of OIC.

AREA COVERED

This review summarizes published information and presentations at meetings on the effects of naloxegol in OIC. Pharmacodynamic studies have demonstrated that naloxegol inhibits gastrointestinal opioid effects while preserving central analgesic actions. Phase II and Phase III studies in patients with non-cancer OIC have confirmed the efficacy of naloxegol to inhibit OIC, and the most consistent efficacy was seen with the 25 mg dose once daily. Adverse events were mainly gastrointestinal in origin and usually transient and mild. There were no signs of opioid withdrawal in the studies. Safety and tolerability were also shown in a long-term safety study. Regulatory authorities have recently approved the use of naloxegol in OIC.

EXPERT OPINION

Naloxegol is the first approved, orally available PAMORA. The drug has the potential to substantially improve management of OIC patients.

Long-term evaluation of combined prolonged-release oxycodone and naloxone in patients with moderate-to-severe chronic pain: pooled analysis of extension phases of two Phase III trials

BACKGROUND

While opioids provide effective analgesia, opioid-induced constipation (OIC) can severely impact quality of life and treatment compliance. This pooled analysis evaluated the maintenance of efficacy and safety during long-term treatment with combined oxycodone/naloxone prolonged-release tablets (OXN PR) in adults with moderate-to-severe chronic pain.

METHODS

Patients (N = 474) received open-label OXN PR during 52-week extension phases of two studies, having completed 12-week, double-blind, randomized treatment with oxycodone prolonged-release tablets (Oxy PR) or OXN PR. Analgesia and bowel function were assessed at each study visit using 'Average pain over last 24 h scale and Bowel Function Index (BFI), respectively. Treatment Satisfaction Questionnaire for Medication was assessed at study end only.

KEY RESULTS

Improvement in bowel function was particularly marked in patients who switched from Oxy PR in the double-blind phase to OXN PR during the extension phase, resulting in a clinically meaningful reduction (≥12 points) in BFI score: at the start of the extension phases, mean (SD) BFI score was 44.3 (28.13), and was 29.8 (26.36) for patients who had received OXN PR in the double-blind phase. One week later, BFI scores were similar for the two groups (26.5 [24.40] and 27.5 [25.60], respectively), as was observed throughout the following months. Fewer than 10% of patients received laxatives regularly. Mean 24-h pain scores were low and stable throughout the extension phases. No unexpected adverse events were observed.

CONCLUSIONS & INFERENCES

Pooled data demonstrate OXN PR is an effective long-term therapy for patients with chronic non-cancer pain, and can address symptoms of OIC. No new safety issues were observed which were attributable to the long-term administration of OXN PR.

Naloxegol for the treatment of opioid-induced constipation

With increasing chronic opioid use, opioid-induced constipation (OIC) is a rapidly increasing clinical challenge. Naloxegol, an orally administered, peripherally-acting, µ-opioid receptor antagonist, was developed for the treatment of OIC. This drug profile summarizes published information and presentations at meetings on the effects of naloxegol in OIC. In animal studies, naloxegol was able to inhibit gastrointestinal opioid effects while preserving central analgesic actions and human pharmacodynamic studies were in agreement with such mode of action. Phase II and Phase III studies in patients with non-cancer OIC confirmed the efficacy of naloxegol to inhibit OIC, and the most consistent efficacy was seen with the 25 mg dose once daily. There were no signs of opioid withdrawal in these studies. Side effects were mainly gastrointestinal in origin, and usually transient and mild. A long-term safety study showed no new adverse events. The US FDA and EMA are currently evaluating the use of naloxegol in OIC.

Fixed ratio (2:1) prolonged-release oxycodone/naloxone combination improves bowel function in patients with moderate-to-severe pain and opioid-induced constipation refractory to at least two classes of laxatives

OBJECTIVE

The effects of combined oxycodone/naloxone prolonged release tablets (OXN PR) were investigated in patients with moderate-to-severe chronic cancer-related or non-cancer pain. All patients had opioid-induced constipation (OIC) which persisted despite substantial laxative therapy.

RESEARCH DESIGN AND METHODS

This pooled analysis included 75 patients with OIC at study entry that was refractory to at least two laxatives with different modes of action. Patients completed randomized, double-blind treatment with OXN PR 20-120 mg/day for either 12 weeks (OXN 9001: non-cancer pain study) or 4 weeks (OXN 2001: cancer-related pain study). Analgesia and bowel function were assessed using the Brief Pain Inventory Short Form and Bowel Function Index (BFI), respectively. Use of laxative medication and safety were assessed throughout the studies.

CLINICAL TRIAL REGISTRATION

NCT00513656, EudraCT 2005-002398-57, EudraCT 2005-003510-15.

RESULTS

Statistically and clinically significant improvements in bowel function were observed following double-blind treatment with OXN PR. Mean (SD) reduction in BFI score was 21.2 (28.8) and comparable in patients with cancer-related (19.0 [28.9]) and non-cancer pain (23.3.[29.0]; P ≤ 0.0002). Furthermore, the proportion of patients with a BFI score within normal range (≤28.8) increased from 9.5% at screening to 43.1% at Day 15 of OXN PR. While all patients used ≥2 laxatives of different classes at screening, during study treatment 36% stopped using laxatives (P < 0.001). OXN PR provided effective analgesia, evidenced by stable pain scores during study treatment, and there were no unanticipated adverse events.

CONCLUSIONS

OXN PR significantly improved bowel function and reduced the use of laxatives in patients with OIC, previously unresponsive to at least two different classes of laxatives. OXN also provided effective analgesia for patients with moderate-to-severe cancer-related pain and non-cancer-related pain.

Clinical potential of naloxegol in the management of opioid-induced bowel dysfunction

Opioid-induced bowel dysfunction (OIBD) is a burdensome condition which limits the therapeutic benefit of analgesia. It affects the entire gastrointestinal tract, predominantly by activating opioid receptors in the enteric nervous system, resulting in a wide range of symptoms, such as reflux, bloating, abdominal cramping, hard, dry stools, and incomplete evacuation. The majority of studies evaluating OIBD focus on constipation experienced in approximately 60% of patients. Nevertheless, other presentations of OIBD seem to be equally frequent. Furthermore, laxative treatment is often insufficient, which in many patients results in decreased quality of life and discontinuation of opioid treatment. Novel mechanism-based pharmacological approaches targeting the gastrointestinal opioid receptors have been marketed recently and even more are in the pipeline. One strategy is prolonged release formulation of the opioid antagonist naloxone (which has limited systemic absorption) and oxycodone in a combined tablet. Another approach is peripherally acting, μ-opioid receptor antagonists (PAMORAs) that selectively target μ-opioid receptors in the gastrointestinal tract. However, in Europe the only PAMORA approved for OIBD is the subcutaneously administered methylnaltrexone. Alvimopan is an oral PAMORA, but only approved in the US for postoperative ileus in hospitalized patients. Finally, naloxegol is a novel, oral PAMORA expected to be approved soon. In this review, the prevalence and pathophysiology of OIBD is presented. As PAMORAs seem to be a promising approach, their potential effect is reviewed with special focus on naloxegol's pharmacological properties, data on safety, efficacy, and patient-focused perspectives. In conclusion, as naloxegol is administered orally once daily, has proven efficacious compared to placebo, has an acceptable safety profile, and can be used as add-on to existing pain treatment, it is a welcoming addition to the targeted treatment possibilities for OIBD.

Pharmacologic treatments for esophageal disorders

The following, from the 12th OESO World Conference: Cancers of the Esophagus, includes commentaries on the role for ketamine and other alternative treatments in esophageal disorders; the use of linaclotide in the treatment of esophageal pain; the alginate test as a diagnostic criterion in gastroesophageal reflux disease (GERD); the use of baclofen in treatment of GERD; the effects of opioids on the esophagus; the use of antagonists on the receptor level in GERD; the effect of local formulation of drugs on the esophageal mucosa; and the use of electroencephalographic fingerprints to predict the effect of pharmacological treatment.

Pre-operative opioid analgesia reduces clinical success of laparoscopic gastric electrical stimulation placement in patients with gastroparesis

INTRODUCTION

Gastroparesis is a common chronic and costly disorder for which medical therapy is often unsuccessful. Gastric electrical stimulation (GES) has been used to treat refractory cases, however, response is variable and difficult to predict. This study aims to assess whether pre-operative opioid analgesics (OA) use affects clinical success of GES.

METHODS

Records of 128 patients who underwent laparoscopic GES placement from March 2001 to September 2012 were analyzed retrospectively. Data collected included demographics, surgical outcomes, and clinical parameters. Pre- and post-operative opioid analgesic dosing (No = 0 morphine equivalents (ME)/day, Low = 0-40 ME/day, Mid = 41-80 ME/day, High >80 ME/day), as well as clinical symptom assessment was collected for up to 3 years post-operatively. Clinical success was defined as (1) OA reduction of >50 %, (2) maintenance of weight, or (3) symptom improvement. Descriptive statistics were computed for all factors. A p < 0.05 was considered statistically significant.

RESULTS

Fifty-three patients were on OA pre-operatively compared to 69 patients who were not. Patients not on OA pre-operatively were less likely than those on OA pre-op group to be on OA post-operatively (p = 0.005); however, there were no differences in weight or symptom improvement. Sub-group analysis of the 53 patients on OA demonstrated significant improvement in clinical symptoms in the low-morphine cohort compared to the mid-morphine cohort (p = 0.02), and OA dosing post-operatively in the low-morphine cohort diminished significantly compared to mid- and high-morphine cohort (p = 0.032). There was no significant difference in weight.

CONCLUSION

OA dosing pre-operatively significantly affects clinical success of GES placement. Criteria for offering GES implantation may need to take OA dosing into consideration.

Acetylcholine serves as a derepressor in Loperamide-induced Opioid-Induced Bowel Dysfunction (OIBD) in zebrafish

The mechanisms underlying gut development, especially peristalsis, are widely studied topics. However, the causes of gut peristalsis-related diseases, especially Opioid-Induced Bowel Dysfunction (OIBD) disorder, have not been well defined. Therefore, our study used zebrafish, a popular model for studying both gut development and peristalsis, and DCFH-DA, a dye that clearly labels the live fish gut lumen, to characterize the formation process of gut lumen as well as the gut movement style in vivo. By applying Loperamide Hydrochloride (LH), the μ-opioid receptor-specific agonist, we established an OIBD-like zebrafish model. Our study found that acetylcholine (ACh) was a key transmitter that derepressed the phenotype induced by LH. Overall, the study showed that the antagonistic role of ACh in the LH-mediated opioid pathway was evolutionarily conserved; moreover, the OIBD-like zebrafish model will be helpful in the future dissection of the molecular pathways involved in gut lumen development and pathology.

Clinical and economic evaluation of tapentadol extended release and oxycodone/naloxone extended release in comparison with controlled release oxycodone in musculoskeletal pain

OBJECTIVE

Chronic pain is a leading cause of disability and represents a relevant societal burden. Opioids are widely used for managing chronic non-cancer pain; however, the high incidence of side effects is often the main reason for discontinuation. Two formulations have recently been studied to improve the tolerability of opioids (tapentadol extended release [ER] and oxycodone/naloxone ER), but a direct comparison between these drugs is not available in the literature. The comparative cost effectiveness of these two drugs has not previously been assessed. The objective of this meta-analysis is a clinical and economic evaluation of tapentadol ER and oxycodone/naloxone ER for the treatment of musculoskeletal pain, by indirect comparison with controlled release (CR) oxycodone.

METHODS

A structured literature review was conducted to identify published data for the health-economic model. The authors performed a meta-analysis on three selected randomized controlled trials (RCTs) for each treatment (tapentadol ER and oxycodone/naloxone ER). As measure of treatment effect, risk ratio was calculated, compared to the control active treatment (CR oxycodone), for the following outcomes: discontinuation rate due to adverse events, due to gastrointestinal (GE) side effects and central nervous system (CNS) side effects. A Markov model was developed to compare the cost effectiveness of tapentadol ER and oxycodone/naloxone ER. Four health states were defined: (1) patients still on treatment; (2) occurrence of adverse events (gastroenterology, central nervous system); (3) treatment discontinuation as consequence of ineffectiveness of treatment; and (4) treatment discontinuation as consequence of adverse events.

RESULTS

Both drugs showed a significant clinical advantage over the active control, CR oxycodone; however, tapentadol ER resulted in a better risk ratio reduction for the primary outcome of discontinuation rate due to adverse events and for the secondary outcome nausea and vomiting. The two drugs gave equivalent results in the capacity of reduction of constipation risk. In the economic evaluation both interventions were cost effective compared with CR oxycodone. However, tapentadol ER showed the most favorable results as in 65% of cases it was less costly and produced a considerable quality adjusted life years (QALY) gain. The higher impact of tapentadol ER on the cost effectiveness results was probably due to the price and the lower incidence of adverse events and related discontinuation rate, resulting in a further economic advantage.

CONCLUSION

Both tapentadol ER and oxycodone/naloxone ER are cost effective interventions compared with CR oxycodone; however, tapentadol ER was shown to provide better clinical outcomes at lower costs.

Strategies for preventing side effects of systemic opioid in postoperative pediatric patients

BACKGROUND AND OBJECTIVES

Opioid is the gold standard for treating moderate-to-severe pain in pediatric patients. However, its undesirable side effects lead to unsatisfied postoperative pain management outcome (Pediatr Anesth, 17, 2007, 756). The most commonly reported opioid-related side effects are vomiting (40%), pruritus (20-60%) (Anesthesiology, 77, 1992, 162; Drugs, 67, 2007, 2323), and constipation (15-90%) (Int J Clin Pract, 61, 2007, 1181). The potential life-threatening adverse event, respiratory depression, is less common (0.0013%) (Pediatr Anesth, 20, 2010, 119). The aim of this review was to evaluate prevention strategies that have been shown to decrease opioid side effects in pediatric patients during the postoperative period.

METHODS

Literature searches were conducted from 1984 to February 2013. Meta-analysis, systematic review, and randomized, placebo-controlled studies were obtained from PubMed and the Cochrane Library. The medical subject heading (MeSH) terms were opioid analgesics, adverse effects, pediatrics, children, side effects, and postoperative pain.

RESULTS AND CONCLUSION

Data from 62 studies were reviewed. The strategies that could effectively prevent and reduce opioid side effects in pediatric patients during the postoperative period included minimizing the amount of opioid consumption by a multimodal approach, opioid titration, using local anesthetic techniques and providing the specific prophylaxis for each side effect.

Treatment of opioid-induced constipation: focus on the peripheral μ-opioid receptor antagonist methylnaltrexone

Most prescribed opioids exert their analgesic effects via activation of central μ-opioid receptors. However, μ-opioid receptors are also located in the gastrointestinal (GI) tract, and activation of these receptors by opioids can lead to GI-related adverse effects, in particular opioid-induced constipation (OIC). OIC has been associated with increased use of healthcare resources, increased healthcare costs, and decreased quality of life for patients. Nonpharmacologic (e.g., increased fiber uptake) and pharmacologic agents (e.g., laxatives) may be considered for the treatment and prevention of OIC. However, many interventions, such as laxatives alone, are generally insufficient to reverse OIC because they do not target the underlying cause of OIC, opioid activation of μ-opioid receptors in the GI tract. Therefore, there has been keen interest in antagonism of the μ-opioid receptor in the periphery to inhibit the effects of opioids in the GI tract. In this review, currently available pharmacologic therapies for the treatment and prevention of OIC are summarized briefly, with a primary focus on the administration of the peripheral μ-opioid receptor antagonist methylnaltrexone bromide in patients with OIC and advanced illness who are receiving palliative care. Also, clinical trial data of methylnaltrexone treatment in patients with OIC and other pain conditions (i.e., chronic noncancer pain and pain after orthopedic surgery) are reviewed. Data support that methylnaltrexone is efficacious for the treatment of OIC and has a favorable tolerability profile.

Physiology, signaling, and pharmacology of opioid receptors and their ligands in the gastrointestinal tract: current concepts and future perspectives

Opioid receptors are widely distributed in the human body and are crucially involved in numerous physiological processes. These include pain signaling in the central and the peripheral nervous system, reproduction, growth, respiration, and immunological response. Opioid receptors additionally play a major role in the gastrointestinal (GI) tract in physiological and pathophysiological conditions. This review discusses the physiology and pharmacology of the opioid system in the GI tract. We additionally focus on GI disorders and malfunctions, where pathophysiology involves the endogenous opioid system, such as opioid-induced bowel dysfunction, opioid-induced constipation or abdominal pain. Based on recent reports in the field of pharmacology and medicinal chemistry, we will also discuss the opportunities of targeting the opioid system, suggesting future treatment options for functional disorders and inflammatory states of the GI tract.

The colon: from banal to brilliant

The colon serves as the habitat for trillions of microbes, which it must maintain, regulate, and sequester. This is managed by what is termed the mucosal barrier. The mucosal barrier separates the gut flora from the host tissues; regulates the absorption of water, electrolytes, minerals, and vitamins; and facilitates host-flora interactions. Colonic homeostasis depends on a complex interaction between the microflora and the mucosal epithelium, immune system, vasculature, stroma, and nervous system. Disruptions in the colonic microenvironment such as changes in microbial composition, epithelial cell function/proliferation/differentiation, mucus production/makeup, immune function, diet, motility, or blood flow may have substantial local and systemic consequences. Understanding the complex activities of the colon in health and disease is important in drug development, as xenobiotics can impact all segments of the colon. Direct and indirect effects of pharmaceuticals on intestinal function can produce adverse findings in laboratory animals and humans and can negatively impact drug development. This review will discuss normal colon homeostasis with examples, where applicable, of xenobiotics that disrupt normal function.

Pain and chronic pancreatitis: A complex interplay of multiple mechanisms

Despite multiple theories on the pathogenesis of pain in chronic pancreatitis, no uniform and consistently successful treatment strategy exists and abdominal pain still remains the dominating symptom for most patients and a major challenge for clinicians. Traditional theories focussed on a mechanical cause of pain related to anatomical changes and evidence of increased ductal and interstitial pressures. These observations form the basis for surgical and endoscopic drainage procedures, but the outcome is variable and often unsatisfactory. This underscores the fact that other factors must contribute to pathogenesis of pain, and has shifted the focus towards a more complex neurobiological understanding of pain generation. Amongst other explanations for pain, experimental and human studies have provided evidence that pain perception at the peripheral level and central pain processing of the nociceptive information is altered in patients with chronic pancreatitis, and resembles that seen in neuropathic and chronic pain disorders. However, pain due to e.g., complications to the disease and adverse effects to treatment must not be overlooked as an additional source of pain. This review outlines the current theories on pain generation in chronic pancreatitis which is crucial in order to understand the complexity and limitations of current therapeutic approaches. Furthermore, it may also serve as an inspiration for further research and development of methods that can evaluate the relative contribution and interplay of different pain mechanisms in the individual patients, before they are subjected to more or less empirical treatment.

Pharmacological challenges in chronic pancreatitis

Drug absorption in patients with chronic pancreatitis might be affected by the pathophysiology of the disease. The exocrine pancreatic insufficiency is associated with changes in gastrointestinal intraluminal pH, motility disorder, bacterial overgrowth and changed pancreatic gland secretion. Together these factors can result in malabsorption and may also affect the efficacy of pharmacological intervention. The lifestyle of chronic pancreatitis patients may also contribute to gastrointestinal changes. Many patients limit their food intake because of the pain caused by eating and in some cases food intake is more or less substituted with alcohol, tobacco and coffee. Alcohol and drug interaction are known to influence the pharmacokinetics by altering either drug absorption or by affecting liver metabolism. Since patients suffering from chronic pancreatitis experience severe pain, opioids are often prescribed as pain treatment. Opioids have intrinsic effects on gastrointestinal motility and hence can modify the absorption of other drugs taken at the same time. Furthermore, the increased fluid absorption caused by opioids will decrease water available for drug dissolution and may hereby affect absorption of the drug. As stated above many factors can influence drug absorption and metabolism in patients with chronic pancreatitis. The factors may not have clinical relevance, but may explain inter-individual variations in responses to a given drug, in patients with chronic pancreatitis.

Pharmacological pain management in chronic pancreatitis

Intense abdominal pain is a prominent feature of chronic pancreatitis and its treatment remains a major clinical challenge. Basic studies of pancreatic nerves and experimental human pain research have provided evidence that pain processing is abnormal in these patients and in many cases resembles that seen in neuropathic and chronic pain disorders. An important ultimate outcome of such aberrant pain processing is that once the disease has advanced and the pathophysiological processes are firmly established, the generation of pain can become self-perpetuating and independent of the initial peripheral nociceptive drive. Consequently, the management of pain by traditional methods based on nociceptive deafferentation (e.g., surgery and visceral nerve blockade) becomes difficult and often ineffective. This novel and improved understanding of pain aetiology requires a paradigm shift in pain management of chronic pancreatitis. Modern mechanism based pain treatments taking into account altered pain processing are likely to increasingly replace invasive therapies targeting the nociceptive source, which should be reserved for special and carefully selected cases. In this review, we offer an overview of the current available pharmacological options for pain management in chronic pancreatitis. In addition, future options for pain management are discussed with special emphasis on personalized pain medicine and multidisciplinarity.

Medical influences, surgical outcomes: Role of common medications on the risk of perforation from untreated diverticular disease

Numerous drugs, largely used in the wards or at home, have a significant influence on patients with untreated diverticular disease. The consequences can be disastrous, may require an emergency operation, postoperative intensive care, and overall influence the patient’s length of stay and the final outcomes. Bearing these considerations in mind the routine or chronic administration of pain-killers, steroids and non-steroidal anti-inflammatory should be balanced in patients with known diverticular disease as it normally happens with other conditions potentially affected by these drugs (i.e., peptic ulcer disease or chronic obstructive pulmonary disease). This is even more important in the old and frail patient where an eventual surgical treatment may not always be possible.

Nutritional management of acute pancreatitis: the concept of 'gut rousing'

PURPOSE OF REVIEW

Enteral nutrition has emerged as one of the most effective treatments in the early management of patients with acute pancreatitis. The original rationale for nutrition in acute pancreatitis, dating back to the mid-20th century, was to provide full nutritional requirements but avoid stimulating exocrine pancreatic secretion. The purpose of this article is to review the recent clinical studies of enteral nutrition in acute pancreatitis to revise the rationale and develop a contemporary conceptual framework for nutritional management of this disease.

RECENT FINDINGS

Several recent randomized controlled trials dispel the outdated concept of 'pancreatic rest', which equates with gut neglect, and offer 'gut rousing' as a preferred concept. The new concept postulates that gastrointestinal (dys)function has a discernible impact on the outcomes of patients with acute pancreatitis. Further, timely administration of appropriate intraluminal modalities prevents or mitigates the gastrointestinal dysfunction.

SUMMARY

Nutritional management in acute pancreatitis should aim primarily at maintaining the gastrointestinal function. Providing full nutritional requirements and avoiding pancreatic exocrine stimulation should be considered as secondary aims.

Comparison of effects of epidural bupivacaine and intravenous meperidine analgesia on patient recovery following elective abdominal aortic surgery

Background

The efficacy of epidural anesthesia and analgesia in management of perioperative stress has been established. Perioperative pain management strategies decrease surgical complications and aid recovery. In this study, we aimed to document and compare the efficacy of epidural bupivacaine and intravenous meperidine on recovery of patients with elective abdominal aortic surgery performed under general anesthesia.

Material/Methods

Patients undergoing elective abdominal aortic surgery between February 2009 and November 2011 were studied prospectively. Patients were randomized into epidural bupivacaine (n=40) and intravenous meperidine (n=40) groups regarding postoperative analgesia strategy. The preoperative demographic characteristics, perioperative outcomes, postoperative adverse effects of analgesia strategy, time to initiate oral intake, sedation scores, visual analogue scale results, and mobility scores were compared.

Results

The mean ages of the patients were 61.7±8.1 in the epidural group and 59.4±9.7 in the intravenous group (p>0.05). The preoperative demographic characteristics of the patients were comparable between the groups. There were no statistically significant differences between groups regarding anesthesia times, intubation times, intensive care unit stay, hospital length of stay, postoperative vomiting, and postoperative cardiac, renal, and cerebral complications. Postoperative nausea was more prevalent in the meperidine group (p<0.05). In the epidural group, time to begin oral intake was shorter, sedation scores and visual analogue scale results were lower, and mobility scores were higher (p<0.05 each).

Conclusions

Epidural analgesia allowed earlier recovery compared to intravenous analgesia in patients undergoing elective abdominal aortic surgery, but did not affect postoperative outcomes and complications.

The place of oxycodone/naloxone in chronic pain management

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

Ligand-induced μ opioid receptor internalization in enteric neurons following chronic treatment with the opiate fentanyl

Morphine differs from most opiates its poor ability to internalize μ opioid receptors (μORs). However, chronic treatment with morphine produces adaptational changes at the dynamin level, which enhance the efficiency of acute morphine stimulation to promote μOR internalization in enteric neurons. This study tested the effect of chronic treatment with fentanyl, a μOR-internalizing agonist, on ligand-induced endocytosis and the expression of the intracellular trafficking proteins, dynamin and β-arrestin, in enteric neurons using organotypic cultures of the guinea pig ileum. In enteric neurons from guinea pigs chronically treated with fentanyl, μOR immunoreactivity was predominantly at the cell surface after acute exposure to morphine with a low level of μOR translocation, slightly higher than in neurons from naïve animals. This internalization was not due to morphine's direct effect, because it was also observed in neurons exposed to medium alone. By contrast, D-Ala2-N-Me-Phe4-Gly-ol5-enkephalin (DAMGO), a potent μOR-internalizing agonist, induced pronounced and rapid μOR endocytosis in enteric neurons from animals chronically treated with fentanyl or from naïve animals. Chronic fentanyl treatment did not alter dynamin or β-arrestin expression. These findings indicate that prolonged activation of μORs with an internalizing agonist such as fentanyl does not enhance the ability of acute morphine to trigger μOR endocytosis or induce changes in intracellular trafficking proteins, as observed with prolonged activation of μORs with a poorly internalizing agonist such as morphine. Cellular adaptations induced by chronic opiate treatment might be ligand dependent and vary with the agonist efficiency to induce receptor internalization.

Oxycodone combined with opioid receptor antagonists: efficacy and safety

INTRODUCTION

A mu receptor antagonist combined with oxycodone (OXY) may improve pain control, reduce physical tolerance and withdrawal, minimizing opioid-related bowel dysfunction and act as an abuse deterrent.

AREAS COVERED

The authors cover the use of OXY plus ultra-low-dose naltrexone for analgesia and the use of sustained-release OXY plus sustained-release naloxone to reduce the opioid bowel syndrome. The authors briefly describe the use of sustained-release OXY and naltrexone pellets as a drug abuse deterrent formulation. Combinations of ultra-low-dose naltrexone plus OXY have been in separate trials involved in patients with chronic pain from osteoarthritis and idiopathic low back pain. High attrition and marginal differences between ultra-low-dose naltrexone plus OXY and OXY led to discontinuation of development. Prolonged-release (PR) naloxone combined with PR OXY demonstrates a consistent reduction in opioid-related bowel dysfunction in multiple randomized controlled trials. However, gastrointestinal side effects, including diarrhea, were increased in several trials with the combination compared with PR OXY alone. Analgesia appeared to be maintained although non-inferiority to PR OXY is not formally established. There were flaws to trial design and safety monitoring. Naltrexone has been combined with OXY in individual pellets encased in a capsule. This combination has been reported in a Phase II trial and is presently undergoing Phase III studies.

EXPERT OPINION

Due to the lack of efficacy the combination of altered low-dose naltrexone with oxycodone should cease in development. The combination of sustained release oxycodone plus naloxone reduces constipation with a consistent benefit. Safety has been suboptimally evaluated which is a concern. Although the drug is commercially available in several countries, ongoing safety monitoring particularly high doses would be important.