Opioid-induced bowel dysfunction: pathophysiology and management

Intestinal barrier damage caused by addictive substance use disorder

Addictive substance use disorder has a wide range of effects on the intestinal barrier, including damage to the biological, chemical, mechanical, and immune barriers. Damage to the intestinal barrier caused by addictive substance use disorder allows harmful substances and bacteria to cross the intestinal barrier into the circulatory system, leading to systemic inflammatory responses and immune imbalances. In addition, the interaction between the gut flora and the central nervous system is recognized as an important component of the gut-brain axis. Gut barrier damage leads to dysbiosis, which in turn affects brain function by activating immune cells and releasing inflammatory factors. This may lead to altered mood and cognitive function, increased addictive substance cravings, and dependence. Recent research has indicated that reshaping the gut-brain axis and adjusting the composition and abundance of gut microbiota holds promise in alleviating withdrawal symptoms with addictive substance dependence. This article reviews the effects of addictive substance use disorder on the intestinal barrier and explores the possibility of improving addictive substance dependence by treating gut barrier damage.

Peripheral inflammation enhances opioid-induced gastrointestinal motility inhibition via up-regulating spinal mu opioid receptor

Opioids are potent analgesics in clinical pain management but exert variable analgesia in different pain types. Opioid-induced constipation is a common side effect of opioid therapy, and whether opioids induce different gastrointestinal motility inhibitions in different pain types is unknown. In this study, we evaluated the antinociceptive effects and inhibition of upper gastrointestinal transit and colonic bead expulsion of morphine, DAMGO, and Deltorphin in mouse CFA chronic inflammatory pain, SNI chronic neuropathic pain, and carrageenan chronic inflammatory pain models. Furthermore, quantitative PCR and immunofluorescence were used to investigate the mechanisms underlying the altered inhibition. Results showed that intrathecal administration of morphine, DAMGO, and Deltorphin produced higher antinociceptive effects in the CFA and carrageenan groups than in the SNI group. Upper gastrointestinal transit inhibition was significantly enhanced in the carrageenan group by morphine and DAMGO; colonic bead expulsion inhibition was also enhanced in the CFA and carrageenan groups by morphine and DAMGO, but not in Deltorphin treatment. Additionally, mu (MOR) opioid receptor mRNA and MOR-expressing cell density in the lumbar spinal cord of CFA and carrageenan mice were increased, whereas delta opioid receptor expression remained unchanged in these groups. Finally, the pharmacological blockade of MOR completely prevented the enhanced upper gastrointestinal transit inhibition in the carrageenan group by morphine and DAMGO. Altogether, our results indicate that gastrointestinal motility inhibition induced by MOR agonists can be enhanced with upregulated spinal MOR expression in chronic inflammatory pain.

Bilateral Rectus Sheath Block with Continuous Bupivacaine Infusions After Elective Open Gastrectomy: A Randomized Controlled Trial

Background and Objectives: Multimodal analgesia has been shown to be effective in facilitating early postoperative gastrointestinal function and rehabilitation in patients undergoing open gastrectomy. We conducted a clinical trial to investigate the effectiveness of bilateral rectus sheath block (RSB) with continuous bupivacaine infusion in comparison with placebo following elective open gastrectomy. Materials and Methods: Patients indicated for elective open gastrectomy were screened, enrolled, and randomised between October 2021 and September 2023. The patients were randomised to either Group A (intervention-continuous bupivacaine) or Group B (control-NaCl saline). The primary outcome measures were the quantity of an opioid analgesic administered during the initial 72 h post-surgery and the level of postoperative pain as indicated by the visual analogue scale (VAS). Mann-Whitney U test was used for quantitative analysis while Pearson Chi-square was used for categorical variables. Results: A total of 60 patients completed the trial, with 30 patients in each of the two groups. Patients in Group A reported lower median VAS pain scores at all observed time points following surgery (p < 0.001). No patient in Group A required rescue opioid analgesia, although non-steroidal anti-inflammatory drugs were necessary during the initial 12 h postoperatively. Clinically, Group A patients had a significantly shorter time to first gas (p = 0.001), a shorter time to first bowel movement (p < 0.001), a shorter time to first out-of-bed activity (p < 0.001), and a shorter overall hospitalisation duration (p < 0.001) compared to Group B patients. Conclusions: Bilateral RSB with continuous bupivacaine infusion is effective in managing pain and can reduce the use of opioid analgesics in the postoperative period. Furthermore, it promotes early recovery, and a shorter hospital stay.

Opioid-induced Constipation: Old and New Concepts in Diagnosis and Treatment

Daily use of opioid analgesics has significantly increased in recent years due to an increasing prevalence of conditions associated with chronic pain. Opioid-induced constipation (OIC) is one of the most common, under-recognized, and under-treated side effects of opioid analgesics. OIC significantly reduces the quality of life by causing psychological distress, lowering work productivity, and increasing access to healthcare facilities. The economic and social burden of OIC led to the development of precise strategies for daily clinical practice. Key aspects are the prevention of constipation through adequate water intake and fiber support, avoidance of sedentariness, and early recognition and treatment of cofactors that could worsen constipation. Recommended first-line therapy includes osmotic (preferably polyethylene glycol) and stimulant laxatives. Peripherally acting μ-opioid receptor antagonists, such as methylnaltrexone, naloxegol, or naldemedine, should be used in patients that have not responded to the first-line treatments. The bowel functional index is the main tool for assessing the severity of OIC and for monitoring the response. The paper discusses the recent literature on the pathophysiology, clinical evaluation, and management of OIC and provides a pragmatic approach for its assessment and treatment.

A Systematic Review of Naldemedine and Naloxegol for the Treatment of Opioid-Induced Constipation in Cancer Patients

BACKGROUND

Opioid-induced constipation (OIC) is a pervasive and distressing side effect of chronic opioid therapy in patients with cancer pain, significantly impacting their quality of life. Peripherally acting μ-opioid receptor antagonists (PAMORAS) were developed for treatment-resistant OIC but most studies were conducted with non-cancer patients.

OBJECTIVE

to discuss two oral formulations of PAMORAs, naldemedine and naloxegol, and to review available evidence of the effectiveness of these drugs for OIC in cancer patients.

METHODS

a comprehensive search to identify primary literature for either naldemedine or naloxegol for OIC in cancer patients.

RESULTS

Only three prospective randomized, double-blind, placebo-controlled clinical trials for naldemedine enrolling cancer patients were identified; the results of a subgroup analysis of two of those studies and two non-interventional post marketing surveillance studies of these trials are also reported here. For naloxegol, only two randomized controlled trials were identified; both were unsuccessful in enrolling sufficient patients. An additional four prospective non-interventional observational studies with naloxegol were found that enrolled cancer patients. There were significantly higher rates of responders in the PAMORA groups than in the placebo groups. The most common side effect for both PAMORAs was diarrhea.

LIMITATIONS

All studies were industry-funded, and given that only three trials were randomized controlled studies, the overall quality of the studies was lacking.

CONCLUSION

Naldemedine or naloxegol appeared safe and useful in the treatment of OIC in cancer patients and may improve their quality of life. Larger-scale randomized placebo-controlled studies of PAMORAs in cancer patients would strengthen existing evidence.

Prescription opioids induced microbial dysbiosis worsens severity of chronic pancreatitis and drives pain hypersensitivity

Opioids, such as morphine and oxycodone, are widely used for pain management associated with chronic pancreatitis (CP); however, their impact on the progression and pain sensitivity of CP has never been evaluated. This report investigates the impact of opioid use on the severity of CP, pain sensitivity, and the gut microbiome. C57BL/6 mice were divided into control, CP, CP with morphine/oxycodone, and either morphine or oxycodone alone groups. CP was induced by administration of caerulein (50ug/kg/h, i.p. hourly x7, twice a week for 10 weeks). The mouse-to-pancreas weight ratio, histology, and Sirius red staining were performed to measure CP severity. Tail flick and paw pressure assays were used to measure thermal and mechanical pain. DNA was extracted from the fecal samples and subjected to whole-genome shotgun sequencing. Germ-free mice were used to validate the role of gut microbiome in sensitizing acute pancreatic inflammation. Opioid treatment exacerbates CP by increasing pancreatic necrosis, fibrosis, and immune-cell infiltration. Opioid-treated CP mice exhibited enhanced pain hypersensitivity and showed distinct clustering of the gut microbiome compared to untreated CP mice, with severely compromised gut barrier integrity. Fecal microbiota transplantation (FMT) from opioid-treated CP mice into germ-free mice resulted in pancreatic inflammation in response to a suboptimal caerulein dose. Together, these analyses revealed that opioids worsen the severity of CP and induce significant alterations in pain sensitivity and the gut microbiome in a caerulein CP mouse model. Microbial dysbiosis plays an important role in sensitizing the host to pancreatic inflammation.

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.

Kidney Donor Perspectives on Acute Postoperative Pain Management

This study employed a qualitative descriptive approach to examine living kidney donor's experience of postoperative pain. Thirteen living kidney donors aged 46.5 (±14.4) years participated in this study. Semi-structured interviews were conducted and transcribed. Transcripts were inductively coded and reviewed for trends, patterns, and insights into donor's experience of postoperative pain. Donors experienced postoperative pain from a variety of sources that hindered recovery and created anxiety and fear in some. Donors managed pain with opioid and non-opioid medications, social support, and ambulation. Donor's past experiences with and expectations about pain, relationships with intended recipients, social support, as well as motivations for and meaning of donation informed their experience of postoperative pain. Prompt pharmacologic intervention for pain, as well as further coaching and education about pain management should be emphasized for nurses caring for living kidney donors. Further study of how donor's motivation might mediate their pain experience is needed.

Naldemedine-induced opioid withdrawal with restlessness as the predominant symptom in a palliative care setting

OBJECTIVES

Opioid analgesics play a central role in cancer pain treatment; however, it has been reported that opioid-induced constipation (OIC) develops in 80% of patients using opioid analgesics and leads to a decrease in quality of life. Naldemedine improves constipation without affecting the analgesic action of opioid analgesics via peripheral μ-opioid receptors.

METHODS

We report a terminally ill cancer patient who was diagnosed with opioid withdrawal syndrome (OWS) based on symptoms centered around restlessness and sweating that developed 43 days after administration of naldemedine for OIC.

RESULTS

The patient was a 78-year-old woman who was diagnosed with stage IVB uterine sarcoma in October, 1 year prior to her visit to our clinic,  and underwent chemotherapy after surgery, but the disease became progressive. Thereafter, metastasis to the fourth thoracic vertebrae (Th4) was identified, and loxoprofen and acetaminophen were started for pain at the metastatic site. Oxycodone hydrochloride hydrate 10 mg/day was additionally administered on postoperative day 11, followed by naldemedine 0.2 mg/day for OIC. On the 43rd day after administration, the patient began to wander the hospital ward in a wheelchair and became noticeably restless. OWS due to naldemedine administration was suspected, and naldemedine was discontinued. The symptoms improved 7 days later, and no similar symptoms were observed thereafter.

SIGNIFICANCE OF RESULTS

Patients receiving palliative care often exhibit psychiatric symptoms such as anxiety and depression, but OWS due to naldemedine should also be considered as a potential cause.

Ultrasound-Guided Blocks for Spine Surgery: Part 1-Cervix

Postoperative pain is common following spine surgery, particularly complex procedures. The main anesthetic efforts are focused on applying multimodal analgesia beforehand, and regional anesthesia is a critical component of it. The purpose of this study is to examine the existing techniques for regional anesthesia in cervical spine surgery and to determine their effect and safety on pain reduction and postoperative patient's recovery. The electronic databases were searched for all literature pertaining to cervical nerve block procedures. The following peripheral, cervical nerve blocks were selected and described: paravertebral block, cervical plexus clock, paraspinal interfascial plane blocks such as multifidus cervicis, retrolaminar, inter-semispinal and interfacial, as well as erector spinae plane block and stellate ganglion block. Clinicians should choose more superficial techniques in the cervical region, as they have been shown to be comparably effective and less hazardous compared to paravertebral blocks.

Overlap and cumulative effects of pancreatic duct obstruction, abnormal pain processing and psychological distress on patient-reported outcomes in chronic pancreatitis

OBJECTIVE

Several factors have been suggested to mediate pain in patients with chronic pancreatitis. However, it is unknown whether these factors are overlapping and if they have cumulative effects on patient-reported outcomes (PROs).

DESIGN

We performed a multicentre cross-sectional study of 201 prospectively enrolled subjects with definitive chronic pancreatitis. All subjects underwent evaluation for pancreatic duct obstruction, abnormalities in pain processing using quantitative sensory testing, and screening for psychological distress (anxiety, depression and pain catastrophising) based on validated questionnaires. Abnormality was defined by normal reference values. PROs included pain symptom severity (Brief Pain Inventory short form) and quality of life (EORTC-QLQ-C30 questionnaire). Associations between pain-related factors and PROs were investigated by linear trend analyses, multiple regression models and mediation analyses.

RESULTS

Clinical evaluation suggestive of pancreatic duct obstruction was observed in 29%, abnormal pain processing in 23%, anxiety in 47%, depression in 39% and pain catastrophising in 28%; each of these factors was associated with severity of at least one PRO. Two or more factors were present in 51% of subjects. With an increasing number of factors, there was an increase in pain severity scores (p<0.001) and pain interference scores (p<0.001), and a reduction in quality of life (p<0.001). All factors had independent and direct effects on PROs, with the strongest effect size observed for psychological distress.

CONCLUSION

Pain-related factors in chronic pancreatitis are often present in an overlapping manner and have a cumulative detrimental effect on PROs. These findings support a multidisciplinary strategy for pain management.

TRIAL REGISTRATION NUMBER

The study was registered with ClinicalTrials.gov (NCT03434392).

Oxycodone-Naloxone Combination Hinders Opioid Consumption in Osteoarthritic Chronic Low Back Pain: A Retrospective Study with Two Years of Follow-Up

Chronic low back pain (CLBP) due to osteoarthritis represents a therapeutic challenge worldwide. Opioids are extensively used to treat such pain, but the development of tolerance, i.e., less susceptibility to the effects of the opioid, which can result in a need for higher doses to achieve the same analgesic effect, may limit their use. Animal models suggest that ultra-low doses of opioid antagonists combined with opioid agonists can decrease or block the development of opioid tolerance. In this retrospective study, we tested this hypothesis in humans. In 2019, 53 patients suffering from CLBP were treated with either Oxycodone and Naloxone Prolonged Release (27 patients, OXN patients) or Oxycodone Controlled Release (26 patients, OXY patients). The follow-up period lasted 2 years, during which 10 patients discontinued the treatment, 5 out of each group. The remaining 43 patients reached and maintained the targeted pain relief, but at 18 and 24 months, the OXY patients showed a significantly higher oxycodone consumption than OXN patients to reach the same level of pain relief. No cases of respiratory depression or opioid abuse were reported. There were no significant differences in the incidence of adverse effects between the two treatments, except for constipation, more common in OXY patients. From our results, we can affirm that a long-term opioid treatment with oxycodone-naloxone combination, when compared with oxycodone only, may significantly hinder the development of opioid tolerance. We were also able to confirm, in our cohort, the well known positive effect of naloxone in terms of opioid-induced bowel dysfunction incidence reduction.

Regional gastrointestinal transit times in patients with chronic pancreatitis

The mechanisms behind disrupted gastrointestinal (GI) motor function in patients with chronic pancreatitis (CP) have not been fully elucidated. We compared regional transit times in patients with CP to those in healthy controls, and investigated whether they were associated with diabetes mellitus, exocrine dysfunction, opioid treatment or quality of life. Twenty-eight patients with CP and 28 age- and gender-matched healthy controls were included. Regional GI transit times were determined using the 3D-Transit system, which consists of an ingestible electromagnetic capsule and a detector worn in an abdominal belt for 5 days. Exocrine function was assessed using the fecal elastase-1 test, and quality of life was assessed using the European Organization for Research and Treatment of Cancer questionnaire. Transit times were analyzed for associations with diabetes mellitus, exocrine pancreatic insufficiency (EPI), opioid treatment and quality of life. Compared with healthy controls, patients with CP had prolonged transit times in the small intestine (6.6 ± 1.8 vs 4.8 ± 2.2 hours, P = .006), colon (40 ± 23 vs 28 ± 26 hours, P = .02), and total GI tract (52 ± 26 vs 36 ± 26 hours, P = .02). There was no difference in gastric emptying time (4.8 ± 5.2 vs 3.1 ± 1.3 hours, P = .9). No associations between transit times and diabetes, EPI, or opioid consumption were found (all P > .05). Quality of life and associated functional and symptom subscales were not associated with transit times, except for diarrhea (P = .03). Patients with CP have prolonged small intestinal and colonic transit times. However, these alterations do not seem to be mediated by diabetes, EPI, or opioid consumption.

Opioid Use, Gut Dysbiosis, Inflammation, and the Nervous System

Opioid use disorder (OUD) is defined as the chronic use or misuse of prescribed or illicitly obtained opioids and is characterized by clinically significant impairment. The etiology of OUD is multifactorial as it is influenced by genetics, environmental factors, stress response and behavior. Given the profound role of the gut microbiome in health and disease states, in recent years there has been a growing interest to explore interactions between the gut microbiome and the central nervous system as a causal link and potential therapeutic source for OUD. This review describes the role of the gut microbiome and opioid-induced immunopathological disturbances at the gut epithelial surface, which collectively contribute to OUD and perpetuate the vicious cycle of addiction and relapse.

Pancreatic QST Differentiates Chronic Pancreatitis Patients into Distinct Pain Phenotypes Independent of Psychiatric Comorbidities

BACKGROUND & AIMS

Quantitative sensory testing (QST) has been previously used to study pain in chronic pancreatitis (CP) but included methods that are not suitable for clinical purposes. The aims of this study were to determine if pancreatic QST (P-QST) can differentiate patients into distinct pain phenotypes and to determine the association of these with their clinical pain and psychiatric comorbidities.

METHODS

A multicenter cross-sectional study was conducted where patients completed validated questionnaires assessing quality of life (QoL), depression and anxiety scores as well as clinical pain symptoms followed by P-QST which included a cold pressor test, repetitive pinprick stimuli and pressure stimulation of the upper abdominal (T10) and control dermatomes. P-QST categorized patients into pain phenotypes based on a previously established nomogram. QoL, clinical pain and psychiatric assessment scores were compared across these groups.

RESULTS

A total of 179 patients were enrolled with a mean age of 54.1±13.6 years among whom 59% were males and 42% had an alcoholic etiology. P-QST showed no hyperalgesia in 91 (51%), segmental hyperalgesia in 50 (28%) and widespread hyperalgesia in 38 (21%) patients. Patients with widespread hyperalgesia had significantly higher pain intensity scores (P = .03) and rates of constant pain (P = .002) as well as decreased QoL (P < .001) and physical functioning (P =.03) in comparison with the other two pain phenotypes. In contrast, psychiatric comorbidities were similar across all groups.

CONCLUSIONS

P-QST may serve as a novel unbiased pain assessment tool in CP as it categorizes patients into distinct pain phenotypes independent of their psychiatric comorbidities.

Effects of codeine on esophageal peristalsis in humans using high resolution manometry

BACKGROUND AND AIM

Opioid receptors agonists have been demonstrated to impair lower esophageal sphincter (LES) relaxation and induce spastic esophageal dysmotility, but little was known for their impact on distension-induced secondary peristalsis. The aim of the study was to investigate the hypothesis whether acute administration of codeine can influence physiological characteristics of primary and secondary peristalsis in healthy adults.

METHODS

Eighteen healthy volunteers (13 men, mean age 27.5 years, aged 20-43 years) underwent high resolution manometry (HRM) with a catheter containing an injection port in mid-esophagus. Secondary peristalsis was performed with 10 and 20 mL rapid air injections. Two different sessions including acute administration of codeine (60 mg) or the placebo were randomly performed.

RESULTS

Codeine significantly increased 4-s integrated relaxation pressure (IRP-4s) (P = 0.003) and shortened distal latency (DL) (P = 0.003) of primary peristalsis. The IRP-4s of secondary peristalsis was also significantly higher after codeine than the placebo during air injections with 10 mL (P = 0.048) and 20 mL (P = 0.047). Codeine significantly increased the frequency of secondary peristalsis during air injections with 10 mL than the placebo (P = 0.007), but not for air injection with 20 mL (P = 0.305).

CONCLUSIONS

In addition to impair LES relaxation and reduce distal latency of primary peristalsis, codeine impairs LES relaxation of secondary peristalsis and increases secondary peristaltic frequency. Our study supports the notion in human esophagus that the impact of opioids on peristaltic physiology appears to be present in both primary and secondary peristalsis.

Can Naloxegol Therapy Improve Quality of Life in Patients with Advanced Cancer?

This observational study aims to evaluate the efficacy of naloxegol therapy in resolving opioid-induced constipation (OIC) and in improving the quality of life in a home palliative care cancer setting. Advanced cancer patients with OIC (Rome IV criteria) not relieved by laxatives started a naloxegol therapy 25 mg/day for 4 weeks. Quality of life was evaluated by Patient Assessment of Constipation Quality-of-Life (PAC-QoL) at day 0 and day 28; background pain by Numerical Rating Scale, number of weekly spontaneous bowel movements and Bowel Function Index (BFI) were evaluated at day 0 and every week. Seventy-eight patients who completed the 4-week study improved all four PAC-QoL dimensions (physical and psychological discomfort, worries/concerns and satisfaction level). Weekly spontaneous bowel movements increased and BFI improved. Background pain reduced after seven days and remained lower during the following weeks. Seventy-two patients dropped out the study before day 28 with a reduced survival compared to patients completing the study. Even in these patients, an improvement of bowel function was observed after two weeks. Naloxegol was effective in improving the quality of life, resolving OIC and reducing overall pain in patients with advanced cancer.

Tapentadol results in less deterioration of gastrointestinal function and symptoms than standard opioid therapy in healthy male volunteers

BACKGROUND

Tapentadol is a combined opioid agonist and norepinephrine reuptake inhibitor with fewer gastrointestinal side effects at equianalgesic doses compared with classical strong opioids. Previous studies on tapentadol have included multi-morbid patients in whom confounders exclude detailed assessment of the mechanistic effects and strict comparison with other opioids or placebo. This study aimed at investigating the effects of tapentadol and oxycodone on gastrointestinal motility and gastrointestinal side effects.

METHODS

21 healthy males participated in a randomized, double-blind, placebo-controlled, crossover study. Tapentadol (50 mg twice daily), oxycodone (10 mg twice daily), or placebo tablets were administered for 14 days. Segmental gastrointestinal transit times and colonic motility parameters were measured with electromagnetic capsules. Gastrointestinal side effects were assessed using questionnaires.

KEY RESULTS

During dosing with tapentadol, gastrointestinal side effects and motility parameters were on placebo level. Compared with tapentadol, oxycodone increased whole gut transit time by 17.9 hours (p = .015) and rectosigmoid transit time by 6.5 hours (p = .005). Compared with tapentadol, oxycodone also reduced long, fast antegrade colonic movements (p = .001). In comparison with placebo, oxycodone prolonged whole gut transit time by 31.6 hours, (p < .001). Moreover, less long, fast antegrade colonic movements (p = .002) were observed during oxycodone. For oxycodone only, slow colonic movements were associated with gastrointestinal side effects.

CONCLUSIONS & INFERENCES

In this mechanistic study, tapentadol caused significantly less colonic dysmotility and gastrointestinal side effects as compared with oxycodone in equianalgesic doses.

Psychopharmacologic Therapies for Irritable Bowel Syndrome

Psychopharmacologic therapies are beneficial in reducing symptoms when treating irritable bowel syndrome (IBS) and other disorders of gut-brain interaction (DGBI). Noradrenaline, serotonin, and dopamine are neurotransmitters of key importance in psychopharmacology and pain-reduction mechanisms. The first-line (tricyclic antidepressants, serotonin noradrenaline reuptake inhibitors, selective serotonin reuptake inhibitors) and second-line (atypical antipsychotics, delta-ligand agents, low-dose naltrexone) neuromodulator treatment options are recommended when IBS-associated abdominal pain is of moderate or severe intensity and is persistent. To understand the implementation strategy, the multidimensional clinical profile as a template is used for presenting 3 case scenarios involving painful IBS and DGBI of varying complexity.

Experimental considerations for the assessment of in vivo and in vitro opioid pharmacology

Morphine and other mu-opioid receptor (MOR) agonists remain the mainstay treatment of acute and prolonged pain states worldwide. The major limiting factor for continued use of these current opioids is the high incidence of side effects that result in loss of life and loss of quality of life. The development of novel opioids bereft, or much less potent, at inducing these side effects remains an intensive area of research, with multiple pharmacological strategies being explored. However, as with many G protein-coupled receptors (GPCRs), translation of promising candidates from in vitro characterisation to successful clinical candidates still represents a major challenge and attrition point. This review summarises the preclinical animal models used to evaluate the key opioid-induced behaviours of antinociception, respiratory depression, constipation and opioid-induced hyperalgesia and tolerance. We highlight the influence of distinct variables in the experimental protocols, as well as the potential implications for differences in receptor reserve in each system. Finally, we discuss how methods to assess opioid action in vivo and in vitro relate to each other in the context of bridging the translational gap in opioid drug discovery.

Management of Opioid-Induced Constipation and Bowel Dysfunction: Expert Opinion of an Italian Multidisciplinary Panel

The prescribing and use of opioid analgesics is increasing in Italy owing to a profusion in the number and types of opioid analgesic products available, and the increasing prevalence of conditions associated with severe pain, the latter being related to population aging. Herein we provide the expert opinion of an Italian multidisciplinary panel on the management of opioid-induced constipation (OIC) and bowel dysfunction. OIC and opioid-induced bowel dysfunction are well-recognised unwanted effects of treatment with opioid analgesics that can profoundly affect quality of life. OIC can be due to additional factors such as reduced mobility, a low-fibre diet, comorbidities, and concomitant medications. Fixed-dose combinations of opioids with mu (μ) opioid receptor antagonists, such as oxycodone/naloxone, have become available, but have limited utility in clinical practice because the individual components cannot be independently titrated, creating a risk of breakthrough pain as the dose is increased. A comprehensive prevention and management strategy for OIC should include interventions that aim to improve fibre and fluid intake, increase mobility or exercise, and restore bowel function without compromising pain control. Recommended first-line pharmacological treatment of OIC is with an osmotic laxative (preferably polyethylene glycol [macrogol]), or a stimulant laxative such as an anthraquinone. A second laxative with a complementary mechanism of action should be added in the event of an inadequate response. Second-line treatment with a peripherally acting μ opioid receptor antagonist (PAMORA), such as methylnaltrexone, naloxegol or naldemedine, should be considered in patients with OIC that has not responded to combination laxative treatment. Prokinetics or intestinal secretagogues, such as lubiprostone, may be appropriate in the third-line setting, but their use in OIC is off-label in Italy, and should therefore be restricted to settings such as specialist centres and clinical trials.

The Ameliorative Effects of Isorhynchophylline on Morphine Dependence Are Mediated Through the Microbiota-Gut-Brain Axis

Morphine abuse is a global public health problem. Increasing evidence has shown that gut microbiota dysbiosis plays an important role in several central nervous system diseases. However, whether there is an association between gut microbiota and morphine dependence remains unclear. In this study, the effects of isorhynchophylline on morphine dependence were evaluated based on the microbiota-gut-brain axis (MGBA). The results showed that isorhynchophylline could reverse the changes in alpha and beta diversity, composition, and richness of the intestinal flora occurring in morphine-dependent zebrafish, as well as the morphine-induced changes in the expression of MGBA-related genes in BV2 cells and the brain and intestine of zebrafish. Based on the results, we then used antibiotics to evaluate whether disrupting the gut microbiota would affect morphine addiction in zebrafish. The results showed that the antibiotic-induced intestinal floral imbalance changed the behavior of morphine-dependent zebrafish, the characteristics of the zebrafish intestinal flora, and the expression of MGBA-related genes in the zebrafish brain and intestine. Importantly, we also show that, following antibiotic administration, the ameliorative effects of isorhynchophylline on morphine addiction were lost. Together, our results indicate that the gut microbiota interacts with the brain, and dysbiosis of the intestinal flora may affect the efficacy of isorhynchophylline in the body. Our findings provide a novel framework for understanding the mechanisms of morphine addiction through the MGBA and may provide new therapeutic strategies for the use of Chinese medicines in the prevention of drug addiction.

Association between preoperative administration of gabapentinoids and 30-day hospital readmission: A retrospective hospital registry study

STUDY OBJECTIVE

To evaluate the effectiveness of preoperative gabapentinoid administration.

DESIGN

Retrospective hospital registry study.

SETTING

Tertiary referral center (Boston, MA).

PATIENTS

111,008 adult non-emergency, non-cardiac surgical patients between 2014 and 2018.

INTERVENTIONS

Preoperative administration of gabapentinoids (gabapentin or pregabalin).

MEASUREMENTS

We tested the primary hypothesis that preoperative gabapentinoid use was associated with lower odds of hospital readmission within 30 days. Contingent on this hypothesis, we examined whether lower intraoperative opioid utilization mediated this effect. Secondary outcome was postoperative respiratory complications.

MAIN RESULTS

Gabapentinoid administration was associated with lower odds of readmission (adjusted odds ratio [OR_adj] 0.80 [95% CI, 0.75-0.85]; p < 0.001). This effect was in part mediated by lower intraoperative opioid utilization in patients receiving gabapentinoids (8.2% [2.4-11.5%]; p = 0.012). Readmissions for gastrointestinal disorders (OR_adj 0.74 [0.60-0.90]; p = 0.003), neuro-psychiatric complications (OR_adj 0.66 [0.49-0.87]; p = 0.004), non-surgical site infections (OR_adj 0.68 [0.52-0.88; p = 0.004) and trauma or poisoning (OR_adj 0.25 [0.16-0.41]; p < 0.001) occurred less frequently in patients receiving gabapentinoids. The risk of postoperative respiratory complications was lower in patients receiving gabapentinoids (OR_adj 0.77 [0.70-0.85]; p < 0.001). Lower doses of pregabalin (< 75 mg) and gabapentin (< 300 mg) compared to both, no and high-dose administration of gabapentinoids, were associated with a lower risk of postoperative respiratory complications (OR_adj 0.61 [0.50-0.75]; p < 0.001 and OR_adj 0.70 [0.53-0.92]; p = 0.012, respectively). These lower gabapentinoid doses prevented 30-day readmission (OR_adj 0.74 [0.65-0.85]; p < 0.001). The results were robust in several sensitivity analyses including surgical procedure defined subgroups and patients undergoing ambulatory surgery.

CONCLUSIONS

The preoperative use of pregabalin and gabapentin, up to doses of 75 and 300 mg respectively, mitigates the risks of hospital readmission and postoperative respiratory complications which can in part be explained by lower intraoperative opioid use. Further research is warranted to elucidate mechanisms of the preventive action.

Validity and Reliability of the Hindi Version of the Patient Assessment of Constipation Quality of Life Questionnaire in Cancer Patients on Opioids for Pain Management at Tertiary Care Center, India

Background:

Opioid-induced constipation (OIC) causes a significant worsening of quality of life (QOL). The patient assessment of constipation QOL questionnaire (PAC-QOL) is a validated scale in English language to assess the QOL in patients with chronic constipation and guide the management by measuring response to a targeted therapy.

Objective:

The objective of the study was to evaluate the validity and reliability of PAC-QOL questionnaire after translation in Hindi language for Indian cancer patients with OIC.

Materials and Methods:

This was a prospective observational cross-sectional study. Three hundred and thirteen adult cancer patients receiving opioid treatment for pain and experiencing self-reported symptoms of constipation were evaluated. The severity of constipation was assessed at baseline and at an interval of at least 2 weeks by the physician using constipation scoring system (CSS) and self-reported Hindi version of PAC-QOL questionnaire.

Results:

The data obtained from 313 patients were taken for analysis. The internal consistency of the tool was established with the favorable value of Cronbach's alfa coefficient (i.e., >0.70) obtained for all four subgroups and overall score. The intraclass correlation coefficient value of >0.70 also established good correlation between overall and subgroups scores of Hindi version of PAC-QOL, obtained at 1^st and 2^nd visit. It was observed from the result that a significant correlation existed between the overall and subgroups scores of Hindi version of PAC-QOL and CSS, thus establishing concurrent validity.

Conclusion:

It was concluded from the study results that Hindi version of PAC-QOL is both reliable and valid to assess the QOL in patients with OIC.

Codeine induces increased resistance at the esophagogastric junction but has no effect on motility and bolus flow in the pharynx and upper esophageal sphincter in healthy volunteers: A randomized, double-blind, placebo-controlled, cross-over trial

BACKGROUND

Chronic opioid use can induce esophageal dysfunction with symptoms resembling achalasia and a manometric pattern of esophagogastric junction-outflow obstruction (EGJ-OO). However, the effect of opioids in acute setting on pharyngeal function and esophageal body contractility has not been investigated.

METHODS

After positioning the high-resolution impedance manometry (HRiM) catheter, codeine (60 mg) or placebo (glucose syrup) was infused intragastrically. Forty-five minutes post-infusion, participants received liquid, semi-solid, and solid boluses to assess esophageal and pharyngeal function. HRiM analysis was performed adhering to the Chicago classification v3.0. (CC v3.0). Pressure flow analysis (PFA) for the esophageal body and the pharynx was performed using the SwallowGateway™ online platform.

KEY RESULTS

Nineteen healthy volunteers (HV) [5 male; age 38.3] were included. After codeine administration, higher integrated relaxation pressure 4 s values resulted in significantly reduced deglutitive EGJ relaxation and distal latency was significantly shorter. Distal contractility was similar in both conditions. Bolus flow resistance at the EGJ and distention pressures increased significantly after codeine infusion. Based on CC v3.0, acute infusion of codeine induced EGJ-OO in six HV (p = 0.0003 vs. placebo). Codeine administration induced no significant alterations in any of the pharyngeal PFA metrics.

CONCLUSIONS & INFERENCES

In HV, acute administration of codeine increased bolus resistance at the EGJ secondary to induced incomplete EGJ relaxation leading to major motility disorders in a subset of subjects including EGJ-OO. However, an acute single dose of codeine did not affect motility or bolus flow in pharynx and UES. ClinicalTrials.gov number, NCT03784105.

Creating a bowel management plan for pediatric orthopaedic spine surgery patients

PURPOSE

Opioid-induced constipation is a common problem in patients who have undergone surgery. No standard gastrointestinal protocol exists to manage perioperative care in pediatric orthopaedic spinal fusion patients despite data which support the need for a bowel regimen while a patient is taking narcotics. At our institution, this group of patients often present to the emergency department with constipation and other gastrointestinal complaints. We developed a quality improvement initiative to create a standardized bowel management plan for pediatric patients undergoing orthopaedic spine surgery to decrease constipation, thus improving care, and minimizing unplanned visits.

METHODS

We developed a bowel management plan in collaboration with the gastroenterology team, created an Epic Smart Phrase for discharge instructions to enhance compliance, and created and dispersed informational communication on changes to constipation management. We monitored compliance, emergency department visits, and re-admissions.

RESULTS

Compliance with the bowel management plan, including inpatient medication prescribing and discharge "at-home" education, has increased to a mean of 93%. Emergency Department (ED) visits or re-admissions for constipation were reduced from a baseline mean of 1 in every 11 cases, to 1 in every 184 cases. Our institution sustained more than 2 years without an ED visit or readmission related to constipation in this patient population after the bowel management plan was in place.

CONCLUSION

A bowel management plan can be used in the care of pediatric spinal fusion patients to increase patient safety, decrease healthcare burden, and improve care. This project not only increased awareness of post-surgical gastrointestinal symptoms and opioid side effects, but also decreased post-operative emergency department visits and re-admissions related to constipation.

LEVEL OF EVIDENCE

III, case control study.

Pain Management in Chronic Pancreatitis: Summary of Clinical Practice, Current Challenges and Potential Contribution of the M-ANNHEIM Classification

Abdominal pain, diarrhea with weight loss, and endocrine insufficiency represent the dominant symptoms of chronic pancreatitis (CP). High intensity of pain and constant pain have been shown to reduce quality of life in CP and may result in disability and increased health resource utilization. Various basic challenges and unanswered questions still exist regarding the treatment of pain in CP. Recently, limited evidence has been gained that early surgery for painful disease might be associated with better treatment results. Thus, timing of pancreatic surgery in painful disease represents a major issue that needs to be clarified in future studies. In this context, surveillance of patients is necessary in clinical practice. It appears that a generally accepted classification of the disease represents a major requirement for inter-institutional comparison of data with future progress in clinical research. Among recently proposed classification systems, the M-ANNHEIM classification system of CP with its recently presented M-ANNHEIM Surgery Score might be a useful tool to picture the course of the disease and to monitor treatment results. Future research is required to clarify the possible role of this system in the management of pain in CP. In the present article, we provide an overview of current status, challenges, and unanswered questions in the treatment of pain in CP, and we demonstrate the potential benefits of the M-ANNHEIM classification system in the management of painful CP.

Delphi consensus on strategies in the management of opioid-induced constipation in cancer patients

BACKGROUND

Opioid-induced constipation (OIC) is a frequent and bothersome adverse event related with opioid therapy in cancer patients. Despite the high prevalence, medical management of OIC is often uncertain. The current project aimed to investigate expert opinion on OIC management and provide practical recommendations to improve the clinical approach of OIC in cancer patient.

METHODS

A modified Delphi method was conducted involving 46 different physicians experts in OIC. Using a structured questionnaire of 67 items this project intended to seek consensus on aspects related to diagnosis, treatment, and quality of life of cancer patients suffering with OIC.

RESULTS

After two rounds, a consensus was reached in 91% of the items proposed, all in agreement. Agreement was obtained on OIC definition (95.7%). Objective and patient-reported outcomes included in that definition should be assessed routinely in clinical practice. Responsive to symptom changes and easy-to-use assessment tools were recommended (87.2%). Successful diagnosis of OIC requires increase clinicians awareness of OIC and proactivity to discuss symptoms with their patients (100%). Successful management of OIC requires individualization of the treatment (100%), regular revaluation once is established, and keeping it for the duration of opioid treatment (91.5%). Oral Peripherally Acting μ-Opioid Receptor Agonists (PAMORAs), were considered good alternatives for the treatment of OIC in cancer patients (97.9%). This drugs and laxatives can be co-prescribed if OIC coexist with functional constipation.

CONCLUSIONS

The panelists, based on their expert clinical practice, presented a set of recommendations for the management of OIC in cancer patients.

Current overview of opioids in progression of inflammatory bowel disease; pharmacological and clinical considerations

Inflammatory bowel diseases (IBD) belong to a subgroup of persistent, long-term, progressive, and relapsing inflammatory conditions. IBD may spontaneously develop in the colon, resulting in tumor lesions in inflamed regions of the intestine, such as invasive carcinoma. The benefit of opioids for IBD treatment is still questionable, thereby we investigated databases to provide an overview in this context. This review demonstrates the controversial role of opioids in IBD therapy, their physiological and pharmacological functions in attenuating the IBD symptoms, and in improving inflammatory, oxidative stress, and the quality of life factors in IBD subjects. Data were extracted from clinical, in vitro, and in vivo studies in English, between 1995 and 2019, from PubMed, Google Scholar, Scopus, and Cochrane library. Based on recent reports, there are promising opportunities to target the opioid system and control the IBD symptoms. This study suggests a novel approach for future treatment of functional and inflammatory disorders such as IBD.

Pharmacological Characterization of µ-Opioid Receptor Agonists with Biased G Protein or β-Arrestin Signaling, and Computational Study of Conformational Changes during Receptor Activation

In recent years, G protein vs. β-arrestin biased agonism at opioid receptors has been proposed as an opportunity to produce antinociception with reduced adverse effects. However, at present this approach is highly debated, a reason why more information about biased ligands is required. While the practical relevance of bias in the case of µ-opioid receptors (MOP) still needs to be validated, it remains important to understand the basis of this bias of MOP (and other GPCRs). Recently, we reported two cyclopeptides with high affinity for MOP, the G protein biased Dmt-c[d-Lys-Phe-pCF3-Phe-Asp]NH2 (F-81), and the β-arrestin 2 biased Dmt-c[d-Lys-Phe-Asp]NH2 (C-33), as determined by calcium mobilization assay and bioluminescence resonance energy transfer-based assay. The biased character of F-81 and C-33 has been further analyzed in the [35S]GTPγS binding assay in human MOP-expressing cells, and the PathHunter enzyme complementation assay, used to measure β-arrestin 2 recruitment. To investigate the structural features of peptide-MOP complexes, we performed conformational analysis by NMR spectroscopy, molecular docking, and molecular dynamics simulation. These studies predicted that the two ligands form alternative complexes with MOP, engaging specific ligand-receptor contacts. This would induce different displays of the cytosolic side of the seven-helices bundle, in particular by stabilizing different angulations of helix 6, that could favor intracellular coupling to either G protein or β-arrestin.

Pharmacokinetics and pharmacodynamics of meperidine after intramuscular and subcutaneous administration in horses

OBJECTIVE

To describe the pharmacokinetics and pharmacodynamics of meperidine after IM and subcutaneous administration in horses.

STUDY DESIGN

prospective, randomized, blinded, crossover trial.

ANIMALS

Six adult horses weighing 494 ± 33 kg.

METHODS

Treatments included meperidine 1 mg/kg IM with saline 6 mL subcutaneously, meperidine 1 mg/kg subcutaneously with saline 6 mL IM, and saline 6 mL subcutaneously and 6 mL IM, with a 7-day washout between treatments. Plasma meperidine concentrations and pharmacodynamic values (thermal and mechanical thresholds, physiological variables, fecal production) were collected at various time points for 24 hours. Accelerometry data were obtained for 8 hours to measure locomotor activity. Data were analyzed with a mixed effects model, and α was set at .05.

RESULTS

Meperidine terminal half-life (T_1/2 ), maximal plasma concentrations, and time to maximal concentration were 186 ± 59 and 164 ± 56 minutes, 265.7 ± 47.2 and 243.1 ± 80.1 ng/mL at 17 ± 6, and 24 ± 13 minutes for IM at subcutaneous administration, respectively. No effect of treatment or time was observed on thermal or mechanical thresholds, heart rate, respiratory rate, locomotor activity, frequency of defecations, or fecal weight (P > .2 for all).

CONCLUSION

Maximum meperidine concentrations were achieved quickly with a short T_1/2 in both treatment groups. Neither IM nor subcutaneous meperidine influenced thermal or mechanical threshold or physiological variables.

CLINICAL SIGNIFICANCE

The short half-life and lack of detectable antinociceptive effect do not support IM or subcutaneous administration meperidine at 1 mg/kg for analgesia in horses.

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

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

Design, Synthesis and Functional Analysis of Cyclic Opioid Peptides with Dmt-Tic Pharmacophore

The opioid receptors are members of the G-protein-coupled receptor (GPCR) family and are known to modulate a variety of biological functions, including pain perception. Despite considerable advances, the mechanisms by which opioid agonists and antagonists interact with their receptors and exert their effect are still not completely understood. In this report, six new hybrids of the Dmt-Tic pharmacophore and cyclic peptides, which were shown before to have a high affinity for the µ-opioid receptor (MOR) were synthesized and characterized pharmacologically in calcium mobilization functional assays. All obtained ligands turned out to be selective antagonists of the δ-opioid receptor (DOR) and did not activate or block the MOR. The three-dimensional structural determinants responsible for the DOR antagonist properties of these analogs were further investigated by docking studies. The results indicate that these compounds attach to the DOR in a slightly different orientation with respect to the Dmt-Tic pharmacophore than Dmt-TicΨ[CH₂-NH]Phe-Phe-NH₂ (DIPP-NH₂[Ψ]), a prototypical DOR antagonist peptide. Key pharmacophoric contacts between the DOR and the ligands were maintained through an analogous spatial arrangement of pharmacophores, which could provide an explanation for the predicted high-affinity binding and the experimentally observed functional properties of the novel synthetic ligands.

The search for opioid analgesics with limited tolerance liability

Reducing the well-known side effects of opioids prescribed to treat chronic pain remains unresolved, despite extensive research in this field. Among several options to tackle this problem the synthesis of multifunctional compounds containing hybridized structures gained a lot of interest. Recently, extensively investigated are combinations of opioid agonist and antagonist pharmacophores embodied in a single molecule. To this end, agonism at the μ opioid receptor (MOR) with simultaneous antagonism at the δ opioid receptor (DOR) emerged as a promising avenue to obtaining novel analogs devoid of serious adverse effects associated with morphine-based analgesics. In this review we covered up-to-date research on the synthesis of peptide-based ligands with MOR agonist/DOR antagonist profile.

A retrospective evaluation of the effect of perianesthetic hydromorphone administration on the incidence of postanesthetic signs of colic in horses

OBJECTIVE

To describe the incidence of postanesthetic signs of colic (PASC) in horses and determine if perianesthetic administration of hydromorphone was associated with an increased risk of PASC.

STUDY DESIGN

Retrospective, cohort study.

ANIMALS

A total of 409 horses.

METHODS

Anesthesia and clinical records of horses admitted for various procedures from July 2018 to September 2019 were reviewed. Signs of colic and interventions were recorded up to 48 hours after anesthesia. A binomial logistic regression model was used to evaluate the association between the type of surgery, administration of hydromorphone, the duration of anesthesia and the incidence of PASC.

RESULTS

Overall, 25 (6.1%) horses developed PASC within 48 hours of general anesthesia. Of 60 horses that underwent colic surgery, 16 (26.7%) developed PASC. Of 349 horses that underwent noncolic procedures, nine (2.6%) developed PASC. Thus, the incidence of PASC was higher in horses that underwent colic surgery than in horses that underwent noncolic procedures [odds ratio (OR) = 13.74 (5.73-32.95)]. No effect of hydromorphone on the incidence of PASC was identified [OR = 1.61 (0.71-3.62)]. Longer procedures (>2 hours) were identified as an independent risk factor for PASC [OR = 4.13 (1.52-11.22)].

CONCLUSIONS

No association between hydromorphone and an increase in the incidence of PASC was identified. Anesthesia for colic surgery and duration of anesthesia were associated with an increased risk of PASC.

CLINICAL RELEVANCE

Hydromorphone did not increase the incidence of PASC in this population.

Biased Agonism as an Emerging Strategy in the Search for Better Opioid Analgesics

Morphine and related drugs that act through activating opioid receptors are the most effective analgesics for the relief of severe pain. They have been used for decades, despite the range of unwanted side effects that they produce, as no alternative has been found so far. The major goal of opioid research is to understand the mechanism of action of opioid receptor agonists and to improve the therapeutic utility of opioid drugs. In the search for safer and more potent analgesics, analogs with mixed opioid receptor profile gained a lot of interest. However, recently the concept of biased agonism, that highlights the fact that some ligands are able to differentially activate receptor downstream pathways, became a new approach in the design of novel drug candidates for clinical application. In this review, we summarize current knowledge on the development of opioid ligands of peptide and nonpeptide structure, showing how much opioid pharmacology evolved in recent years.

Ambulatory assessment of colonic motility using the electromagnetic capsule tracking system: Effect of opioids

BACKGROUND

Opioid treatment often causes debilitating constipation. However, it is not well described how opioids affect colonic motility and whether opioid-induced constipation is due to either a decrease of powerful peristaltic contractions or "uncoordinated" peristalsis. The present study aims to investigate the effect of oxycodone on parameters of colonic motility and to determine whether motility is normalized by the opioid antagonist naloxegol.

METHODS

In two randomized, double-blind crossover trials, oxycodone or placebo was administered to 25 healthy males (Trial A), while another 24 healthy males were administered oxycodone with naloxegol or placebo (Trial B). Colonic motility was assessed by tracking the progression of an electromagnetic capsule throughout the large intestine. Segmental colonic transit times and capsule movements were calculated using displacement distance and velocity.

KEY RESULTS

In Trial A, colonic transit time increased during oxycodone treatment compared with placebo (39 vs 18 hours, P < .01). Displacement during long fast antegrade movements was shorter during oxycodone treatment than with placebo (10 vs 20 cm, P = .03). In Trial B, colonic transit time was faster during oxycodone + naloxegol than during oxycodone + placebo (40 vs 55 hours, P = .049), mainly caused by an increase of the percentwise fraction of distance covered by fast movements in the left colon (P = .001).

CONCLUSION & INFERENCES

Oxycodone treatment impaired colonic motility, manifested as increased transit time, specifically decreased long fast antegrade movements, and addition of naloxegol improved motility dynamics. In humans, the increased transit time during opioid treatment is caused by a decrease in long fast movements rather than uncoordinated peristalsis.

Gastrointestinal pain

Gastrointestinal (GI) pain - a form of visceral pain - is common in some disorders, such as irritable bowel syndrome, Crohn's disease and pancreatitis. However, identifying the cause of GI pain frequently represents a diagnostic challenge as the clinical presentation is often blurred by concomitant autonomic and somatic symptoms. In addition, GI pain can be nociceptive, neuropathic and associated with cancer, but in many cases multiple aetiologies coexist in an individual patient. Mechanisms of GI pain are complex and include both peripheral and central sensitization and the involvement of the autonomic nervous system, which has a role in generating the symptoms that frequently accompany pain. Treatment of GI pain depends on the precise type of pain and the primary disorder in the patient but can include, for example, pharmacological therapy, cognitive behavioural therapies, invasive surgical procedures, endoscopic procedures and lifestyle alterations. Owing to the major differences between organ involvement, disease mechanisms and individual factors, treatment always needs to be personalized and some data suggest that phenotyping and subsequent individual management of GI pain might be options in the future.

Codeine delays gastric emptying through inhibition of gastric motility as assessed with a novel diagnostic intragastric balloon catheter

BACKGROUND

The use of opioids as analgesic is on the rise, despite their inhibitory effect on gastric emptying. A novel feeding catheter with integrated intragastric balloon was developed to continuously assess gastric motility, enabling to investigate the effect of opioids on motility and emptying simultaneously. We aimed to discriminate normal and pharmacologically impaired gastric motility and its impact on gastric emptying in healthy adults.

METHODS

The VIPUN Gastric Monitoring System comprises a nasogastric balloon catheter and a monitoring unit. In a four-way randomized, single-blinded, cross-over study, subjects received either placebo or 58.8 mg codeine phosphate in combination with either an uninflated or an inflated (180 mL) balloon catheter. Motility-induced pressure changes were recorded for 6 hours. During the first 2 hours, nutrients were infused (225 kcal, 75 mL/h). Gastric emptying was assessed with a ¹³ C-octanoate breath test and expressed as gastric half-emptying time (GET½). An algorithm, designed to detect phasic contractility, converted pressure changes to a gastric balloon motility index (GBMI). Results are presented as mean(SD).

KEY RESULTS

Eighteen subjects completed the investigation (32(13) years, 22(2) kg/m² ). After codeine, GBMI was lower (0.31(0.16)) and GET½ was longer (233(57) minutes) compared with placebo (GBMI: 0.48(0.15), P < .01 and GET½: 172(12) minutes, P < .001). Within-subject ΔGET½ correlated significantly with ΔGBMI (r = -0.77 and P < .001).

CONCLUSIONS AND INFERENCES

The VIPUN Gastric Monitoring System allowed to assess gastric motility safely and continuously. The correlation between pharmacologically decreased gastric emptying and motility indicates a strong link between both. Gastric motility, measured with this innovative device, can be an indicator for gastrointestinal intolerance.

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

OPINION STATEMENT

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

Discovery of Axelopran (TD-1211): A Peripherally Restricted μ-Opioid Receptor Antagonist

The effects of opioids in the central nervous system (CNS) provide significant benefit in the treatment of pain but can also lead to physical dependence and addiction, which has contributed to a growing opioid epidemic in the United States. Gastrointestinal dysfunction is an additional serious consequence of opioid use, and this can be treated with a localized drug distribution of a non-CNS penetrant, peripherally restricted opioid receptor antagonist. Herein, we describe the application of Theravance's multivalent approach to drug discovery coupled with a physicochemical property design strategy by which the N-substituted-endo-3-(8-aza-bicyclo[3.2.1]oct-3-yl)-phenyl carboxamide series of μ-opioid receptor antagonists was optimized to afford the orally absorbed, non-CNS penetrant, Phase 3 ready clinical compound axelopran (TD-1211) 19i as a potential treatment for opioid-induced constipation.

Pharmacokinetics and pharmacodynamics of hydromorphone after intravenous and intramuscular administration in horses

OBJECTIVE

To compare the pharmacokinetics and pharmacodynamics of hydromorphone in horses after intravenous (IV) and intramuscular (IM) administration.

STUDY DESIGN

Randomized, masked, crossover design.

ANIMALS

A total of six adult horses weighing [mean ± standard deviation (SD))] 447 ± 61 kg.

METHODS

Horses were administered three treatments with a 7 day washout. Treatments were hydromorphone 0.04 mg kg^⁻1 IV with saline administered IM (H-IV), hydromorphone 0.04 mg kg^⁻1 IM with saline IV (H-IM), or saline IV and IM (P). Blood was collected for hydromorphone plasma concentration at multiple time points for 24 hours after treatments. Pharmacodynamic data were collected for 24 hours after treatments. Variables included thermal nociceptive threshold, heart rate (HR), respiratory frequency (f_R), rectal temperature, and fecal weight. Data were analyzed using mixed-effects linear models. A p value of less than 0.05 was considered statistically significant.

RESULTS

The mean ± SD hydromorphone terminal half-life (t_1/2), clearance and volume of distribution of H-IV were 19 ± 8 minutes, 79 ± 12.9 mL minute^⁻1 kg^⁻1 and 1125 ± 309 mL kg^⁻1. The t_1/2 was 26.7 ± 9.25 minutes for H-IM. Area under the curve was 518 ± 87.5 and 1128 ± 810 minute ng mL^⁻1 for H-IV and H-IM, respectively. The IM bioavailability was 217%. The overall thermal thresholds for both H-IV and H-IM were significantly greater than P (p < 0.0001 for both) and baseline (p = 0.006). There was no difference in thermal threshold between H-IV and H-IM. No difference was found in physical examination variables among groups or in comparison to baseline. Fecal weight was significantly less than P for H-IV and H-IM (p = 0.02).

CONCLUSIONS AND CLINICAL RELEVANCE

IM hydromorphone has high bioavailability and provides a similar degree of antinociception to IV administration. IM hydromorphone in horses provides a similar degree and duration of antinociception to IV administration.

Impact of thoracic paravertebral block combined with general anesthesia on postoperative cognitive function and serum adiponectin levels in elderly patients undergoing lobectomy

Introduction

Thoracic paravertebral block (TPVB) can improve postoperative analgesia, inhibiting perioperative stress and the inflammatory response. However, whether it can improve early postoperative cognitive dysfunction (POCD) by altering the secretion and expression of serum ADP remains unclear.

Aim

To investigate the impact of thoracic paravertebral block combined with general anesthesia (TPVB-GA) on postoperative cognitive function and serum adiponectin (ADP) levels in elderly patients undergoing lobectomy.

Material and methods

A total of 120 elderly patients undergoing elective lobectomy were randomly divided into three groups: general anesthesia (GA); TPVB-GA (PG); epidural block combined with general anesthesia (EG). Cognitive function in the three groups was evaluated 1 day before and 7 days after surgery. The serum levels of ADP and S-100β protein were evaluated before anesthesia (T0), 15 min after skin incision (T3), and 7 days after surgery (T5).

Results

Cognitive function scores in the three groups decreased by different extents at T5 (p < 0.05); scores in groups PG and EG were higher than those in group GA (p < 0.05). The serum levels of S-100β protein in the three groups at T3 were higher than those at T0 (p < 0.05); however, serum ADP concentrations were reduced (p < 0.05); the serum levels of S-100β protein in groups PG and EG were lower than those in group GA at T3, while serum ADP levels were higher.

Conclusions

Thoracic paravertebral block or epidural block combined with general anesthesia can improve early postoperative cognitive function in elderly patients undergoing lobectomy. TPVB-GA demonstrated better effects, which may be related to the secretion of ADP.

A Clinical Feasible Method for Computed Tomography-Based Assessment of Sarcopenia in Patients With Chronic Pancreatitis

OBJECTIVES

Sarcopenia is a serious but often overlooked complication of chronic pancreatitis (CP). We investigated the prevalence and risk factors for sarcopenia in patients with CP and determined the utility of a computed tomography (CT)-based method, based on psoas muscle measurements, for easy and clinical feasible diagnosis of sarcopenia.

METHODS

This was a retrospective multicenter study of 265 patients with CP. We used segmentation of CT images to quantify skeletal muscle mass and diagnose sarcopenia. On the same CT image as used for muscle segmentation, psoas muscle thickness and cross-sectional area were measured and receiver operating characteristic analyses defined age and sex-specific cutoffs for diagnosing sarcopenia.

RESULTS

The prevalence of sarcopenia was 20.4%. The optimal height-adjusted psoas muscle cross-sectional area cutoff for diagnosing sarcopenia was 3.3 cm/m in males and 2.5 cm/m in females. The corresponding area under the receiver operating characteristic curves were 0.8 and 0.9, with sensitivities of 84% and 81% and specificities of 62% and 81%, respectively. Comparable diagnostic performance characteristics were observed for psoas muscle thickness.

CONCLUSIONS

Sarcopenia is present in 1 of 5 patients with CP. Assessment of psoas muscle parameters provides a clinical feasible method to diagnose sarcopenia.

Effects of Naloxegol on Gastrointestinal Transit and Colonic Fecal Volume in Healthy Participants Receiving Oxycodone

Background/Aims

Opioids cause gastrointestinal (GI) dysmotility, decrease gut secretion, and affect gut sphincters. Symptoms of opioid-induced bowel dysfunction may be alleviated by peripherally acting opioid antagonists like naloxegol, but detailed knowledge on GI effects of this drug is lacking. We hypothesized that naloxegol, compared to placebo, would reduce GI transit time and colonic fecal volume in opioid-treated healthy participants.

Methods

We conducted a randomized, double-blinded, single-center, 2-way cross-over study in 24 healthy males, randomized to a 6 day treatment period of oxycodone (15 mg twice a day) co-administered with either naloxegol (25 mg once a day) or matching placebo. Participants swallowed an electromagnetic capsule which determined GI transit times. Colonic fecal volume was quantified with magnetic resonance imaging both pre-treatment and post-treatment.

Results

Naloxegol reduced total GI transit time by 21% (56 hours vs 71 hours, P = 0.02) and colonic transit time by 23% (45 hours vs 59 hours, P < 0.01), compared to placebo. However, no difference in colonic fecal volume was found (818 mL vs 884 mL, P = 0.20).

Conclusions

Short-term administration of naloxegol in healthy participants reverses the retardation of total GI and colonic transit induced by oxycodone. This supports the use of naloxegol in the treatment of GI side effects to opioid treatment, and add knowledge to the current understanding of mechanisms behind peripherally-acting opioid antagonists.

Roux Limb Motility in Gastric Bypass Patients with Chronic Abdominal Pain-Is There an Association to Prescribed Opioids?

BACKGROUND/AIM

A number of patients continue to suffer from chronic abdominal pain of unknown origin, which may also lead to a prolonged use of opioid analgesics. Symptoms of abdominal pain, nausea and vomiting in this patient group resemble the characteristics of the Roux stasis Syndrome. The aim was to elucidate relationships between chronic abdominal pain, Roux limb motor activity and opioid analgesics.

METHODS

Roux limb high-resolution manometry and ratings of abdominal pain and quality of life were analysed in 15 gastric bypass patients reporting abdominal pain of unknown origin. Effect of acute opiate administration (morphine i.v.) on fasting Roux limb motor activity was assessed in asymptomatic and morphine-naïve gastric bypass patients (n = 9) and compared with an untreated control group (n = 11).

RESULTS

In the symptomatic patient group, we found disturbed Roux limb motor patterns in 10 out of 15 examinations, but no signs of Roux stasis syndrome. A high prevalence of prescribed opioid analgesics as well as a high number of reoperations in this group. The worst quality of life and the highest number of pain-killing medications were observed among the patients with distal pacemaker activity in Roux limb. In the morphine-naïve and asymptomatic patients, morphine increased the muscular tone in the Roux limb during phase III-like motor activity. A majority of the RYGBP patients with chronic abdominal pain had a disturbed Roux limb fasting motility, and there was a high prevalence of prescribed opioid analgesics. In opiate-naïve RYGBP patients, acute morphine intravenously increased the muscular tone of the Roux limb.