Investigational opioid antagonists for treating opioid-induced bowel dysfunction

An update on the use of pharmacotherapy for opioid-induced bowel dysfunction

INTRODUCTION

With the growing rate of aging and the incidence of chronic diseases, there has been an upsurge in opioid prescription and abuse worldwide. This has been associated with increased reports of opioid-related adverse events, particularly opioid-induced bowel dysfunction (OIBD), calling for a rational clinical management strategy.

AREAS COVERED

Through searching PubMed, Scopus, Cochrane Library, and Web of Science, English literature was gathered as of 1 January 2017. Furthermore, the USFDA, EMA, TGA, Clinicaltrials.Gov, WHO-ICTRP databases, and the latest guidelines were reviewed to extract ongoing clinical studies and provide an evidence-based expert opinion with detailed information on efficacy, safety, approval status, and pharmacokinetics of the currently used medications.

EXPERT OPINION

Despite the significant burden of OIBD, the clinical development of agents lags behind disease progress. Although in most places, management of opioid-induced constipation (OIC) is initiated by lifestyle modifications followed by laxatives, opioid antagonists, and secretagogue agents, there are still major conflicts among global guidelines. The fundamental reason is the lack of head-to-head clinical trials providing inter- and intragroup comparisons between PAMORAs, laxatives, and secretagogue agents. These investigations must be accompanied by further valid biopharmaceutical and economic evaluations, paving the way for rational clinical judgment in each context.

Intravenous lidocaine simultaneously infused with sufentanil to accelerate gastrointestinal function recovery in patients after thoracolumbar surgery: a prospective, randomized, double-blind controlled study

PURPOSE

Postoperative gastrointestinal dysfunction is one of the common complications of surgery, especially after surgery for a thoracolumbar spinal fracture. Intravenous lidocaine is a potential method to improve postoperative gastrointestinal function in surgical patients, reduce opioid use and shorten hospital stays. The purpose of this study is to explore the effect of intravenous lidocaine on the recovery of gastrointestinal function in patients after thoracolumbar surgery.

METHODS

In this study, 48 eligible patients undergoing elective thoracolumbar spine fractures resection and internal fixation surgery were enrolled to receive intravenous injections of lidocaine in different concentrations during the perioperative period. Patients were randomly divided into three groups: control group (group A), low concentration of lidocaine group (group B) and high concentration of lidocaine group (group C), 16 patients in each group. First postoperative exhaust time, numbers of bowel sound at preoperative and postoperative 3, 6, 12, 24 h, pain scores at postoperative 0, 3, 6, 12, 24, 48 h, total sufentanil use in PACU and perioperative periods, postoperative hospital stay and analgesic remedy within postoperative 48 h were recorded and compared. The primary endpoints include: the time of first flatus passage after the operation, the number of bowel sounds per minute counted with stethoscope at 30 min before anesthesia induction and at 3, 6, 12 and 24 h postoperative. The secondary endpoints included: the pain scores at PACU (after entering into PACU), 3, 6, 12, 24 and 48 h postoperative, the amount of sufentanil administrated by intravenous push during operation and the numbers of patients needed rescuing sufentanil in PACU, and the numbers of patients needed administration of gastric motility drugs or non-steroidal analgesics at ward within 48 h postoperation, length of hospital stay (from the first day after surgery to discharge from hospital) and the incidence of adverse reactions.

RESULTS

Compared with group A, the first postoperative exhaust time in group B and C occurred much earlier (23.3 ± 11.0 h vs. 16.0 ± 6.6 h, 16.6 ± 5.1 h, P < 0.05). Compared with preoperation, the numbers of bowel sound significantly increased at 24 h postoperatively in group B, while group B at 6 h and group C at 6 and 24 h postoperatively had significantly more active bowel sounds compared to group A (P < 0.05). There were no remarkable differences in VAS scores within 12 h postoperatively among three groups, and however, significantly lower VAS scores were found at 12, 24 and 48 h postoperatively in group C when comparing to Group A (p < 0.05). There was no statistical significance in the incidence of postoperative flatulence and nausea and vomiting, the number of patients needed rescuing sufentanil in PACU, the length of postoperative hospital stay and the number of patients requiring non-steroidal analgesics at ward within 48 h postoperation.

CONCLUSIONS

Intravenous lidocaine infusion together with patient-controlled analgesia of sufentanil expedited the early recovery of gastrointestinal function and improved analgesic quality of sefentanyl in patients undergoing thoracolumbar surgeries.

P2Y1 receptor in the colonic submucosa of rats and its association with opioid‑induced constipation

The aim of the present study was to explore the expression changes of P2Y purinergic receptor 1 (P2Y1) in the distal colonic submucosa of opioid-induced constipation (OIC) rats and its association with the occurrence of OIC, an OIC rat model was generated by intraperitoneal injection of loperamide hydrochloride, a selective agonist of µ-opioid receptors (MORs). At 7 days post-treatment, the model was assessed by analyzing stool scores and calculating the gastrointestinal (GI) transit ratio of rats. The distribution of P2Y1-expressing neurons in the colonic submucosal plexus was demonstrated by immunofluorescence (IF). Western blotting was performed to evaluate the expression changes of MOR, P2Y1 and ATP synthase subunit β (ATPB) proteins in the colonic submucosa, while reverse transcription-quantitative PCR (RT-qPCR) analysis was performed to determine the relative mRNA expression of MOR and P2Y1. After 7 days, the feces of OIC rats exhibited an appearance of sausage-shaped pieces and both the stool weight and GI transit ratio of OIC rats were significantly decreased. IF revealed co-expression of P2Y1 and calbindin and MOR and ATPB in the nerve cells of the distal colonic submucosal plexus. Moreover, RT-qPCR analysis showed that the MOR mRNA levels were significantly increased in the distal colonic submucosa of OIC rats, while mRNA levels of P2Y1 were decreased. WB showed that in the distal colonic submucosa of OIC rats, MOR protein expression was increased, whereas that of P2Y1 was significantly decreased. GI transit ratio analysis suggested that the P2Y agonist ATP significantly relieved constipation symptoms in rats, while the P2Y inhibitor MRS2179 aggravated these symptoms. Finally, P2Y1 expression change was shown to be associated with the occurrence of OIC, while expression of MOR and P2Y1 was associated with OIC development in rats.

Peripherally acting opioid analgesics and peripherally-induced analgesia

The management of pain, particularly chronic pain, is still an area of medical need. In this context, opioids remain a gold standard for the treatment of pain. However, significant side effects, mainly of central origin, limit their clinical use. Here, we review recent progress to improve the therapeutic and safety profiles of opioids for pain management. Characterization of peripheral opioid-mediated pain mechanisms have been a key component of this process. Several studies identified peripheral µ, δ, and κ opioid receptors (MOR, DOR, and KOR, respectively) and nociceptin/orphanin FQ (NOP) receptors as significant players of opioid-mediated antinociception, able to achieve clinically significant effects independently of any central action. Following this, particularly from a medicinal chemistry point of view, main efforts have been directed towards the peripheralization of opioid receptor agonists with the objective of optimizing receptor activity and minimizing central exposure and the associated undesired effects. These activities have allowed the characterization of a great variety of compounds and investigational drugs that show low central nervous system (CNS) penetration (and therefore a reduced side effect profile) yet maintaining the desired opioid-related peripheral antinociceptive activity. These include highly hydrophilic/amphiphilic and massive molecules unable to easily cross lipid membranes, substrates of glycoprotein P (a extrusion pump that avoids CNS penetration), nanocarriers that release the analgesic agent at the site of inflammation and pain, and pH-sensitive opioid agonists that selectively activate at those sites (and represent a new pharmacodynamic paradigm). Hopefully, patients with pain will benefit soon from the incorporation of these new entities.

Opioid-induced bowel dysfunction: suggestions from a multidisciplinary expert Board

Constipation, one of the adverse effects of opioid therapy with a major impact on quality of life, is still an unmet need for cancer patients, particularly those with an advanced and progressive disease, and for non-cancer patients chronically treated with opioids. The awareness of this condition is poor among healthcare providers, despite the recent publication of guidelines and consensus conferences. An early multidisciplinary approach of opioid-induced bowel dysfunction (OIBD), based on available therapies of proven effectiveness, could support clinicians in managing this condition, thus increasing patients’ adherence to pain therapy. Several Italian experts involved in the management of patients suffering from pain (anaesthesia pain therapy, oncology, haematology, palliative care, gastroenterology) joined in a Board in order to draw up an expert opinion on OIBD. The most frequent and still unsolved issues in this field were examined, including a more comprehensive definition of OIBD, the benefits of early intervention to prevent its occurrence and the most appropriate use of peripherally acting mu-opioid receptor antagonists (PAMORAs). The use of the recently introduced PAMORA naloxegol was analysed, in light of the current literature. The Board proposed a solution for each open issue in the form of recommendations, integrated with the contribution of representatives from different disciplines and often accompanied by procedural algorithms immediately usable and applicable in daily clinical practice. Safety and quality of life of the patient suffering from pain and from the adverse effects of pain therapies have been the mainstays of this expert opinion, in cooperation with general practitioners and caregivers.