Benefit-Risk Analysis of Buprenorphine for Pain Management

Strategy for effective analgesia with intravenous buprenorphine in patients with acute postoperative pain

BACKGROUND

Analgesic treatment is the primary method for managing acute postoperative pain. Opioid analgesics are the main class of drugs used to treat moderate to severe pain, whether it is acute or chronic. These opioids differ in various ways, including their pharmacochemical properties, distribution and absorption rates, metabolism, and elimination pathways for the drug and its metabolites. These differences result in varying degrees of analgesic efficacy, which, in clinical practice, allows for the selection of the most effective drug that maximizes pain relief while ensuring safety. Buprenorphine is a semi-synthetic opioid with properties that are not yet fully understood. It has a wide range of applications in treating both acute and chronic pain, including non-cancer and cancer-related pain. One of the most significant clinical advantages of buprenorphine is its safety profile, which includes a ceiling effect on respiratory depression, no immunosuppressive effects, inhibition of hyperalgesia, no cumulative effects in patients with renal failure, and a low risk of constipation following its use.

AIM

This study aims to analyze current reports on the use of intravenous buprenorphine as a first-line opioid analgesic for postoperative pain relief. The paper discusses the pharmacochemical properties of the drug and the mechanisms behind postoperative pain. Additionally, it presents the experiences of the pain management team at Copernicus Hospital in Gdansk regarding administering intravenous buprenorphine.

MATERIAL AND METHODS

The current literature on buprenorphine for treating moderate to severe acute pain has been reviewed, focusing on its effectiveness in managing postoperative pain following surgical procedures. Additionally, the experience of the Copernicus Hospital pain team with buprenorphine is summarized in a brief discussion.

CONCLUSION

After reviewing current literature and recommendations, along with the experiences of the pain management team at Copernicus Hospital in Gdańsk, it can be concluded that buprenorphine is an analgesic that demonstrates a high level of efficacy and safety. When used in combination with non-opioid analgesics, buprenorphine achieves a synergistic effect, resulting in effective pain relief. This approach facilitates early patient rehabilitation and enables a swift return to normal activities, even following extensive surgical procedures.

Unrestricted insurance coverage of buprenorphine formulations remains sparse in comparison to conventional opioids

OBJECTIVE

Buprenorphine is an atypical opioid with analgesic efficacy and a more favorable safety profile than conventional opioids or tramadol. In 2019, access to on-label buprenorphine formulations was limited in comparison to conventional opioids, despite evidence supporting buprenorphine's first-line analgesic use. Considering recent policy changes increasing buprenorphine accessibility, we determined differences in unrestricted insurance coverage between buprenorphine, conventional opioids, and other atypical opioids.

METHODS

We used data from Managed Market Insights and Technology's Coverage Search and Kaiser Family Foundation to generate estimates on percentages of US-covered lives with unrestricted access to oxycodone, morphine, tramadol, tapentadol, generic and on-label transdermal buprenorphine, on-label buccal buprenorphine, and on-label sublingual buprenorphine/naloxone in 2024.

RESULTS

79.7% of commercial and 99.1% of Medicare lives had unrestricted oxycodone access. Morphine access was unrestricted for 45.7% of commercial and 62.8% of Medicare lives. Unrestricted access to tramadol was available for 88.2% of commercial and 96.3% of Medicare lives. 37.3% of commercial and 10.1% of Medicare lives had unrestricted tapentadol access. Unrestricted access to on-label transdermal buprenorphine was available for 21.0% of commercial and 2.59% of Medicare lives. Generic transdermal buprenorphine was available for 52.1% of commercial and 30.0% of Medicare lives. Buccal buprenorphine was available without restriction for 52.7% of commercial and 19.8% of Medicare lives. Sublingual buprenorphine/naloxone had unrestricted coverage for 34.6% of commercial and 32.7% of Medicare lives.

CONCLUSIONS

Access to buprenorphine formulations was limited in comparison to other opioids. This study emphasizes a need for commercial and Medicare health insurance plans to broaden buprenorphine coverage.

Perioperative Medicine for Ambulatory Surgery

Ambulatory anesthesia for same-day surgery is a fast-growing and ever-improving branch of modern anesthesia. This is primarily driven by the involvement of anesthesiologists as perioperative physicians working in multidisciplinary groups. These groups work together to improve patient safety, patient outcomes, and overall efficiency of both in-patient and out-patient surgery. Appropriate patient selection and optimization are critical to maintain and improve the foundational entities of best ambulatory anesthesia practice. In this review article, a selection of considerations in the field of ambulatory anesthesia are featured, such as the aging population, sleep apnea, obesity, diabetes, cardiac disease, substance abuse, preoperative medication management, multimodal analgesia, social determinants of health, and surgical facility resources.

Pharmacological Pain Treatment in Older Persons

Pharmacological pain treatment in older persons is presented by a multi-disciplinary group of European pain experts. Drugs recommended for acute or chronic nociceptive pain, also for neuropathic pain and the routes of administration of choice are the same as those prescribed for younger persons but comorbidities and polypharmacy in older persons increase the risk of adverse effects and drug interactions. Not all drugs are available or authorised in all European countries. For mild-to-moderate pain, non-opioids including paracetamol and non-steroidal anti-inflammatory drugs are first-line treatments, followed by nefopam and metamizole. Codeine, dihydrocodeine and tramadol are prescribed for moderate to severe pain and 'strong' opioids, including morphine, hydromorphone, oxycodone, fentanyl, buprenorphine, methadone and tapentadol, for severe pain. Chronic neuropathic pain treatment relies on coanalgesics, including anti-epileptics (gabapentinoids) and anti-depressants with additional option of topical lidocaine and capsaicine. The choice of analgesic(s) and the route of administration should be guided by the pain characteristics, as well as by the patient's comorbidities, organ function and medications. Several directions have been highlighted to optimise pharmacological pain management in older individuals: (1) before starting pain treatment adequately detect and assess pain and always perform a full geriatric assessment, (2) consider kidney function systematically to adjust the doses of analgesics and avoid the risks of overdose, (3) start with the lowest dose of an analgesic and increase it gradually under the control of the effect, (4) involve the older persons and family in their treatment, (5) reevaluate pain regularly during treatment and (6) combine pharmacological treatment with non-pharmacological approaches.

Buprenorphine: An anesthesia-centric review

Buprenorphine was synthesized in the 1960s as a result of a search for a safe and effective opioid analgesic. Present formulations of buprenorphine are approved for the treatment of both acute and chronic pain. Its long duration of action, high affinity, and partial agonism at the µ-opioid receptor have established it as a mainstay treatment for opioid use disorder (OUD). Full agonist opioids (FAOs) remain a primary choice for perioperative pain in both opioid-naïve and opioid-tolerant patients despite well-known harms and new emphasis on multimodal analgesia strategies prioritizing nonopioid analgesics. We review the evidence supporting the use of buprenorphine as an effective analgesic alternative to more commonly prescribed FAOs in acute and chronic pain management. For the patient prescribed buprenorphine for OUD, prior conventionalism advised temporary discontinuation of buprenorphine preoperatively; this paradigm has shifted toward continuing buprenorphine throughout the perioperative period. Questions remain whether dose adjustments may improve patient outcomes.

Pain in people seeking and receiving opioid agonist treatment: A systematic review and meta-analysis of prevalence and correlates

BACKGROUND AND AIMS

People with opioid use disorder (OUD) commonly experience pain including chronic pain. Despite the high prevalence, few studies have systematically examined the prevalence and correlates of pain among people seeking or receiving opioid agonist treatment (OAT) for OUD. This review aimed to determine the prevalence of pain in this population globally, and estimate the association between chronic pain and other demographic and clinical characteristics.

METHODS

Electronic searches were conducted in three databases (Medline, Embase and PsycINFO) from the inception until October 2022. Eligible studies reported prevalence rates of current and/or chronic pain. Meta-analyses examining the main prevalence estimates were conducted by Stata SE 18.0, and comorbid clinical conditions were analysed by Review Manager 5.4.

RESULTS

Fifty-six studies (n participants = 35 267) from sixty-seven publications were included. Prevalence estimates of current and chronic pain were reported in 27 (48.2%) and 40 studies (71.4%), respectively. Most studies were conducted in North America (71.4%, n = 40) and used cross-sectional designs (64.3%, n = 36). Meta-analyses revealed a pooled prevalence of 60.0% (95% confidence interval [CI]: 52.0-68.0) for current pain and 44.0% [95% CI: 40.0-49.0] for chronic pain. Chronic pain was positively associated with older age (mean deviation of mean age: 2.39 years, 95% CI: 1.40-3.37; I2 = 43%), unemployment (odds ratio [OR] = 0.57, 95% CI: 0.42-0.76; I2 = 78%), more severe mental health symptoms (e.g. more severe depression (standardised mean difference [SMD] of mean scores: 0.45, 95% CI: 0.20-0.70; I2 = 48%) and anxiety symptoms (SMD: 0.52, 95% CI: 0.17-0.88; I2 = 67%), and hepatitis C (OR = 1.41, 95% CI: 1.03-1.94; I2 = 0%). No association was observed between chronic pain and the onset and type of OAT, geographic location, study design, survey year, participant age or use of specific pain assessment tools.

CONCLUSIONS

There appears to be a high prevalence of pain among people seeking or receiving opioid agonist treatment for opioid use disorder compared with the general population, with positive associations for older age, unemployment, hepatitis C and the severity of some mental health symptoms.

Low-Efficacy Mu Opioid Agonists as Candidate Analgesics: Effects of Novel C-9 Substituted Phenylmorphans on Pain-Depressed Behavior in Mice

Low-efficacy mu opioid receptor (MOR) agonists may serve as novel candidate analgesics with improved safety relative to high-efficacy opioids. This study used a recently validated assay of pain-depressed behavior in mice to evaluate a novel series of MOR-selective C9-substituted phenylmorphan opioids with graded MOR efficacies. Intraperitoneal injection of dilute lactic acid (IP acid) served as a noxious stimulus to depress locomotor activity by mice in an activity chamber composed of two compartments connected by an obstructed door. Behavioral measures included (1) crosses between compartments (vertical activity over the obstruction) and (2) movement counts quantified as photobeam breaks summed across compartments (horizontal activity). Each drug was tested alone and as a pretreatment to IP acid. A charcoal-meal test and whole-body-plethysmography assessment of breathing in 5% CO2 were also used to assess gastrointestinal (GI) inhibition and respiratory depression, respectively. IP acid produced a concentration-dependent depression in crosses and movement that was optimally alleviated by intermediate- to low-efficacy phenylmorphans with sufficient efficacy to produce analgesia with minimal locomotor disruption. Follow-up studies with two low-efficacy phenylmorphans (JL-2-39 and DC-1-76.1) indicated that both drugs produced naltrexone-reversible antinociception with a rapid onset and a duration of ∼1 h. Potency of both drugs increased when behavior was depressed by a lower IP-acid concentration, and neither drug alleviated behavioral depression by a non-pain stimulus (IP lithium chloride). Both drugs produced weaker GI inhibition and respiratory depression than fentanyl and attenuated fentanyl-induced GI inhibition and respiratory depression. Results support further consideration of selective, low-efficacy MOR agonists as candidate analgesics. SIGNIFICANCE STATEMENT: This study used a novel set of mu opioid receptor (MOR)-selective opioids with graded MOR efficacies to examine the lower boundary of MOR efficacy sufficient to relieve pain-related behavioral depression in mice. Two novel low-efficacy opioids (JL-2-39, DC-1-76.1) produced effective antinociception with improved safety relative to higher- or lower-efficacy opioids, and results support further consideration of these and other low-efficacy opioids as candidate analgesics.

Efficacy and safety of sublingual buprenorphine in managing acute postoperative pain - A systematic review

Sublingual (SL) buprenorphine has been used as a modality of managing acute postoperative pain in many studies. This systematic review aimed to investigate the safety and efficacy of SL buprenorphine as an analgesic for various surgeries. After registering the protocol with PROSPERO, we searched PubMed, Cochrane Library, and Ovid databases with relevant keywords. The primary outcomes were 24-hour pain scores, and the secondary outcomes were postoperative nausea and vomiting, sedation scores, pruritus, rescue analgesia, and urinary retention. The risk of bias scale was used to identify the quality of evidence. From the 103 articles identified, four randomized-controlled trials fulfilled the inclusion criteria for qualitative analysis. The overall risk of bias was low. Most of the studies showed that the use of SL buprenorphine led to either better or comparable pain scores when compared to a control group with lesser or tolerable adverse events. There was a lot of heterogeneity across the studies in this systematic review in terms of the type of surgery performed, the comparison groups, doses of buprenorphine, and the outcomes that were assessed. Therefore, a quantitative meta-analysis was not performed. The results of this systematic review should be interpreted with caution due to heterogeneity in the methodology. Adequately powered studies with robust methodology should investigate the safety and efficacy of SL buprenorphine when used for postoperative analgesia.

Multimodal postoperative analgesia with transdermal buprenorphine is a safe option in arthroscopic rotator cuff repair

BACKGROUND

Arthroscopic rotator cuff repairs are associated with moderate-to-severe pain. Opioids are not the first line for postsurgical pain control due to their potential misuse and side effects. Transdermal buprenorphine represents an alternative for multimodal postoperative pain control.

METHODS

This was a single-centre, prospective longitudinal exploratory study of patients undergoing arthroscopic rotator cuff repairs managed with multimodal analgesia with transdermal buprenorphine. Patients were followed-up by telephone at eight time points, assessing pain levels, rescue analgesics requirement and side effects.

FINDINGS

Twenty-five patients with an average age of 63.4 ± 8.2 were included. Fourteen patients were ⩾65 years. Pain levels were similar among age groups at all time points, with no pain or mild pain (visual analogue scale 1-4) in most patients. The most frequent side effects were dizziness and somnolence.

CONCLUSION

Transdermal buprenorphine provided a sustained analgesic effect after an arthroscopic rotator cuff repair during the acute postsurgical period. It showed a similar safety profile among younger and older patients.

Recent Update on Pretreatment and Analysis Methods of Buprenorphine in Different Matrix

Buprenorphine is one of the most commonly used pain-killing drugs due to its lengthy duration of action and high potency. However, excessive usage of buprenorphine can be harmful to one's health and prolonged use might result in addiction. Additionally, an increasing number of cases have been documented involving the illegal use of buprenorphine. Therefore, a variety of effective and reliable methods for pretreatment and determination of buprenorphine and its main metabolite norbuprenorphine have been established. This review aims to update the current state of pretreatment and detection techniques for buprenorphine and norbuprenorphine from January 2010 to March 2022. Pretreatment methods include several traditional extraction methods, solid-phase extraction, QuECHERS, various micro-extraction techniques, etc. while analytical methods include LC-MS, LC coupled with other detectors, GC-MS, capillary electrophoresis, electrochemical sensors, etc. The pros and cons of various techniques were compared and summarized, and the prospects were provided.HIGHLIGHTSProgress in pretreatment and detection methods for buprenorphine is demonstrated.Pros and cons of different pretreatment and analysis methods are compared.New materials (such as nanomaterials and magnetic materials) used in buprenorphine pretreatment are summarized.Newly emerged environmental-friendly methods are discussed.

Economic burden and dosing trends of buprenorphine buccal film and transdermal patch in chronic low back pain

Aim: Exploring prescribing trends and economic burden of chronic low back pain (cLBP) patients prescribed buprenorphine buccal film (Belbuca®) or transdermal patches. Methods: In the MarketScan® commercial insurance claims (employees and their spouses/dependents, 2018-2021), the first film or patch prescription date was an index event. The observation covered 6-month pre-index and 12-month post-index periods. Results: Patients were propensity-score matched (708 per cohort). Buprenorphine initiation had stable cost trends in buccal film and increasing trends in transdermal patch cohort. Between-cohort comparisons of healthcare expenditures, cost trends and resource utilization showed significant differences, mostly in favor of buccal film. Buccal film also had higher daily doses and wider dosing range. Conclusion: Buprenorphine film is more cost-effective cLBP treatment with more flexible dosing.

Development and Validation of a Treatment Algorithm for Osteoarthritis Pain Management in Patients With End-Stage Kidney Disease Undergoing Hemodialysis

Background

Although osteoarthritis is common in the hemodialysis population and leads to poor health outcomes, pain management is challenged by the absence of clinical guidance. A treatment algorithm was developed and validated to aid hemodialysis clinicians in managing osteoarthritis pain.

Objective

The objective was to develop and validate a treatment algorithm for managing osteoarthritis pain in patients undergoing hemodialysis.

Design

A validation study was conducted based on Lynn's method for content validation.

Setting

To develop and validate a treatment algorithm, interviews were conducted virtually by the primary researcher with clinicians from various institutions across the Greater Toronto and Hamilton Area in Ontario.

Patients

The treatment algorithm was developed and validated for the management of osteoarthritis pain in patients on hemodialysis. Patients were not involved in the development or validation of the tool.

Measurements

The algorithm was measured for content and face validity. Content validity was measured by calculating the content validity index of each component (I-CVI) of the algorithm and the overall scale validity index (S-CVI). Face validity was assessed by calculating the percentage of positive responses to the face validity statements.

Methods

A draft algorithm was developed based on literature searches and expert opinion and validated by interviewing nephrology and pain management clinicians. Through consecutive rounds of 1:1 interviews, content and face validity were assessed by asking participants to rate the relevance of each component of the algorithm and indicate their level of agreeability with a series of statements. Following each round, the I-CVI of the algorithm as well as the S-CVI was calculated and the percentage of positive responses to the statements was determined. The research team revised the algorithm in response to the findings. The final algorithm provides a stepwise approach to the non-pharmacologic and pharmacologic management of pain, including topical, oral, and opioid use.

Results

A total of 18 clinicians from 7 institutions across the Greater Toronto and Hamilton Area were interviewed (10 pharmacists, 5 nurse practitioners, and 3 physicians). The average S-CVI of the algorithm across all 3 rounds was 0.93. At least 78% of participants provided positive responses to the face validity statements.

Limitations

An algorithm was developed based on input from clinicians working in the province of Ontario, limiting the generalizability of the algorithm across provinces. In addition, the algorithm did not include the perspectives of primary care providers or patients/caregivers.

Conclusions

An algorithm for the management of osteoarthritis pain in the hemodialysis population was developed and validated through expert review to standardize practices and encourage clinicians to use evidence-based treatments and address the psychosocial symptoms of pain. As the algorithm possesses a high degree of content and face validity, it may improve osteoarthritis pain management among patients undergoing hemodialysis. Future research will assess the implementation of the algorithm across hemodialysis settings.

Buprenorphine Facilitates Rapid Weaning From Very-High-Dose Intrathecal Hydromorphone

Pain management in patients on chronic opioid therapy is a common clinical challenge. The phenomena of opioid-induced hyperalgesia and tolerance are important contributors to that challenge. There are multiple strategies described to wean opioid doses and/or transition patients off opioids altogether. However, there is very little data to guide transitions off chronic intrathecal opioids. Here, we report on two patients with intractable post-laminectomy pain syndrome, resulting in severe functional limitation in the setting of opioid escalation culminating in the intrathecal delivery of hydromorphone to daily doses as high as 20 mg/day. We describe their rapid successful weaning off opioids using low-dose buprenorphine, which resulted in a dramatic improvement in pain and function.

Frontline Perspectives on Buprenorphine for the Management of Chronic Pain

Due to the prevalence of chronic pain and high-impact chronic pain in the US, a significant percentage of the population is prescribed opioids for pain management. However, opioid use disorder is associated with reduced quality of life, along with fatal opioid overdoses, and is a significant burden on the US economy. Considering the clinical needs of patients with intractable chronic pain and the potential harms associated with prescribed and illicit opioids in our communities, having a deep understanding of current treatment options, supporting evidence, and clinical practice guidelines is essential for optimizing treatment selections. Buprenorphine is a Schedule III opioid with a unique mechanism of action, allowing effective and long-lasting analgesia at microgram doses with fewer negative side effects and adverse events, including respiratory depression, when compared with other immediate-release, long-acting, and extended-release prescription opioids. Due to its relatively lower risk for overdose and misuse, buprenorphine was recently added to the Clinical Practice Guideline for the Use of Opioids in the Management of Chronic Pain as a first-line treatment for chronic pain managed by opioids by the US Departments of Defense and Veterans Affairs, and the Department of Health and Human Services recommends that buprenorphine be made available for the treatment of chronic pain. In this narrative review, we discuss the different buprenorphine formulations, clinical efficacy, advantages for older adults and other special populations, clinical practice guideline recommendations, and payer considerations of buprenorphine and suggest that buprenorphine products approved for chronic pain should be considered as a first-line treatment for this indication.

Buprenorphine for Chronic Pain Management: a Narrative Review

PURPOSE OF REVIEW

The aim of this review is to educate healthcare professionals regarding buprenorphine for the use of opioid use disorder (OUD) as well as for chronic pain management. This review provides physicians and practitioners with updated information regarding the distinct characteristics and intricacies of prescribing buprenorphine.

RECENT FINDINGS

Buprenorphine is approved by the US Food and Drug Administration (FDA) for acute pain, chronic pain, opioid use disorder (OUD), and opioid dependence. When compared to most other opioids, buprenorphine offers superior patient tolerability, an excellent half-life, and minimal respiratory depression. Buprenorphine does have notable side effects as well as pharmacokinetic properties that require special attention, especially if patients require future surgical interventions. Many physicians are not trained to initiate or manage patients on buprenorphine. However, buprenorphine offers a potentially safer alternative for medication management for patients who require chronic opioid therapy for pain or have OUD. This review provides updated information on buprenorphine for both chronic pain and OUD.

Outpatient cross-titration to buprenorphine for chronic pain: A retrospective analysis

OBJECTIVE

To determine the effectiveness and safety of the University of Washington's buprenorphine cross-titration protocol for chronic pain in the outpatient setting.

METHODS

Retrospective chart review was performed on 150 patients transitioned from full µ-opioid agonist therapy to buprenorphine using the University of Washington Medical Center Pain Clinic's cross-titration protocol between September 1, 2020, and December 31, 2021, in an outpatient setting. Primary outcome was to determine the percentage of patients who completed the cross-titration and continued buprenorphine without full µ-opioid agonists 4 weeks after completion. Secondary outcomes included final buprenorphine dose, days needed to complete cross-titration, deviation rates from the protocol, and opioid-related adverse events.

RESULTS

Fifteen of 31 (48.4 percent) included patients successfully converted to buprenorphine. Median duration of successful cross-titration was 29 days (interquartile range 19-57). Average end-titration dose for patients on buprenorphine/naloxone sublingual films was 7.9 ± 5.7 mg/day, while for buprenorphine transdermal (TD) patches, it was 11.9 ± 4.8 mcg/h. Morphine equivalent daily dose (MEDD) prior to induction varied widely. All patients transitioned to TD buprenorphine were taking ≤30 mg MEDD. Patients previously taking >120 mg MEDD stabilized on 8-16 mg/day buprenorphine. Most common reasons for cross-titration failure were inadequate pain control and intolerable adverse effects.

DISCUSSION

The University of Washington's buprenorphine cross-titration protocol for chronic pain was successful in about half of included patients undergoing conversion from chronic full µ-opioid agonist therapy and generally well tolerated. Clinical responses were widely variable, and many required slower taper and higher end-titration buprenorphine dose than anticipated. Although protocols provide structure for cross-titration, each course should be monitored closely and individualized.

An Examination of the Complex Pharmacological Properties of the Non-Selective Opioid Modulator Buprenorphine

The goal of this review is to provide a recent examination of the pharmacodynamics as well as pharmacokinetics, misuse potential, toxicology, and prenatal consequences of buprenorphine. Buprenorphine is currently a Schedule III opioid in the US used for opioid-use disorder (OUD) and as an analgesic. Buprenorphine has high affinity for the mu-opioid receptor (MOR), delta (DOR), and kappa (KOR) and intermediate affinity for the nociceptin (NOR). Buprenorphine's active metabolite, norbuprenorphine, crosses the blood-brain barrier, is a potent metabolite that attenuates the analgesic effects of buprenorphine due to binding to NOR, and is responsible for the respiratory depressant effects. The area under the concentration curves are very similar for buprenorphine and norbuprenorphine, which indicates that it is important to consider this metabolite. Crowding sourcing has identified a buprenorphine street value (USD 3.95/mg), indicating some non-medical use. There have also been eleven-thousand reports involving buprenorphine and minors (age < 19) at US poison control centers. Prenatal exposure to clinically relevant dosages in rats produces reductions in myelin and increases in depression-like behavior. In conclusion, the pharmacology of this OUD pharmacotherapy including the consequences of prenatal buprenorphine exposure in humans and experimental animals should continue to be carefully evaluated.

Bispecific sigma-1 receptor antagonism and mu-opioid receptor partial agonism: WLB-73502, an analgesic with improved efficacy and safety profile compared to strong opioids

Opioids are the most effective painkillers, but their benefit-risk balance often hinder their therapeutic use. WLB-73502 is a dual, bispecific compound that binds sigma-1 (S1R) and mu-opioid (MOR) receptors. WLB-73502 is an antagonist at the S1R. It behaved as a partial MOR agonist at the G-protein pathway and produced no/unsignificant β-arrestin-2 recruitment, thus demonstrating low intrinsic efficacy on MOR at both signalling pathways. Despite its partial MOR agonism, WLB-73502 exerted full antinociceptive efficacy, with potency superior to morphine and similar to oxycodone against nociceptive, inflammatory and osteoarthritis pain, and superior to both morphine and oxycodone against neuropathic pain. WLB-73502 crosses the blood-brain barrier and binds brain S1R and MOR to an extent consistent with its antinociceptive effect. Contrary to morphine and oxycodone, tolerance to its antinociceptive effect did not develop after repeated 4-week administration. Also, contrary to opioid comparators, WLB-73502 did not inhibit gastrointestinal transit or respiratory function in rats at doses inducing full efficacy, and it was devoid of proemetic effect (retching and vomiting) in ferrets at potentially effective doses. WLB-73502 benefits from its bivalent S1R antagonist and partial MOR agonist nature to provide an improved antinociceptive and safety profile respect to strong opioid therapy.

Top Ten Tips Palliative Care Clinicians Should Know About Buprenorphine

Pain management in palliative care (PC) is becoming more complex as patients survive longer with life-limiting illnesses and population-wide trends involving opioid misuse become more common in serious illness. Buprenorphine, a generally safe partial mu-opioid receptor agonist, has been shown to be effective for both pain management and opioid use disorder. It is critical that PC clinicians become comfortable with indications for its use, strategies for initiation while understanding risks and benefits. This article, written by a team of PC and addiction-trained specialists, including physicians, nurse practitioners, social workers, and a pharmacist, offers 10 tips to demystify buprenorphine use in serious illness.

Implementation of a peri-operative pain-management algorithm reduces the use of opioid analgesia following pelvic exenteration surgery

AIM

This study aimed to investigate the implementation and pain-related outcomes of a peri-operative pain-management regimen for patients undergoing pelvic exenteration surgery at a university teaching hospital.

METHOD

This is a single-site prospective observational cohort study involving 100 patients who underwent pelvic exenteration surgery between January 2017 and December 2018. A pain-management algorithm regarding the use of opioid-sparing multimodal analgesia was developed between the departments of anaesthesia, pain management and intensive care. The primary outcomes were: compliance with a pain-treatment algorithm compared with a similar retrospective surgical patient cohort in 2013-2014; and requirements for regular doses of opioid analgesia at discharge, measured in oral morphine equivalent daily dose (oMEDD).

RESULTS

Following the introduction of a pain-management algorithm, regional anaesthesia techniques (spinal anaesthesia, transversus abdominus plane block, preperitoneal catheters or epidural analgesia) were used in 83/98 (84.7%) of the 2017-2018 cohort compared with 13/73 (17.8%) of the 2013-2014 cohort (p < 0.001). There was a reduction in the median dose of opioid analgesics (oMEDD) at time of discharge, from 150 mg (interquartile range [IQR]: 75.0-235.0 mg) in the 2013-2014 cohort to 10 mg (IQR: 0.00-45.0 mg) in the 2017-2018 cohort (p < 0.001). There was no change in pain intensity (assessed using the Verbal Numerical Rating Score) or oMEDD in the first 7 days following surgery.

CONCLUSION

Since implementation of a novel peri-operative pain-treatment algorithm, the use of opioid-sparing regional techniques and preperitoneal catheters has increased. Additionally, the dose of opioids required at the time of discharge has reduced significantly.

Identifying Clinically Relevant Drug-Drug Interactions With Methadone and Buprenorphine: A Translational Approach to Signal Detection

Methadone and buprenorphine have pharmacologic properties that are concerning for a high risk of drug-drug interactions (DDIs). We performed high-throughput screening for clinically relevant DDIs with methadone or buprenorphine by combining pharmacoepidemiologic and pharmacokinetic approaches. We conducted pharmacoepidemiologic screening via a series of self-controlled case series studies (SCCS) in Optum claims data from 2000 to 2019. We included persons 18 years or older who experienced an outcome of interest during target drug treatment. Exposures were all overlapping medications (i.e., the candidate precipitants) during target drug treatment. Outcomes were opioid overdose, non-overdose adverse effects, and cardiac arrest. We used conditional Poisson regression to calculate rate ratios, accounting for multiple comparisons with semi-Bayes shrinkage. We explored the impact of key study design choices in analyses that varied the exposure definitions of the target drugs and the candidate precipitant drugs. Pharmacokinetic screening was conducted by incorporating published data on CYP enzyme metabolism into an equation-based static model. In SCCS analysis, 1,432 events were included from 248,069 new users of methadone or buprenorphine. In the primary analysis, statistically significant DDIs included gabapentinoids with either methadone or buprenorphine; baclofen with methadone; and benzodiazepines with methadone. In sensitivity analysis, additional statistically significant DDIs included methocarbamol, quetiapine, or simvastatin with methadone. Pharmacokinetic screening identified two moderate-to-strong potential DDIs (clonidine and fluconazole with buprenorphine). The combination of clonidine and buprenorphine was also associated with a significantly increased risk of opioid overdose in pharmacoepidemiologic screening. These DDI signals may be the most important targets for future confirmation studies.

Buprenorphine and its formulations: a comprehensive review

Buprenorphine, a novel long-acting analgesic, was developed with the intention of two purposes: analgesia and opioid use disorder. Regarding its pharmacodynamics, it is a partial agonist at mu receptors, an inverse agonist at kappa receptors, and an antagonist at delta receptors. For the purpose of analgesia, three formulations of buprenorphine were developed: IV/IM injectable formulation (Buprenex®), transdermal patch formulation (Butrans®), and buccal film formulation (Belbuca®). Related to opioid dependence, the formulations developed were subcutaneous extended release (Sublocade®), subdermal implant (Probuphine®), and sublingual tablets (Subutex®). Lastly, in order to avoid misuse of buprenorphine for opioid dependence, two combination formulations paired with naloxone were developed: film formulation (Suboxone®) and tablet formulation (Zubsolv®). In this review, we present details of each formulation along with their similarities and differences between each other and clinical considerations.

Current and Future Therapeutic Options in Pain Management: Multi-mechanistic Opioids Involving Both MOR and NOP Receptor Activation

Opioids are widely used in chronic pain management, despite major concerns about their risk of adverse events, particularly abuse, misuse, and respiratory depression from overdose. Multi-mechanistic opioids, such as tapentadol and buprenorphine, have been widely studied as a valid alternative to traditional opioids for their safer profile. Special interest was focused on the role of the nociceptin opioid peptide (NOP) receptor in terms of analgesia and improved tolerability. Nociceptin opioid peptide receptor agonists were shown to reinforce the antinociceptive effect of mu opioid receptor (MOR) agonists and modulate some of their adverse effects. Therefore, multi-mechanistic opioids involving both MOR and NOP receptor activation became a major field of pharmaceutical and clinical investigations. Buprenorphine was re-discovered in a new perspective, as an atypical analgesic and as a substitution therapy for opioid use disorders; and buprenorphine derivatives have been tested in animal models of nociceptive and neuropathic pain. Similarly, cebranopadol, a full MOR/NOP receptor agonist, has been clinically evaluated for its potent analgesic efficacy and better tolerability profile, compared with traditional opioids. This review overviews pharmacological mechanisms of the NOP receptor system, including its role in pain management and in the development of opioid tolerance. Clinical data on buprenorphine suggest its role as a safer alternative to traditional opioids, particularly in patients with non-cancer pain; while data on cebranopadol still require phase III study results to approve its introduction on the market. Other bifunctional MOR/NOP receptor ligands, such as BU08028, BU10038, and AT-121, are currently under pharmacological investigations and could represent promising analgesic agents for the future.

Triglyceride-Mimetic Prodrugs of Buprenorphine Enhance Oral Bioavailability via Promotion of Lymphatic Transport

Buprenorphine (BUP) is a potent opioid analgesic that is widely used for severe pain management and opioid replacement therapy. The oral bioavailability of BUP, however, is significantly limited by first-pass metabolism. Previous studies have shown that triglyceride (TG) mimetic prodrugs of the steroid hormone testosterone circumvent first-pass metabolism by directing drug transport through the intestinal lymphatics, bypassing the liver. The current study expanded this prodrug strategy to BUP. Here different self-immolative (SI) linkers were evaluated to conjugate BUP to the 2 position of the TG backbone via the phenol group on BUP. The SI linkers were designed to promote drug release in plasma. Lipolysis of the prodrug in the intestinal tract was examined via incubation with simulated intestinal fluid (SIF), and potential for parent drug liberation in the systemic circulation was evaluated via incubation in rat plasma. Lymphatic transport and bioavailability studies were subsequently conducted in mesenteric lymph duct or carotid artery-cannulated rats, respectively. TG prodrug derivatives were efficiently transported into the lymphatics (up to 45% of the dose in anaesthetised rats, vs. less than 0.1% for BUP). Incorporation of the SI linkers facilitated BUP release from the prodrugs in the plasma and in concert with high lymphatic transport led to a marked enhancement in oral bioavailability (up to 22-fold) compared to BUP alone. These data suggest the potential to develop an orally bioavailable BUP product which may have advantages with respect to patient preference when compared to current sublingual, transdermal patch or parenteral formulations.

Influence of acid-sensing ion channel blocker on behavioral responses in a zebrafish model of acute visceral pain

Acid-sensing ion channels (ASICs) play significant roles in numerous neurological and pathological conditions, including pain. Although acid-induced nociception has been characterized previously in zebrafish, the contribution of ASICs in modulating pain-like behaviors is still unknown. Here, we investigated the role of amiloride, a nonselective ASICs blocker, in the negative modulation of specific behavioral responses in a zebrafish-based model of acute visceral pain. We verified that intraperitoneal injection (i.p.) of 0.25, 0.5, 1.0, and 2.0 mg/mL amiloride alone or vehicle did not change zebrafish behavior compared to saline-treated fish. Administration of 2.5% acetic acid (i.p.) elicited writhing-like response evidenced by the abnormal body curvature and impaired locomotion and motor activity. Attenuation of acetic acid-induced pain was verified at lower amiloride doses (0.25 and 0.5 mg/mL) whereas 1.0 and 2.0 mg/mL abolished pain-like responses. The protective effect of the highest amiloride dose tested was evident in preventing writhing-like responses and impaired locomotion and vertical activity. Collectively, amiloride antagonized abdominal writhing-like phenotype and aberrant behaviors, supporting the involvement of ASICs in a zebrafish-based model of acute visceral pain.