key: cord-0880740-h7wi8clh
authors: Hale, Martin; Garofoli, Mark; Raffa, Robert B
title: Benefit-Risk Analysis of Buprenorphine for Pain Management
date: 2021-05-24
journal: J Pain Res
DOI: 10.2147/jpr.s305146
sha: f8534aac27399eae7a993b410d07ea9c1e68bca2
doc_id: 880740
cord_uid: h7wi8clh

Health care providers in the United States are facing challenges in selecting appropriate medication for patients with acute and chronic pain in the midst of the current opioid crisis and COVID-19 pandemic. When compared with conventional opioids, the partial µ-opioid receptor agonist buprenorphine has unique pharmacologic properties that may be more desirable for pain management. The formulations of buprenorphine approved by the US Food and Drug Administration for pain management include intravenous injection, transdermal patch, and buccal film. A comparison of efficacy and safety data from studies of buprenorphine and conventional opioids suggests that buprenorphine may be a better-tolerated treatment option for many patients that provides similar or superior analgesia. Our benefit-risk assessment in this narrative review suggests that health care providers should consider that buprenorphine may be an appropriate alternative for pain management over other opioids.

As a result of the current opioid crisis, the United States is having difficulty providing adequate care for patients with acute and chronic pain. 1 Statistics from 2016 indicate that acute pain is reported by approximately 55% of hospitalized patients, and 50 million (20.4%) adults in the United States have chronic daily pain, with 19.6 million (8%) experiencing high-impact chronic pain that interferes with daily life or work activities. 2 Immediate-release/short-acting or extended-release (ER)/long-acting opioids are often prescribed for pain, as they elicit analgesia by acting on opioid receptors to inhibit nociceptive stimulation. 3 Increased prescribing rates coupled with the diversion of prescription opioids have contributed to the national crisis of opioid use disorder (addiction) and overdose deaths, signifying the need for safer alternatives. 4 Although abusedeterrent opioid formulations were designed to deter altered routes of administration (eg, snorting, inhalation, chewing, injection) that increase the risk of overdose, these formulations are not abuse-proof. 5 With advancing better practices in response to the opioid crisis, 17 of the 38 states with prescription opioid overdose death data saw a decline between 2017 and 2018, and no states experienced a significant increase. 4 However, opioid abuse rates have increased with the COVID-19 pandemic. 6 Opioids can be divided into conventional opioids (full µ-opioid receptor agonists such as fentanyl, hydrocodone, morphine, oxycodone) 7 and mixed-action or atypical opioids (such as buprenorphine, butorphanol, tramadol, tapentadol). 3 When compared with other opioids currently on the market, the atypical opioid buprenorphine has a unique pharmacologic profile. 8 Buprenorphine is a partial agonist with very high binding affinity at µ-opioid receptors, an agonist with low binding affinity at the nociceptin opioid receptor (NOP, formerly known as opioid receptor like-1), and an antagonist with high binding affinity at κ-and δopioid receptors (Figure 1 ). 9 The term "partial agonist" was applied owing to a partial effect on stimulating the receptor with in vitro assays. 10 This does not necessarily translate to partial analgesic efficacy in vivo or in clinical practice, as the analgesic signaling pathway may be sufficiently activated by a partial agonist. Partial agonism at the µ-opioid receptor by buprenorphine yields potent analgesia and a ceiling effect on respiratory depression and euphoria and reduces other adverse events commonly observed with conventional opioid use. 10−16 Buprenorphine does not occupy all µ-opioid receptors, which allows for efficacy of concomitant full µ-opioid receptor agonists. 9 Antagonism at the δ-and κ-opioid receptors may limit constipation, respiratory depression, dysphoria, and substance abuse. 9 Kappa-opioid receptor antagonists are currently being considered as promising therapeutics for psychiatric conditions such as depression, anxiety, and substance abuse disorders. 17 Agonism at NOP contributes to spinal analgesia and may limit the potential for substance abuse and tolerance commonly observed with full µ-opioid receptor agonists.

Conventional opioids bind to µ-opioid receptors, which activate signaling pathways that depress neural functions and are associated with adverse events. However, the partial agonistic effects of buprenorphine limit µ-opioid receptor activity, which elicits analgesia pathways but may restrict pathways associated with adverse events, contributing to a more favorable safety profile and patient satisfaction.

Buprenorphine is approved by the US Food and Drug Administration (FDA) for acute pain, chronic pain, opioid use disorder, or opioid dependence, depending on the formulation (Table 1) . 7, 18 Buprenorphine formulations exist as either a combination therapy with naloxone (eg, Suboxone and similar products) or as stand-alone products. The stand-alone buprenorphine products and their indications are listed in Table 1 . [19] [20] [21] [22] [23] [24] [25] [26] Buprenorphine also exists as a suppository, but this formulation is not FDAapproved for use in the US. 27 The purpose of this review is to present the literature assessing the efficacy of buprenorphine products for the treatment of pain and compare the risks and benefits of buprenorphine to conventional opioids. The information presented here can be used to aid health care professionals in medication selection for patients who are experiencing pain and for whom opioid treatment is deemed appropriate.

This narrative review is based on the authors' knowledge of the literature, their clinical experience, and literature searches including the terms buprenorphine and pain.

Although IV buprenorphine has not been studied in chronic pain, this formulation has been shown to have a dose-dependent analgesic effect in patients with acute pain. 28 IV buprenorphine had equal or superior analgesic efficacy to IV morphine for postoperative pain following abdominal, cardiac, lung, and spinal surgery or lateral thoracotomy. [29] [30] [31] [32] [33] [34] [35] [36] Bradley et al. found that 4 to 6 µg/kg IV buprenorphine following abdominal surgery (hysterectomy or cholecystectomy) provided more potent analgesia for a longer duration than morphine. 29 In a separate study, administration of intrathecal morphine and IV buprenorphine together alleviated pain and minimized sedation more effectively than either drug separately, with IV buprenorphine reducing the number of side effects when compared with morphine. 37 IV buprenorphine was also more effective than procaine for pain relief in patients with acute pancreatitis. 38 In addition to providing effective pain relief, a low-dose infusion (25 µg/h for 24 hours) of buprenorphine prevented the short-term development of secondary hyperalgesia around postoperative surgical incisions. 33

Although SL buprenorphine is not indicated for chronic pain, a systematic review of 10 chronic pain trials (6 studies used ≤400 µg/dose; 4 studies used ≥400 µg/dose; the dose range across all studies was 0.1-32 mg), including for the treatment of general, osteoarthritic, sickle-cell disease, nociceptive, and cancer chronic pain in the general, elderly, or pediatric populations, found this formulation to be efficacious in 100% of the studies. 39 For example, Malinoff et al. examined patients with chronic pain syndrome and found that pain decreased in 86% of patients following SL buprenorphine administration, and many patients reported improved mood, decreased sleep disturbance, and an improved sense of well-being after treatment. 40 For acute pain, SL buprenorphine had similar or greater postoperative analgesic efficacy when compared with IV patient-controlled analgesia (morphine) or intramuscular morphine following surgery ( Figure 2 ); however, significant relief was not observed until after 2 hours postdose, suggesting that IV buprenorphine may be more appropriate for immediate relief from severe acute pain. 41,42 SL buprenorphine (0.4 mg) also produced 

In a systematic review, transdermal buprenorphine was found to be efficacious in 29 (100%) clinical studies that examined chronic pain (general, low back, osteoarthritis, malignant, and musculoskeletal pain). 7 The dosages of transdermal buprenorphine used in these chronic pain studies ranged from 5 to 140 µg/h (the highest available dosage strength in the United States is 20 µg/h). Steiner et al. found that 12 weeks of treatment with transdermal buprenorphine resulted in significantly lower pain scores than placebo in opioid-naive patients with chronic low back pain. 44 A multicenter randomized phase 4 trial by Corli et al. showed that transdermal buprenorphine had analgesic efficacy similar to that of transdermal fentanyl, oral morphine, and oral oxycodone in patients with cancer pain (Figure 3) . 45 In addition, transdermal buprenorphine has demonstrated efficacy in the treatment of postsurgical acute pain to a similar or greater extent than oral tramadol or tramadol/acetaminophen. [46] [47] [48] Buccal Film Formulation

Buprenorphine buccal film (75 μg to 900 μg) has demonstrated analgesic efficacy in all currently published studies examining its effect on chronic low back pain ( Figure  4 ). [49] [50] [51] A retrospective analysis found that converting from a long-acting full µ-opioid receptor agonist to buprenorphine buccal film provided continued analgesia in most patients despite a reduction in daily morphine milligram equivalent (MME) factor, which could lead to improved patient safety outcomes. 52 To date, no studies have examined the effects of buprenorphine buccal film for acute pain, presenting a valuable opportunity for future research.

Among the formulations FDA-approved for chronic pain, buprenorphine buccal film has a higher bioavailability. Although buprenorphine has poor oral bioavailability and transdermal bioavailability is limited, the mucosa allows for higher bioavailability via the buccal route. 9 Buprenorphine buccal film also has a larger available dose range compared to the transdermal patch, which may be preferable for some patients ( Table 1 ). The 20 µg/h patch may not provide adequate analgesia in patients receiving high-dose opioid treatment (>80 mg MME factor/d). 20 The dose range of buprenorphine buccal film (75-900 µg) provides more flexibility to titrate to an optimal dose, making it a preferable option for patients whose needs exceed the doses available with the transdermal system. The highest dosage of transdermal buprenorphine available in the US is 20 μg/h (to be worn for 7 days), with the median equivalent dose of the buccal formulation being 300 μg/12 h. 53 Transdermal buprenorphine has the advantage of medication adherence with the ease of applying the product once a week, but it may also cause application site pruritus, erythema, and site rash, 44 which are treatment-emergent adverse events not reported in clinical studies of buprenorphine buccal film. [49] [50] [51] In clinical studies, 14% of patients with chronic pain discontinued transdermal buprenorphine owing to lack of perceived efficacy compared with 5% who discontinued buprenorphine buccal film for the same reason. 7 In similar clinical trials, responder analysis of ≥30% or ≥50% reduction in pain intensity in opioid-experienced patients showed that the efficacy of buprenorphine buccal film was greater than transdermal buprenorphine ( Figure 5 ). 7 The buccal film also has the advantage of additional safety data, where comparison with a conventional opioid (immediate-release oxycodone) in a clinical study assessing respiratory drive showed that, unlike oxycodone, buprenorphine buccal film had no significant impact on respiration. 54

Buprenorphine has a long-standing history of efficacy in postsurgical acute pain (IV formulation) and chronic pain (SL and transdermal formulations), and its clinical efficacy has been shown to be greater than that of morphine in some studies. 29, 39, 44 Buprenorphine has been suggested to be 25 to 115 times more potent as an analgesic than morphine (depending on the study), with no ceiling effect on analgesia. 9 Buprenorphine products no longer have an MME factor in the Centers for Disease Control opioid conversion guide, as they are not expected to be associated with overdose risk in the same dose-dependent manner as full µ-opioid receptor agonists. 55 In addition to morphine, the analgesic efficacy of buprenorphine has also been demonstrated to be equal to or greater than oxycodone (MME factor [mg]: 1.5) or fentanyl (MME factor for patch [µg]: 7.2) in chronic pain studies. 45, [55] [56] [57] [58] When compared across clinical studies, the efficacy of buprenorphine buccal film was similar to that of the conventional ER opioids hydromorphone, hydrocodone, and oxymorphone. 49, 51, [59] [60] [61] In a meta-analysis examining the effects of buprenorphine (SL, transdermal, and buccal) on chronic pain outcomes in patients with or without opioid use disorder (OUD), the authors found that efficacy was more pronounced in patients without OUD, and high doses may be needed for patients with OUD. 62 Overall, the data from these studies suggest that buprenorphine has equivalent or greater clinical analgesic efficacy than conventional opioids.

Buprenorphine is a Schedule III drug with a unique mechanism of action that has less potential for abuse than Schedule II drugs (eg, morphine, oxycodone, fentanyl). 63 The lower abuse potential of buprenorphine may mitigate the number of overdose deaths observed with conventional opioids. 64 Opioids are commonly used recreationally and carry a high risk of diversion; therefore, choosing an opioid medication with slower absorption and less drug liking and abuse potential is imperative during the current opioid crisis. The risks of drug dependence and analgesic tolerance are also lower for buprenorphine than for conventional opioids. 15, 65, 66 Buprenorphine also reduces the potential for respiratory depression and death compared with conventional opioids. 1, 10, 11 No cases of respiratory depression were reported in any clinical trials of buprenorphine buccal film. [49] [50] [51] In a phase 1 study, buprenorphine buccal film 300, 600, or 900 µg did not negatively impact respiratory drive, whereas oxycodone 30 mg and 60 mg significantly reduced respiratory drive (Figure 6 ). 54 The clinical trials of buprenorphine buccal film included fewer than 1000 67 This is approximately 80 times less than what was observed in a separate study of transdermal fentanyl. 68 While IV buprenorphine may cause some respiratory depression, studies have demonstrated that it plateaus with a ceiling effect, whereas conventional opioids such as fentanyl do not. 11, 12 Sedatives such as benzodiazepines and alcohol increase the risk of respiratory depression, and benzodiazepines are not recommended to be prescribed in combination with any opioids. 1 Because the risk of respiratory depression appears to be lower with buprenorphine than with conventional opioids, an overdose may be less likely to result in a fatality.

In addition to a decreased risk of respiratory depression, other tolerability factors like constipation are more favorable with buprenorphine. Constipation rates for ER full μ-opioid receptor agonists range from 8% to 23%, [69] [70] [71] [72] while constipation was reported in only 4% of patients receiving buprenorphine buccal film and in 13% of patients receiving transdermal buprenorphine. 20, 21 In a postmarketing surveillance study, 128 (1%) of 13,179 patients receiving transdermal buprenorphine experienced constipation. 67 Opioid-induced constipation is associated with increased economic burden and reduced quality of life, so buprenorphine may be preferable to conventional opioids when considering this adverse event. 73 In addition, a comparison of adverse events reported in clinical trials for buprenorphine buccal film and ER formulations of oxycodone, hydromorphone, and oxymorphone showed that the proportion of patients who experienced nausea, vomiting, constipation, headache, dizziness, somnolence, anxiety, and dry mouth was lower with buprenorphine buccal film than with conventional opioids (Figure 7) .

Unlike with conventional opioids, additional benefits of buprenorphine due to its unique metabolism include suitability for use in patients requiring concomitant medications, those with renal or hepatic impairment, and the elderly. 14 Most patients with OUD have been found to also have chronic pain, and among them, the majority had chronic pain before their first OUD diagnosis, making appropriate treatment in this subset of patients essential. 74 Patients with comorbid chronic pain and OUD have reported satisfaction with buprenorphine treatment. 75 Also, buprenorphine is not immunosuppressive, 76, 77 does not negatively impact the DovePress hypothalamic-pituitary-adrenal pathway, [78] [79] [80] and may reduce anxiety and depression. [81] [82] [83] [84] Overall, the safety data and additional benefits of buprenorphine suggest that it has a lower risk of adverse events compared with conventional opioids, most notably with respiratory depression. However, all opioids, including buprenorphine, carry the risk of adverse events and addiction potential, depending on the dose. Therefore, careful consideration should be given to the risks and benefits of each opioid before prescribing. Health care providers should consider using one or more opioid risk screening tools before the initiation of any opioid therapy. 85, 86 Conclusions Clinical safety and efficacy data in this narrative review suggest that buprenorphine may be a more tolerable alternative with equivalent or superior analgesia to conventional opioids for patients with pain. IV buprenorphine has been the most extensively studied formulation and is FDA-approved for acute pain, while the transdermal patch and buccal film are FDA-approved for chronic pain. The transdermal patch has demonstrated efficacy for chronic pain with once-weekly dosing. Health care providers may find that the buprenorphine buccal film formulation has favorable bioavailability, available doses, efficacy, adverse event profile, and benefit-risk assessments for the treatment of chronic pain. Clinicians should always consider the benefits and risks of various therapeutic options for pain management and are encouraged to explore their unique aspects, long-term clinical impact, and individual patient needs. 

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Professional writing and editorial support was provided by MedLogix Communications, LLC, Itasca, Illinois, under the direction of the authors and was funded by BioDelivery Sciences International, Inc. No author received financial compensation for writing or directing the content of this manuscript.

All authors contributed to the conception and design of the manuscript, analysis and interpretation of data, and critical evaluation of the manuscript for scientific accuracy and intellectual content; approved the final manuscript for publication; and agreed to be accountable for all aspects of the work.

MH has served on advisory boards for BioDelivery Sciences International, Inc. and was principal investigator for multiple buprenorphine trials. MG has served on advisory boards for Daiichi Sankyo, Inc. RBR is the CSO of Neumentum Inc.; cofounder of CaRafe Drug Innovation, LLC; and cofounder of Enalare Therapeutics Inc. The authors report no other conflicts of interest in this work.