Buprenorphine: an analgesic with an expanding role in the treatment of opioid addiction

Systematic Structure-Activity Relationship Study of Nalfurafine Analogues toward Development of Potentially Nonaddictive Pain Management Treatments

Despite the availability of numerous pain medications, the current array of Food and Drug Administration-approved options falls short in adequately addressing pain states for numerous patients and consequently worsens the opioid crisis. Thus, it is imperative for basic research to develop novel and nonaddictive pain medications. Toward addressing this clinical goal, nalfurafine (NLF) was chosen as a lead and its structure-activity relationship (SAR) systematically studied through design, syntheses, and in vivo characterization of 24 analogues. Two analogues, 21 and 23, showed longer durations of action than NLF in a warm-water tail immersion assay, produced in vivo effects primarily mediated by KOR and DOR, penetrated the blood-brain barrier, and did not function as reinforcers. Additionally, 21 produced fewer sedative effects than NLF. Taken together, these results aid the understanding of NLF SAR and provide insights for future endeavors in developing novel nonaddictive therapeutics to treat pain.

Dysphagia as a Missing Link Between Post-surgical- and Opioid-Related Pneumonia

PURPOSE

Postoperative pneumonia remains a common complication of surgery, despite increased attention. The purpose of our study was to determine the effects of routine surgery and post-surgical opioid administration on airway protection risk.

METHODS

Eight healthy adult cats were evaluated to determine changes in airway protection status and for evidence of dysphagia in two experiments. (1) In four female cats, airway protection status was tracked following routine abdominal surgery (spay surgery) plus low-dose opioid administration (buprenorphine 0.015 mg/kg, IM, q8-12 h; n = 5). (2) Using a cross-over design, four naive cats (2 male, 2 female) were treated with moderate-dose (0.02 mg/kg) or high-dose (0.04 mg/kg) buprenorphine (IM, q8-12 h; n = 5).

RESULTS

Airway protection was significantly affected in both experiments, but the most severe deficits occurred post-surgically as 75% of the animals exhibited silent aspiration.

CONCLUSION

Oropharyngeal swallow is impaired by the partial mu-opioid receptor agonist buprenorphine, most remarkably in the postoperative setting. These findings have implications for the prevention and management of aspiration pneumonia in vulnerable populations.

Serotonin therapies for opioid-induced disordered swallow and respiratory depression

Opioids are well-known to cause respiratory depression, but despite clinical evidence of dysphagia, the effects of opioids on swallow excitability and motor pattern are unknown. We tested the effects of the clinically relevant opioid buprenorphine on pharyngeal swallow and respiratory drive in male and female rats. We also evaluated the utility of 5-HT1A agonists (8-OH-DPAT and buspirone) to improve swallowing and breathing following buprenorphine administration. Experiments were performed on 44 freely breathing Sprague-Dawley rats anesthetized with sodium pentobarbital. Bipolar fine wire electrodes were inserted into the mylohyoid, thyroarytenoid, posterior cricoarytenoid, thyropharyngeus, and diaphragm muscles to measure electromyographic (EMG) activity of swallowing and breathing. We evaluated the hypotheses that swallowing varies by stimulus, opioids depress swallowing and breathing, and that 5-HT1A agonists improve these depressions. Our results largely confirmed the following hypotheses: 1) swallow-related EMG activity was larger during swallows elicited by esophageal distension plus oral water infusion than by either stimulus alone. 2) Buprenorphine depressed swallow in both sexes, but females were more susceptible to total swallow suppression. 3) Female animals were also more vulnerable to opioid-induced respiratory depression. 4) 8-OH-DPAT rescued breathing following buprenorphine-induced respiratory arrest, and pretreatment with the partial 5-HT1A agonist buspirone prevented buprenorphine-induced respiratory arrest in female animals. 5) 8-OH-DPAT enhanced mylohyoid and thyropharyngeus EMG amplitude during swallow but did not restore excitability of the swallow pattern generator following total suppression by buprenorphine. Our results highlight sex-specific and behavior-specific effects of buprenorphine and provide preclinical evidence of a 5HT1A agonist for the treatment of respiratory depression and dysphagia.NEW & NOTEWORTHY This is the first study, to our knowledge, to evaluate sex-specific effects of opioid administration on pharyngeal swallow. We expand on a small but growing number of studies that report a lower threshold for opioid-induced respiratory depression in females compared with males, and we are the first to produce this effect with the partial μ-opioid-receptor agonist buprenorphine. This is the first demonstration, to our knowledge, that activation of 5-HT1A receptors can improve swallow and breathing outcomes following systemic buprenorphine administration.

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.

Harmful effects of opioid use in pregnancy: A scientific review commissioned by the European Board and College of obstetrics and gynaecology (EBCOG)

Caring for pregnant women who have a recreational opioid use disorder is a common clinical challenge in modern obstetric care. These are an elusive population who often have multiple social issues that complicate their pregnancy management. Comprehensive and supportive maternal care can motivate these mothers to change her lifestyle. Multidisciplinary non-judgemental approach with appropriate medication and management, can result in good pregnancy outcomes for mother and her baby.

Changes in Psychological Outcomes after Cessation of Full Mu Agonist Long-Term Opioid Therapy for Chronic Pain

Improved understanding of psychological features associated with full mu agonist long-term opioid therapy (LTOT) cessation may offer advantages for clinicians. This preliminary study presents changes in psychological outcomes in patients with chronic, non-cancer pain (CNCP) after LTOT cessation via a 10-week multidisciplinary program which included treatment with buprenorphine. Paired t-tests pre- and post-LTOT cessation were compared in this retrospective cohort review of data from electronic medical records of 98 patients who successfully ceased LTOT between the dates of October 2017 to December 2019. Indicators of quality of life, depression, catastrophizing, and fear avoidance, as measured by the 36-Item Short Form Survey, the Patient Health Questionnaire-9-Item Scale, the Pain Catastrophizing Scale, and the Fear Avoidance Belief Questionnaires revealed significant improvement. Scores did not significantly improve for daytime sleepiness, generalized anxiety, and kinesiophobia, as measured by the Epworth Sleepiness Scale, the Generalized Anxiety Disorder 7-Item Scale, and the Tampa Scale of Kinesiophobia. The results suggest that successful LTOT cessation may be interconnected with improvements in specific psychological states.

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.

Prenatal exposure to opioids: Associations between the caregiving environment and externalizing behaviors

Maternal opioid use during pregnancy is a rapidly growing public health crisis and is associated with a range of adverse developmental outcomes including externalizing behaviors among exposed children. Recent work has highlighted the role of indirect pathways from prenatal opioid exposure to behavioral outcomes through aspects of the caregiving environment, including parenting. This review highlights maternal sensitivity and related aspects of the caregiving environment that may impact the development of externalizing behaviors among children with a history of prenatal exposure to opioids. We conclude by providing suggestions for future directions in research examining development among children with prenatal opioid exposure.

Mechanisms Underlying the Anti-Suicidal Treatment Potential of Buprenorphine

Death by suicide is a global epidemic with over 800 K suicidal deaths worlwide in 2012. Suicide is the 10th leading cause of death among Americans and more than 44 K people died by suicide in 2019 in the United States. Patients with chronic pain, including, but not limited to, those with substance use disorders, are particularly vulnerable. Chronic pain patients have twice the risk of death by suicide compared to those without pain, and 50% of chronic pain patients report that they have considered suicide at some point due to their pain. The kappa opioid system is implicated in negative mood states including dysphoria, depression, and anxiety, and recent evidence shows that chronic pain increases the function of this system in limbic brain regions important for affect and motivation. Additionally, dynorphin, the endogenous ligand that activates the kappa opioid receptor is increased in the caudate putamen of human suicide victims. A potential treatment for reducing suicidal ideation and suicidal attempts is buprenorphine. Buprenorphine, a partial mu opioid agonist with kappa opioid antagonist properties, reduced suicidal ideation in chronic pain patients with and without an opioid use disorder. This review will highlight the clinical and preclinical evidence to support the use of buprenorphine in mitigating pain-induced negative affective states and suicidal thoughts, where these effects are at least partially mediated via its kappa antagonist properties.

Benefit-Risk Analysis of Buprenorphine for Pain Management

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.

Is Buprenorphine Effective for Chronic Pain? A Systematic Review and Meta-analysis

OBJECTIVE

The objective was to perform a systematic review and meta-analysis of the literature on the effects of buprenorphine on chronic pain outcomes (i.e., patient-reported pain intensity) in patients with and without opioid use disorder (OUD).

DESIGN

Ovid/Medline, PubMed, Embase, and the Cochrane Library were searched for studies that explored the effectiveness (in reducing pain) of buprenorphine treatment for chronic pain patients with and without a history of OUD. Randomized controlled trials and observational studies were included in the review.

METHODS

Two separate searches were conducted to identify buprenorphine trials that included chronic pain patients either with or without OUD. Five studies used validated pain report measures and included a chronic pain population with OUD. Nine studies used validated report measures and included chronic pain patients without OUD. Meta-analysis was performed using the R, version 3.2.2, Metafor package, version 1.9-7.

RESULTS

The meta-analysis revealed that buprenorphine has a beneficial effect on pain intensity overall, with a small mean effect size in patients with comorbid chronic pain and OUD and a moderate- to large-sized effect in chronic pain patients without OUD.

CONCLUSIONS

Our results indicate that buprenorphine is modestly beneficial in reducing pain intensity in patients without OUD. Although informative, these findings should be carefully interpreted due to the small amount of data available and the variation in study designs.

A review of the existing literature on buprenorphine pharmacogenomics

Buprenorphine is an effective treatment for opioid dependence; however, it demonstrates individual variability in efficacy. Pharmacogenomics may explain this drug response variability and could allow for tailored therapy on an individual basis. The Food and Drug Administration and the Clinical Pharmacogenomics Implementation Consortium have guidelines on pharmacogenomic testing for some opioids (e.g., codeine); however, no guidelines exist for the partial opioid agonist buprenorphine. Pharmacogenomic testing targets for buprenorphine include pharmacodynamic genes like the mu-opioid receptor (MOP receptor) and catechol-O-methyltransferase (COMT), as well as the pharmacokinetic genes like the CYP enzymes. In this review we identified genotypes in patients with opioid addiction receiving buprenorphine that may result in altered therapeutic dosing and increased rate of relapse. The OPRM1 A118G single nucleotide polymorphism (SNP rs1799971) gene variant encoding the N40D MOP receptor has been associated with variable efficacy and response to treatment in both adult and neonatal patients receiving buprenorphine for treatment of opioid withdrawal. An SNP associated with rs678849 of OPRD1, coding for the delta opioid receptor, was associated with opioid relapse as indicated by opioid positive urine drug screens; there was also sex specific SNP identified at rs581111 and rs529520 in the European American population. COMT variability, particularly in rs4680, has been associated with length of stay and need for opioid treatment in patients with neonatal abstinence syndrome. Variations of the pharmacokinetic gene for CYP3A4 showed that the ultrarapid metabolizer phenotype required higher doses of buprenorphine. Genotyping of patients may allow us to appropriately tailor buprenorphine therapy to individual patients and lead to improved patient outcomes; however, further research on the pharmacogenomics of buprenorphine is needed.

Prenatal exposure to methadone or buprenorphine alters µ-opioid receptor binding and downstream signaling in the rat brain

There is a growing concern related to the use of opioid maintenance treatment during pregnancy. Studies in both humans and animals have reported reduced cognitive functioning in offspring prenatally exposed to methadone or buprenorphine; however, little is known about the neurobiological mechanisms underlying these impairments. To reveal possible neurobiological effects of such in utero exposure, we examined brain tissue from methadone- and buprenorphine-exposed rat offspring previously shown to display impaired learning and memory. We studied µ-opioid receptor (MOR) and N-methyl-D-aspartate receptor (NMDAR) binding in the rat offspring cerebrum during development and in the hippocampus at young adulthood. Moreover, we examined activation of the Ca2+ /calmodulin-dependent protein kinase II (CaMKII) and the extracellular signal-regulated kinase (ERK), which are central in the downstream signaling of these receptors. The methadone- and buprenorphine-exposed rat pups displayed reduced MOR binding up to two weeks after birth, whereas the NMDAR binding was unaffected. Prenatal exposure to methadone or buprenorphine also resulted in decreased activation of CaMKII and/or ERK during development, while young adult offspring displayed increased hippocampal ERK activation. In conclusion, our findings suggest that prenatal exposure to exogenous opioids, such as methadone or buprenorphine, may disturb the endogenous opioid system during development, with long-term effects on proteins important for cognitive functioning.

The Therapeutic Potential of Novel Kappa Opioid Receptor-based Treatments

INTRODUCTION

Similarly to the μ opioid receptor, kappa opioid receptor (KOR), is present either in the central nervous system or in peripheral tissues. In the last years, several molecules, able to interact with KOR, have been the focus of basic research for their therapeutic potential in the field of chronic pain, as well as in depression, autoimmune disorders and neurological diseases.

DISCUSSION

The role of KOR system and the consequent clinical effects derived by its activation or inhibition are discussed. Their potential therapeutic utilization in conditions of stress and drug relapse, besides chronic pain, is presented here, including the possible use of KORagonists in drug addiction. Moreover, the potential role of KOR-antagonists, KOR agonistantagonists and peripheral KOR agonists is proposed.

CONCLUSION

Other than pain, KORs have a role in regulating reward and mood. Due to its location, KORs seem to mediate interactions between psychiatric disorders, addiction and depression. Experimental studies in animal models have identified brain mechanisms that may contribute to clarify specific pathophysiological processes.

Buprenorphine buccal film for chronic pain management

Buprenorphine is a Schedule III opioid with unique pharmacodynamic and pharmacokinetic properties that contribute to effective analgesia and fewer safety risks than other opioids. This review article focuses on the buccal film formulation, which is preferable to other buprenorphine formulations on the basis of bioavailability, safety and efficacy. The clinical studies reviewed here confirm that buprenorphine buccal film offers effective and continuous pain relief that is generally well tolerated, with no cases of respiratory depression reported in any of the studies. On the basis of these clinical data and individual patient risk/benefit assessments, clinicians should consider utilizing buprenorphine buccal film as a first-line opioid treatment for chronic pain over other buprenorphine formulations or other opioids.

A Narrative Pharmacological Review of Buprenorphine: A Unique Opioid for the Treatment of Chronic Pain

Buprenorphine is a Schedule III opioid analgesic with unique pharmacodynamic and pharmacokinetic properties that may be preferable to those of Schedule II full μ-opioid receptor agonists. The structure of buprenorphine allows for multimechanistic interactions with opioid receptors μ, δ, κ, and opioid receptor-like 1. Buprenorphine is considered a partial agonist with very high binding affinity for the μ-opioid receptor, an antagonist with high binding affinity for the δ- and κ-opioid receptors, and an agonist with low binding affinity for the opioid receptor-like 1 receptor. Partial agonism at the μ-opioid receptor does not provide partial analgesia, but rather analgesia equivalent to that of full μ-opioid receptor agonists. In addition, unlike full μ-opioid receptor agonists, buprenorphine may have a unique role in mediating analgesic signaling at spinal opioid receptors while having less of an effect on brain receptors, potentially limiting classic opioid-related adverse events such as euphoria, addiction, or respiratory depression. The pharmacokinetic properties of buprenorphine are also advantageous in a clinical setting, where metabolic and excretory pathways allow for use in patients requiring concomitant medications, the elderly, and those with renal or hepatic impairment. The unique pharmacodynamic and pharmacokinetic properties of buprenorphine translate to an effective analgesic with a potentially favorable safety profile compared with that of full μ-opioid receptor agonists for the treatment of chronic pain.

Safety And Efficacy Of The Unique Opioid Buprenorphine For The Treatment Of Chronic Pain

BACKGROUND

Chronic pain is associated with decreased quality of life and is one of the most common reasons adults seek medical care, making treatment imperative for many aspects of patient well-being. Chronic pain management typically involves the use of Schedule II full μ-opioid receptor agonists for pain relief; however, the increasing prevalence of opioid addiction is a national crisis that is impacting public health and social and economic welfare. Buprenorphine is a Schedule III partial μ-opioid receptor agonist that is an equally effective but potentially safer treatment option for chronic pain than full μ-opioid receptor agonists. The purpose of this review is to provide an overview of the clinical efficacy and safety of the transdermal and buccal formulations of buprenorphine, which are approved by the Food and Drug Administration for chronic pain, compared with that of extended-release full μ-opioid receptor agonists.

METHODS

Controlled or randomized controlled clinical trial information was retrieved from EMBASE, Medline, and PubMed using the search terms "buprenorphine" AND "chronic" AND "pain."

RESULTS

A total of 33 clinical studies were ultimately used in this review, including 29 (88%) on transdermal buprenorphine and 4 (12%) on buprenorphine buccal film. Although the measure of pain intensity varied among studies, each of these 33 trials demonstrated efficacy for buprenorphine in pain relief. A total of 28 studies also assessed safety, with each concluding that buprenorphine was generally well tolerated.

CONCLUSION

Comparison of current clinical data along with results of responder and safety analyses support the use of buprenorphine over full μ-opioid receptor agonists for effective preferential treatment of chronic pain; however, head-to-head clinical studies are warranted.

Craving in Opioid Use Disorder: From Neurobiology to Clinical Practice

Opioid use disorder (OUD) is a major public health issue that has reached epidemic levels in some parts of the world. It is a chronic and complex neurobiological disease associated with frequent relapse to drug taking. Craving, defined as an overwhelmingly strong desire or need to use a drug, is a central component of OUD and other substance use disorders. In this review, we describe the neurobiological and neuroendocrine pathways that underpin craving in OUD and also focus on the importance of assessing and treating craving in clinical practice. Craving is strongly associated with patients returning to opioid misuse and is therefore an important treatment target to reduce the risk of relapse and improve patients' quality of life. Opioid agonist therapies (OAT), such as buprenorphine and methadone, can significantly reduce craving and relapse risk, and it is essential that patients are treated optimally with these therapies. There is also evidence to support the benefits of non-pharmacological approaches, such as cognitive behavioral therapy and mindfulness-based interventions, as supplementary treatments to opioid agonist therapies. However, despite the positive impact of these treatments on craving, many OUD patients continue to suffer with negative affect and dysphoria. There is a clear need for further studies to progress our understanding of the neurobiological basis of craving and addiction and to identify novel therapeutic strategies as well as to optimize the use of existing treatments to improve outcomes for the growing numbers of patients affected by OUD.

Butorphanol-Azaperone-Medetomidine for the Immobilization of Rhesus Macaques (Macaca mulatta)

Maximizing animal wellbeing by minimizing drug-related side effects is a key consideration when choosing pharmaceutical agents for chemical restraint in nonhuman primates. One drug combination that may promote this ideology is butorphanol (27.3 mg/mL), azaperone (9.1 mg/mL), and medetomidine (10.9 mg/mL; BAM). Based on results from a pilot study, 2 doses of BAM (16 and 24 μL/kg IM) were compared in healthy, 3-y-old rhesus macaques. Physiologic parameters and anesthetic quality were assessed and recorded every 5 min. Experimental endpoints were established for hypoxemia (85% or less peripheral oxygen saturation with oxygen supplementation), pulse rate (80 bpm or less for 2 consecutive readings), mean arterial pressure (MAP; 50 mm Hg or less), and hypothermia (97 °F or less); if any endpoint was achieved, medetomidine was reversed by using atipamezole (0.22 mg/kg IM). Both BAM doses resulted in immobilization of all animals with no clinically significant differences between groups. All animals initially exhibited hypoxemia that resolved with oxygen supplementation. Regardless of dose, most macaques (71%) reached established experimental endpoints for bradycardia (62 to 80 bpm) or hypotension (44 to 50 mm Hg MAP). Given the results of this study, our recommendation regarding the use of 16- or 24-μL/kg BAM for immobilizing rhesus macaques is dependent on caution regarding cardiopulmonary parameters and the provision of supplemental oxygen.

Early life opioid exposure and potential long-term effects

The long-term consequences of perinatal opioid exposure and subsequent development of neonatal opioid withdrawal syndrome is largely unknown and likely dependent on a multitude of factors, including co-morbid drug use, pre- and post-natal care, and individual factors including the maternal-infant relationship and home environment. This review summarizes the current literature from clinical and preclinical studies on perinatal opioid exposure, focusing on the consequences in the offspring. Although a large number of preclinical studies have been conducted examining the impact of prenatal opioid exposure, the models employed are not necessarily representative of clinical use patterns, making it challenging to translate these results to the impacted population. Use of more clinically-relevant models of perinatal opioid exposure are requisite for the development of improved pharmacological and behavioral treatment strategies to improve quality of life for this vulnerable population.

Pharmacologic Treatment of Opioid Use Disorder: a Review of Pharmacotherapy, Adjuncts, and Toxicity

Opioid use disorder continues to be a significant source of morbidity and mortality in the USA and the world. Pharmacologic treatment with methadone and buprenorphine has been shown to be effective at retaining people in treatment programs, decreasing illicit opioid use, decreasing rates of hepatitis B, and reducing all cause and overdose mortality. Unfortunately, barriers exist in accessing these lifesaving medications: users wishing to start buprenorphine therapy require a waivered provider to prescribe the medication, while some states have no methadone clinics. As such, users looking to wean themselves from opioids or treat their opioid dependence will turn to alternative agents. These agents include using prescription medications, like clonidine or gabapentin, off-label, or over the counter drugs, like loperamide, in supratherapeutic doses. This review provides information on the pharmacology and the toxic effects of pharmacologic agents that are used to treat opioid use disorder. The xenobiotics reviewed in depth include buprenorphine, clonidine, kratom, loperamide, and methadone, with additional information provided on lofexidine, akuamma seeds, kava, and gabapentin.

To Stop or Not, That Is the Question: Acute Pain Management for the Patient on Chronic Buprenorphine

Perioperative pain management suggestions for patients taking buprenorphine and presenting for elective and urgent/emergent surgery have been developed and are described here.

Advances in the delivery of buprenorphine for opioid dependence

Opioid use disorders (OUDs) have long been a global problem, but the prevalence rates have increased over 20 years to epidemic proportions in the US, with concomitant increases in morbidity and all-cause mortality, but especially opioid overdose. These increases are in part attributable to a several-fold expansion in the prescription of opioid pain medications over the same time period. Opioid detoxification and psychosocial treatments alone have each not yielded sufficient efficacy for OUD, but μ-opioid receptor agonist, partial agonist, and antagonist medications have demonstrated the greatest overall benefit in OUD treatment. Buprenorphine, a μ-opioid receptor partial agonist, has been used successfully on an international basis for several decades in sublingual tablet and film preparations for the treatment of OUD, but the nature of formulation, which is typically self-administered, renders it susceptible to nonadherence, diversion, and accidental exposure. This article reviews the clinical trial data for novel buprenorphine delivery systems in the form of subcutaneous depot injections, transdermal patches, and subdermal implants for the treatment of OUD and discusses both the clinical efficacy of longer-acting formulations through increasing consistent medication exposure and their potential utility in reducing diversion. These new delivery systems also offer new dosing opportunities for buprenorphine and strategies for dosing intervals in the treatment of OUD.

Participation of dorsal periaqueductal gray 5-HT1A receptors in the panicolytic-like effect of the κ-opioid receptor antagonist Nor-BNI

Panic patients may have abnormalities in serotonergic and opioidergic neurotransmission. The dorsal periaqueductal gray (dPAG) plays an important role in organizing proximal defense, related to panic attacks. The 5-HT_1A receptor (5-HT_1A-R) is involved in regulating escape behavior that is organized in the dPAG. Activation of κ-opioid receptor (KOR) in this region causes anxiogenic effects. In this study, we investigated the involvement of KOR in regulating escape behavior, using systemic and intra-dPAG injection of the KOR antagonist Nor-BNI. As panic models, we used the elevated T-maze (ETM) and the dPAG electrical stimulation test (EST). We also evaluated whether activation of the 5-HT_1A-R or the μ-opioid receptor (MOR) in the dPAG contributes to the Nor-BNI effects. The results showed that systemic administration of Nor-BNI, either subcutaneously (2.0 and 4.0mg/kg) or intraperitoneally (2.0mg/kg), impaired escape in the EST, indicating a panicolytic-like effect. Intra-dPAG injection of this antagonist (6.8nmol) caused the same effect in the EST and in the ETM. Association of ineffective doses of Nor-BNI and the 5-HT_1A-R agonist 8-OH-DPAT caused panicolytic-like effect in these two tests. Previous administration of the 5-HT_1A-R antagonist WAY-100635, but not of the MOR antagonist CTOP, blocked the panicolytic-like effect of Nor-BNI. These results indicate that KOR enhances proximal defense in the dPAG through 5-HT_1A-R modulation, independently of MOR. Because former results indicate that the 5-HT_1A-R is involved in the antipanic action of antidepressants, KOR antagonists may be useful as adjunctive or alternative drug treatment of panic disorder.

Efficacy and tolerability of buccal buprenorphine in opioid-naive patients with moderate to severe chronic low back pain

OBJECTIVES

Buprenorphine HCl buccal film has been developed for treating chronic pain utilizing BioErodible MucoAdhesive (BEMA(®)) delivery technology. Buccal buprenorphine (BBUP; Belbuca(TM), Endo Pharmaceuticals) was evaluated for the management of moderate to severe chronic low back pain (CLBP) requiring around-the-clock analgesia in a multicenter, double-blind, placebo-controlled, enriched-enrollment, randomized-withdrawal study in opioid-naive patients.

METHODS

Patients (n = 749) were titrated to a dose of BBUP (range, 150-450 µg every 12 h) that was generally well tolerated and provided adequate analgesia for ≥14 days, and then randomized to BBUP (n = 229) or placebo (n = 232), respectively. The primary efficacy variable was the change from baseline to week 12 of double-blind treatment in the mean of daily average pain intensity scores (numeric rating scale from 0 [no pain] to 10 [worst pain imaginable]).

RESULTS

Patients were experiencing moderate to severe pain at study entry: mean (SD) = 7.15 (1.05). Following titration, pain was reduced to the mild range; 2.81 (1.07). After randomization, mean (SD) pain scores increased from baseline to week 12 more with placebo (1.59 [2.04]) versus BBUP: (0.94 [1.85]) with a significant between-group difference (-0.67 [95% CI: -1.07 to -0.26]; p = 0.0012). A significantly larger percentage of patients receiving BBUP versus placebo had ≥30% pain reduction (63% vs 47%; p = 0.0012). During double-blind treatment, the most frequent adverse events (AEs) with BBUP were nausea (10%), constipation (4%) and vomiting (4%). The most common AEs with placebo were nausea (7%), upper respiratory tract infection (4%), headache (3%) and diarrhea (3%).

CONCLUSIONS

These findings demonstrate the efficacy and tolerability of BBUP among opioid-naive patients requiring around-the-clock opioid treatment for CLBP.

Interim buprenorphine treatment in opiate dependence: A pilot effectiveness study

BACKGROUND

Interim methadone treatment (i.e., temporary medication-only treatment) has been tested in a few U.S. studies as a method for facilitated referral to and initiation of opioid maintenance treatment in heroin dependence. However, despite the favorable safety profile of buprenorphine compared with methadone, interim treatment with buprenorphine rarely has been tested and reported in the scientific literature. The present pilot effectiveness study aims to assess the feasibility of an interim buprenorphine treatment for initiation of individuals with opiate dependence into full-scale opioid maintenance treatment, and to study baseline predictors of successful transfer to full-scale treatment.

METHODS

Interim treatment was introduced in a high-threshold setting with waiting lists to opioid maintenance treatment. Consecutive patients on the waiting list were offered the option to enter interim treatment. The interim program was a medication-only condition with supervised daily doses of buprenorphine-naloxone. The main outcome was successful transfer to full-scale opioid maintenance treatment, which required a drug-free urine sample.

RESULTS

Forty-four patients entered interim buprenorphine treatment. Among them, 57% (n = 25) were successfully transferred to full-scale treatment after an average of 44 days. Remaining patients could not be transferred, generally because they did not manage to become drug-free. Successful transfer to full-scale treatment was associated with a lower baseline Alcohol Use Disorders Identification Test (AUDIT) score (4.4 vs. 12.6; P < .001) and tended to be associated with lower cannabis use (5.2 vs. 10.4 days during the past 30 days; P = .06) and lower heroin use (7.2 vs. 9.9 days; P = .09) prior to baseline. In a logistic regression analysis, only lower AUDIT score predicted successful treatment entry.

CONCLUSIONS

According to these pilot data, supervised buprenorphine-naloxone in a medication-only interim treatment condition appears to be a feasible way to improve treatment initiation in a high-threshold setting. Polydrug use, including higher levels of alcohol consumption, may predict a more complicated course in interim treatment.

Helix-constrained nociceptin peptides are potent agonists and antagonists of ORL-1 and nociception

Nociceptin (orphanin FQ) is a 17-residue neuropeptide hormone with roles in both nociception and analgesia. It is an opioid-like peptide that binds to and activates the G-protein-coupled receptor opioid receptor-like-1 (ORL-1, NOP, orphanin FQ receptor, kappa-type 3 opioid receptor) on central and peripheral nervous tissue, without activating classic delta-, kappa-, or mu-opioid receptors or being inhibited by the classic opioid antagonist naloxone. The three-dimensional structure of ORL-1 was recently published, and the activation mechanism is believed to involve capture by ORL-1 of the high-affinity binding, prohelical C-terminus. This likely anchors the receptor-activating N-terminus of nociception nearby for insertion in the membrane-spanning helices of ORL-1. In search of higher agonist potency, two lysine and two aspartate residues were strategically incorporated into the receptor-binding C-terminus of the nociceptin sequence and two Lys(i)→Asp(i+4) side chain-side chain condensations were used to generate lactam cross-links that constrained nociceptin into a highly stable α-helix in water. A cell-based assay was developed using natively expressed ORL-1 receptors on mouse neuroblastoma cells to measure phosphorylated ERK as a reporter of agonist-induced receptor activation and intracellular signaling. Agonist activity was increased up to 20-fold over native nociceptin using a combination of this helix-inducing strategy and other amino acid modifications. An NMR-derived three-dimensional solution structure is described for a potent ORL-1 agonist derived from nociceptin, along with structure-activity relationships leading to the most potent known α-helical ORL-1 agonist (EC₅₀ 40 pM, pERK, Neuro-2a cells) and antagonist (IC₅₀ 7 nM, pERK, Neuro-2a cells). These α-helix-constrained mimetics of nociceptin(1-17) had enhanced serum stability relative to unconstrained peptide analogues and nociceptin itself, were not cytotoxic, and displayed potent thermal analgesic and antianalgesic properties in rats (ED₅₀ 70 pmol, IC₅₀ 10 nmol, s.c.), suggesting promising uses in vivo for the treatment of pain and other ORL-1-mediated responses.

Association between gene variants and response to buprenorphine maintenance treatment

A variety of studies were addressed to differentiate responders and non-responders to substitution treatment among heroin dependent patients, without conclusive findings. In particular, preliminary pharmacogenetic findings have been reported to predict treatment effectiveness in mental health and substance use disorders. Aim of the present study was to investigate the possible association of buprenorphine (BUP) treatment outcome with gene variants that may affect kappa-opioid receptors and dopamine system function. One hundred and seven heroin addicts (West European, Caucasians) who underwent buprenorphine maintenance treatment were genotyped and classified into two groups (A and B) on the basis of treatment outcome. Non-responders to buprenorphine (group B) have been identified taking into account early drop out, continuous use of heroin, severe behavioral or psychiatric problems, misbehavior and diversion during the 6 months treatment period. No difference was evidenced between responders and non-responders to BUP in the frequency of kappa opioid receptor (OPRK1) 36G>T SNP. The frequency of dopamine transporter (DAT) gene polymorphism (SLC6A3/DAT1), allele 10, was evidently much higher in "non-responder" than in "responder" individuals (64.9% vs. 55.93%) whereas the frequency of the category of other alleles (6, 7 and 11) was higher in responder than in non-responder individuals (11.02% vs. 2.13% respectively). On one hand, the hypothesis that possible gene-related changes in kappa-opioid receptor could consistently affect buprenorphine pharmacological action and clinical effectiveness was not confirmed in our study, at least in relation to the single nucleotide polymorphism 36G>T. On the other hand, the possibility that gene-related dopamine changes could have reduced BUP effectiveness and impaired maintenance treatment outcome was cautiously supported by our findings. DAT1 gene variants such as allele 10, previously reported in association with personality and behavioral problems, would have influenced the effects of BUP-induced dopamine release, modulated through mu and kappa opioid receptors, and probably the related reinforcing capacity of the drug.

Comparing methadone and buprenorphine maintenance with methadone-assisted withdrawal for the treatment of opioid dependence during pregnancy: maternal and neonatal outcomes

Pregnancy can motivate opioid-dependent women to seek substance abuse treatment. Research has demonstrated that although prenatal exposure to buprenorphine results in less severe neonatal abstinence syndrome (NAS) relative to prenatal methadone exposure, the maternal and other neonatal outcomes are similar for the two medications. Maternal and neonatal outcomes for opioid-dependent pregnant women receiving these medications have not been systematically ompared with methadone-assisted withdrawal. The present study provides an initial assessment of the relative efficacy of both methadone and buprenorphine maintenance versus methadone-assisted withdrawal in terms of neonatal and maternal delivery outcomes. Data were derived from (1) the MOTHER (Maternal Opioid Treatment: Human Experimental Research) study at the Johns Hopkins University Bayview Medical Center (JHBMC), or (2) retrospective records review of women who underwent methadone-assisted withdrawal at the JHBMC during the time period in which participants were enrolled in the MOTHER study. Compared with the methadone maintenance group, the methadone-assisted withdrawal group had a significantly lower mean NAS peak score (Means = 13.7 vs 7.0; P = 0.002), required a significantly lower mean amount of morphine to treat NAS (Means = 82.8 vs 0.2; P < 0.001), had significantly fewer days medicated for NAS (Means = 31.5 vs 3.9; P < 0.001), and remained in the hospital for a significantly fewer number of days, on average (Means = 24.2 vs 7.0; P < 0.019). Compared with the buprenorphine maintenance group, the methadone-assisted withdrawal group required a significantly lower mean amount of morphine to treat NAS (Means = 8.2 vs 0.2; P < 0.001) and significantly fewer days medicated for NAS (Means = 12.0 vs 3.9; P = 0.008). Findings suggest that it is possible for some opioid-dependent pregnant women to succeed with methadone-assisted withdrawal. Future research needs to more fully evaluate the potential benefits and risks of methadone-assisted withdrawal for the maternal-fetal dyad.

Differential antinociceptive effects of buprenorphine and methadone in the presence of HIV-gp120

BACKGROUND

We showed recently that elevated brain levels of the chemokine stromal cell-derived growth factor-1α (SDF-1α/CXCL12, a ligand for the human immunodeficiency virus [HIV] co-receptor CXCR4) diminish the antinociceptive effect of morphine, but failed to influence buprenorphine-induced antinociception.

AIMS

Because the HIV-1 coat protein, glycoprotein 120 (gp120) T-tropic strain, binds to the same receptor as SDF-1α/CXCL12, the present experiments were designed to investigate the consequence of administering gp120 to rat brain on buprenorphine-induced antinociception in the 54°C hot plate test. For comparative purposes, the effect of gp120 on an equi-antinociceptive dose of methadone was also examined.

METHODS

A sterilized stainless-steel C313G guide cannula was implanted into the periaqueductal grey (PAG), a brain region critical for the processing of pain signals, and a primary site of action of many analgesics. Rats were pretreated with gp120, administered into the PAG.

RESULTS

The subsequent antinociception associated with methadone was diminished whereas buprenorphine-induced antinociception was unaffected. Buprenorphine thus appears to be a more effective analgesic than methadone in the presence of gp120 in the brain, a condition that is associated with HIV-related pain and infection.

Prenatal exposure to methadone and buprenorphine: a review of the potential effects on cognitive development

The amount of opioid users receiving opioid maintenance therapy has increased significantly over the last few years. As a result, an increasing number of children are prenatally exposed to long-lasting opioids such as methadone and buprenorphine. This article reviews the literature on the cognitive development of children born to mothers in opioid maintenance therapy. Topics discussed are the effects of prenatal exposure on prematurity, somatic growth, brain volume, myelination, and the endocrine and neurotransmitter system. Social-environmental factors, including parental functioning, as well as genetic factors are also described. Areas requiring further research are identified.

Buprenorphine: a unique drug with complex pharmacology

Buprenorphine, an opioid with mixed agonist-antagonist activity at classical opioid receptors, has been approved recently for the treatment of opioid dependency. Buprenorphine is also used as an analgesic. The buprenorphine dose-response curve is sometimes submaximal, or even bell-shaped, in nociceptive assays, depending upon the nature and intensity of the noxious stimulus. Moreover, buprenorphine, when administered with full agonists, such as morphine, antagonizes the action of these drugs. Partial agonism at the mu opioid receptor and, in some cases, antagonism at the kappa or delta opioid receptor have been considered as possible underlying mechanisms for the ceiling effect and bell-shaped dose-response curve of buprenorphine. While ceiling effects can be explained by partial agonist activity of buprenorphine, the bell-shaped dose-response curve cannot be a consequence of this property of the drug. Recently, buprenorphine has been shown to activate the opioid receptor-like (ORL-1; also known as NOP) receptor. Supraspinal activation of the ORL-1 receptor counteracts the antinociceptive and rewarding actions of morphine, raising the possibility that these actions of buprenorphine can also be altered by its ability to concomitantly activate the ORL-1 receptor. The use of molecular biological techniques has advanced our knowledge regarding the role of opioid receptors in modulation of pain and reward. In particular, generation of opioid receptor knockout mice has proven useful in this regard. Indeed, using knockout mice, we have recently shown that the antinociceptive effect of buprenorphine mediated primarily by the mu opioid receptor is attenuated by the ability of the drug to activate the ORL-1 receptor. Thus, the goal of this review is to provide evidence demonstrating that the ORL-1 receptor plays a functional role not only in the antinociceptive effect of buprenorphine but also in other actions of the drug as well.

Analgesic efficacy of buprenorphine in the presence of high levels of SDF-1α/CXCL12 in the brain

Although morphine is often the best option for treating acute and chronic severe pain, its analgesic activity can be blocked in situations in which there are elevated levels of chemokines. Indeed, recently we have shown that elevated brain levels of the chemokine stromal cell-derived growth factor-1alpha (SDF-1α/CXCL12, the ligand of the HIV co-receptor CXCR4) diminish the antinociceptive effect of morphine. The purpose of the present study was to investigate whether such an effect is restricted to morphine or extends to other opioid medications such as buprenorphine. A sterilized stainless-steel C313G guide cannula was implanted into the periaqueductal grey (PAG), a brain region critical to the processing of pain signals, and a primary site of action of many analgesic compounds. The cold-water (-3°C) tail-flick test (CWT) was used to measure antinociception. Rats were pretreated with SDF-1α/CXCL12 administered into the PAG, and the antinociceptive actions of buprenorphine were measured. Direct infusion of SDF-1α/CXCL12 into the PAG failed to alter the antinociceptive action of buprenorphine. The presence of SDF-1α/CXCL12 in the PAG differentially alters the antinociceptive function of opioid medications. While it was able to diminish the antinociception induced by morphine (Adler et al., 2006), SDF-1α/CXCL12 did not affect the buprenorphine-induced antinociception. Buprenorphine appears to be more effective in the presence of high levels of SDF-1α/CXCL12 in the brain (which frequently occurs during neuroinflammatory conditions).

Buprenorphine and buprenorphine/naloxone diversion, misuse, and illicit use: an international review

The diversion, misuse, and non-medically supervised use of buprenorphine and buprenorphine/naloxone by opioid users are reviewed. Buprenorphine and buprenorphine/naloxone are used globally as opioid analgesics and in the treatment of opioid dependency. Diversion of buprenorphine and buprenorphine/naloxone represents a complex medical and social issue, and has been widely documented in various geographical regions throughout the world. We first discuss the clinical properties of buprenorphine and its abuse potential. Second, we discuss its diversion and illicit use on an international level, as well as motivations for those activities. Third, we examine the medical risks and benefits of buprenorphine's non-medically supervised use and misuse. These risks and benefits include the effect of buprenorphine's use on HIV risk and the risk of its concomitant use with other medications and drugs of abuse. Finally, we discuss the implications of diversion, misuse, and non-medically supervised use (including potential measures to address issues of diversion); and potential areas for further research.

Tolerance and withdrawal from prolonged opioid use in critically ill children

OBJECTIVE

After prolonged opioid exposure, children develop opioid-induced hyperalgesia, tolerance, and withdrawal. Strategies for prevention and management should be based on the mechanisms of opioid tolerance and withdrawal.

PATIENTS AND METHODS

Relevant manuscripts published in the English language were searched in Medline by using search terms "opioid," "opiate," "sedation," "analgesia," "child," "infant-newborn," "tolerance," "dependency," "withdrawal," "analgesic," "receptor," and "individual opioid drugs." Clinical and preclinical studies were reviewed for data synthesis.

RESULTS

Mechanisms of opioid-induced hyperalgesia and tolerance suggest important drug- and patient-related risk factors that lead to tolerance and withdrawal. Opioid tolerance occurs earlier in the younger age groups, develops commonly during critical illness, and results more frequently from prolonged intravenous infusions of short-acting opioids. Treatment options include slowly tapering opioid doses, switching to longer-acting opioids, or specifically treating the symptoms of opioid withdrawal. Novel therapies may also include blocking the mechanisms of opioid tolerance, which would enhance the safety and effectiveness of opioid analgesia.

CONCLUSIONS

Opioid tolerance and withdrawal occur frequently in critically ill children. Novel insights into opioid receptor physiology and cellular biochemical changes will inform scientific approaches for the use of opioid analgesia and the prevention of opioid tolerance and withdrawal.

Chronic in utero buprenorphine exposure causes prolonged respiratory effects in the guinea pig neonate

Our laboratory studies the effects of in utero opioid exposure on the neonate. In this work we test the effects of chronic in utero exposure to buprenorphine on the neonate. Buprenorphine is a promising candidate for treatment of opioid addiction during pregnancy and it has been suggested to decrease the neonatal abstinence syndrome in human infants. In our guinea pig model, we focused not only on the respiratory effects of in utero exposure on the neonate, but also studied withdrawal signs in the neonate, a major concern of all opioid treatment during pregnancy. Pregnant guinea pigs were treated with daily subcutaneous injections of 0.1mg/kg buprenorphine during the second half of gestation. We measured weight, locomotor activity and respiratory function in pups of ages 3 to 14 days. Respiratory response was recorded using a two-chamber plethysmograph, while pups were breathing either room air or 5% CO(2). Our results show that chronic in utero exposure to buprenorphine induces respiratory effects up to day 14 after birth, while earlier studies have shown that effects of either in utero methadone or morphine only persist in the first week after birth in the guinea pig model. These data provide important information for clinical trials of buprenorphine treatment suggesting that duration and severity of respiratory effects of in utero buprenorphine exposure should be monitored.

Opioid addiction and pregnancy: perinatal exposure to buprenorphine affects myelination in the developing brain

Buprenorphine is a mu-opioid receptor partial agonist and kappa-opioid receptor antagonist currently on trials for the management of pregnant opioid-dependent addicts. However, little is known about the effects of buprenorphine on brain development. Oligodendrocytes express opioid receptors in a developmentally regulated manner and thus, it is logical to hypothesize that perinatal exposure to buprenorphine could affect myelination. To investigate this possibility, pregnant rats were implanted with minipumps to deliver buprenorphine at 0.3 or 1 mg/kg/day. Analysis of their pups at different postnatal ages indicated that exposure to 0.3 mg/kg/day buprenorphine caused an accelerated and significant increase in the brain expression of all myelin basic protein (MBP) splicing isoforms. In contrast, treatment with the higher dose caused a developmental delay in MBP expression. Examination of corpus callosum at 26-days of age indicated that both buprenorphine doses cause a significant increase in the caliber of the myelinated axons. Surprisingly, these axons have a disproportionately thinner myelin sheath, suggesting alterations at the level of axon-glial interactions. Analysis of myelin associated glycoprotein (MAG) expression and glycosylation indicated that this molecule may play a crucial role in mediating these effects. Co-immunoprecipitation studies also suggested a mechanism involving a MAG-dependent activation of the Src-family tyrosine kinase Fyn. These results support the idea that opioid signaling plays an important role in regulating myelination in vivo and stress the need for further studies investigating potential effects of perinatal buprenorphine exposure on brain development.

Buprenorphine treatment: factors and first-hand experiences for providers to consider

The viability of using buprenorphine to treat opiate dependence was well documented prior to federal approval in October 2002. What has been lacking in the literature is "hands-on" experience of providers from a clinical management and practice management perspective. This article adds to the knowledge base by providing information about buprenorphine treatment as well as anecdotes from patients treated by the authors, leading to a detailed list of factors worth considering for the treatment provider contemplating adding an opiate-addicted population to an existing treatment base.

Simultaneous determination of methadone, buprenorphine and norbuprenorphine in biological fluids for therapeutic drug monitoring purposes

Methadone and buprenorphine are two of the drugs most frequently used for abstinence from illicit opioids and in the treatment of pain. A sensitive and selective high-performance liquid chromatographic method with diode array detection for the simultaneous determination of methadone, buprenorphine and norbuprenorphine has been developed. Separation of the three analytes was obtained by using a reversed-phase column (C8, 250mmx4.6mm i.d., 5microm) and a mobile phase composed of 40% phosphate buffer containing triethylamine, 50% methanol and 10% acetonitrile (final apparent pH 6.0). Loxapine was used as the internal standard. An accurate pre-treatment procedure of biological samples was developed, using solid-phase extraction with C8 cartridges (100mg, 1mL) and needing small amounts of plasma or urine (300microL). The calibration curves were linear over a working range of 10.0-1500.0ng/mL for methadone and of 5.0-500.0ng/mL for buprenorphine and norbuprenorphine in both matrices. The limit of quantitation (LOQ) and the limit of detection (LOD) were 1.0 and 0.4ng/mL for methadone and 0.5 and 0.2ng/mL for both buprenorphine and norbuprenorphine, respectively. The method was successfully applied to the analysis of plasma and urine samples from patients undergoing treatment with these drugs. Precision and accuracy results were satisfactory and no interference from endogenous or exogenous compounds was found. The method is suitable for the simultaneous determination of methadone and buprenorphine in human plasma and urine for therapeutic drug monitoring purposes.

The mu opioid receptor is involved in buprenorphine-induced locomotor stimulation and conditioned place preference

The analgesic effect of buprenorphine is mediated via the mu opioid receptor (MOP). In the present study, using mice lacking the MOP and their wild-type littermates, we determined the role of the MOP in buprenorphine-induced locomotor stimulation and conditioned place preference (CPP). Buprenorphine (3 mg/kg) increased motor activity in wild-type but not in MOP knockout mice, showing the motor stimulatory action of buprenorphine is mediated via the MOP. When the mice were given the same treatment once daily for 5 consecutive days and challenged with buprenorphine on day 11, the motor stimulatory action of buprenorphine was enhanced in wild-type but not in MOP knockout mice, showing sensitization developed to the motor stimulatory action of buprenorphine and this phenomenon was mediated via the MOP. Likewise, buprenorphine induced CPP in wild-type mice after four alternate-day saline/buprenorphine (3 mg/kg) injections paired with olfactory and visual cues. However, buprenorphine failed to induce CPP in MOP knockout mice. In contrast, amphetamine (1 mg/kg) induced a comparable CPP in wild-type and MOP knockout mice. Together, the present results suggest that the ability of buprenorphine to increase motor activity and induce locomotor sensitization and CPP is mediated via the MOP.

Buprenorphine-containing treatments: place in the management of opioid addiction

Although the synthetic opioid buprenorphine has been available clinically for almost 30 years, its use has only recently become much more widespread for the treatment of opioid addiction. The pharmacodynamic and pharmacokinetic profiles of buprenorphine make it unique in the armamentarium of drugs for the treatment of opioid addiction. Buprenorphine has partial mu-opioid receptor agonist activity and is a kappa-opioid receptor antagonist; hence, it can substitute for other micro-opioid receptor agonists, yet is less apt to produce overdose reactions or dysphoria. On the other hand, buprenorphine can block the effects of opioids such as heroin (diamorphine) and morphine, and can even precipitate withdrawal in individuals physically dependent upon these drugs. Buprenorphine has significant sublingual bioavailability and a long half-life, making administration on a less than daily basis possible. Furthermore, its discontinuation is associated with only a mild withdrawal syndrome. Clinical trials have demonstrated that sublingual buprenorphine is effective in both maintenance therapy and detoxification of individuals addicted to opioids. The introduction of a sublingual formulation combining naloxone with buprenorphine further reduces the risk of diversion to illicit intravenous use. Because of its relative safety and lower risk of illegal diversion, buprenorphine has been made available in several countries for treating opioid addiction in the private office setting, greatly enhancing treatment options for this condition.

Effects of monoamine oxidase inhibitors on cocaine discrimination in rats

This study tested the time course of the discriminative stimulus effects of inhibitors of monoamine oxidase alone or in combination with cocaine. Male Sprague-Dawley rats were trained to discriminate cocaine (10 mg/kg, intraperitoneal) from saline using a two-lever choice methodology. The nonselective monoamine oxidase inhibitors tranylcypromine (0.01-5 mg/kg) and phenelzine (1-25 mg/kg), the monoamine oxidase-A selective compound clorgyline (1-25 mg/kg), and the monoamine oxidase-B selective compounds pargyline (0.005-50 mg/kg) and selegiline (1-25 mg/kg) were tested for substitution 15 min or 24 h following administration, and in combination with 10 mg/kg of cocaine 24 and 48 h after administration. At 15 min, selegiline fully substituted for the discriminative stimulus effects of cocaine, whereas all other compounds partially substituted. At 24 h, substitution of cocaine was diminished for all compounds except phenelzine, which produced a greater amount of substitution at 24 h than at 15 min. When cocaine was administered 24 h after clorgyline, selegiline, pargyline, and phenelzine, cocaine-appropriate responding was attenuated at intermediate doses of these drugs, whereas the highest doses did not alter cocaine-lever responding. All compounds except selegiline substantially decreased response rate and produced various adverse effects. At 48 h, the effects of all compounds except phenelzine were markedly reduced. Selectivity for monoamine oxidase-A or monoamine oxidase-B did not predict the ability to substitute for or attenuate the subjective effects of cocaine. These findings suggest that monoamine oxidase inhibitors can modulate the discriminative stimulus effects of cocaine for at least 24 h, and may be useful for treatment of cocaine abuse.

Transdermal buprenorphine in the management of persistent pain - safety aspects

By virtue of their efficacy, opioid analgesics have long been used for the treatment of both acute and chronic pain. Concerns regarding their safety and tolerability have frequently prevented this class of drugs achieving their full therapeutic potential, and their reported association with drug abuse and dependence has led to a reduced acceptance by many patients. Indeed, there is a variety of opioid-like side effects which are common to all members of the class, but some opioids have a more favourable safety profile than others. Buprenorphine is a semisynthestic opioid with a mu-agonistic and kappa-antagonistic receptor-binding profile. Studies over the past two decades have shown buprenorphine to have a complex and unique pharmacological profile, which results in enhanced therapeutic benefits combined with a favourable safety profile. Having been underused before, the development of a new transdermal drug delivery system for buprenorphine has revived interest in this substance. Transdermal buprenorphine (Gruenenthal GmbH, Aachen, Germany) provides a noninvasive method of rate-controlled drug release ensuring constant and predictable serum buprenorphine levels over a prolonged period. This preparation has been shown to be advantageous for long-term treatment of chronic pain patients providing reliable pain control, few adverse events, and good patient acceptance.

Changes in the Prescribed Daily Doses of Transdermal Fentanyl and Transdermal Buprenorphine During Treatment of Patients with Cancer and Noncancer Pain in Germany: Results of a Retrospective Cohort Study

BACKGROUND

During long-term therapy with strong opioids (step III opioids according to the World Health Organization [WHO] analgesic ladder), dose increases are often necessary because of deterioration of the primary disease or development of tolerance.

OBJECTIVE

The purpose of this study was to compare changes in dosages of transdermal (TD) fentanyl and TD buprenorphine in patients with cancer and non-cancer pain.

METHODS

In a retrospective study, patients with cancer and noncancer pain being treated with TD fentanyl or TD buprenorphine for at least 3 months between January 2001 and December 2003 were identified from the IMS Disease Analyzer-mediplus database, which contains all patient-related data documented from 400 medical practices in Germany. The indications for treatment were defined according to the International Classification of Diseases, 10th Revision, and included neoplasm (cancer groups), and osteoarthritis, low back pain, and osteoporosis (noncancer groups). The cohort patients were considered to have comparable pain intensity because they had received similar analgesic premedication classified according to steps I to III of the WHO analgesic ladder (cohort groups). The mean prescribed daily doses on first and last prescription were documented, and the mean percentile increases were calculated over the whole treatment duration and per day. Additionally, the mean percentile intraindividual increases (on a per-patient basis) were estimated.

RESULTS

The cohort groups consisted of 448 patients with noncancer pain and 446 patients with cancer pain (552 women and 342 men; mean age, 74 years; range, 25-101 years). The mean percentile increases in dosages over the whole treatment duration and adjusted per day were significantly higher in patients taking TD fentanyl (P < 0.05). Differences were even greater for the mean percentile intraindividual increases per day, which totaled 0.42%and 0.17% for cancer patients taking TD fentanyl and TD buprenorphine, respectively; corresponding values were 0.25% and 0.09%in noncancer patients (P < 0.001).

CONCLUSIONS

This retrospective analysis showed a significantly higher increase in the mean daily doses of TD fentanyl as compared with TD buprenorphine. The results must be verified in prospective, randomized clinical studies.