Inhibition of human drug metabolizing cytochrome P450 by buprenorphine

Opioids in the Elderly Patients with Cognitive Impairment: A Narrative Review

Introduction

Assessment and management of pain in elderly people with cognitive impairment is particularly challenging. Physiological changes due to aging as well as comorbidities and polypharmacy are responsible for a complex clinical approach. Concomitantly, in cognitive impairment, including advanced dementia, changes in the central nervous system along with changes in the peripheral nervous system due to aging have a significant impact on pain perception. Sometimes clinicians decide to prescribe opioids to relieve pain, also without a clear indication. This review aims to investigate the effect of opioids in elderly patients with cognitive impairment.

Methods

A literature search of PubMed/Medline, Scopus, and Cochrane databases was conducted using keyword searches to generate lists of articles that were screened for relevance by title and abstract to give a final list of articles for full-text review. Further articles were identified by scanning the reference lists of the full-text articles.

Discussion

This review discusses the complex physiological and pharmacological changes in the elderly as well as the neurological changes that affect pain perception in this population. Additionally, it focuses on cognitive impairment and pain in Alzheimer’s disease and other dementias, the pain assessment in the elderly with cognitive impairment as well as the safety of opioid use in the elderly. Information regarding opioid prescription in nursing homes and recorded indications for opioid use, type and dosing of opioids, and compliance of treatment in advanced dementia are also provided.

Conclusions

Opioid prescription in the elderly population with cognitive impairment is particularly complex. All healthcare professionals involved in the care of such patients need to be aware of the challenges and strive to ensure analgesic use is guided by appropriate and accurate pain assessment.

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.

Nicotine biomarkers and rate of nicotine metabolism among cigarette smokers taking buprenorphine for opioid dependency

BACKGROUND

Individual differences in the rate of nicotine metabolism contribute to differences in tobacco use, dependence, and efficacy of smoking cessation treatments and can be assessed using the nicotine metabolite ratio (NMR), a validated biomarker for CYP2A6 activity. Despite the high cigarette smoking rates observed in opioid users, no data have been reported on NMR among this population as they has been largely excluded from previous studies that have examined the relationship between tobacco use characteristics and rate of nicotine metabolism.

METHODS

A linear regression model was used to examine the relationship between tobacco use characteristics and NMR among smokers taking buprenorphine for opioid dependency (N=141). The relationship between buprenorphine dose and NMR was also examined. All participants were enrolled in an intervention designed to promote cigarette-smoking cessation, though participants did not need to stop smoking to enroll.

RESULTS AND CONCLUSIONS

Rate of nicotine metabolism assessed using the NMR was positively associated with cigarettes smoked in the past 24h, but was not related to time to first cigarette or past year quit attempts. Dose of buprenorphine was not associated with NMR, suggesting no association with rate of nicotine metabolism. Our results suggest that NMR is related to tobacco use among persons enrolled in opioid treatment, as reported in general population smokers and may be a useful biomarker to include in future research assessing efficacy of tobacco cessation interventions in this population.

New developments in the management of opioid dependence: focus on sublingual buprenorphine-naloxone

Opioid maintenance therapy is a well-established first-line treatment approach in opioid dependence. Buprenorphine, a partial opioid agonist, has been found by numerous studies to be an effective and safe medication in the treatment of opioid dependence. At present, buprenorphine is available as a monodrug or in a fixed 4:1 ratio combination with naloxone. A diminished risk of diversion and abuse for the buprenorphine-naloxone combination is likely but not firmly established. Conventional formulations are given sublingually to avoid the hepatic first-pass effect. A novel film tablet is available only in the US and Australia. Other novel, sustained-release formulations (implant, depot) are currently being developed and tested. Recent studies, including a Cochrane meta-analysis, suggest that the retention with buprenorphine is lower than for methadone, but that buprenorphine may be associated with less drug use. Higher doses of buprenorphine are associated with better retention rates. Buprenorphine has a ceiling effect at the opioid receptor with regard to respiratory depression, and may cause fewer fatal intoxications than methadone. Possible antidepressant effects of buprenorphine and its use in comorbid psychiatric patients has not been studied in much detail. Clinical implications are discussed.

A review of pharmacological interactions between HIV or hepatitis C virus medications and opioid agonist therapy: implications and management for clinical practice

Global access to opioid agonist therapy and HIV/hepatitis C virus (HCV) treatment is expanding but when used concurrently, problematic pharmacokinetic and pharmacodynamic interactions may occur. Articles published from 1966 to 2012 in Medline were reviewed using the following keywords: HIV, AIDS, HIV therapy, HCV, HCV therapy, antiretroviral therapy, highly active antiretroviral therapy, drug interactions, methadone and buprenorphine. In addition, a review of abstracts from national and international meetings and conference proceedings was conducted; selected reports were reviewed as well. The metabolism of both opioid and antiretroviral therapies, description of their known interactions and clinical implications and management of these interactions were reviewed. Important pharmacokinetic and pharmacodynamic drug interactions affecting either methadone or HIV medications have been demonstrated within each class of antiretroviral agents. Drug interactions between methadone, buprenorphine and HIV medications are known and may have important clinical consequences. Clinicians must be alert to these interactions and have a basic knowledge regarding their management.

Sublingual buprenorphine/naloxone for chronic pain in at-risk patients: development and pilot test of a clinical protocol

OBJECTIVE

Sublingual buprenorphine/naloxone (Bup/Nx) is approved for addiction treatment and may be useful for pain management, particularly in opioid-treated patients with pain with nonadherence behaviors. The transition of opioid-treated patients with pain to buprenorphine carries the risk of precipitated withdrawal and increased pain. This study convened pain and addiction specialists to develop and pilot a clinical protocol for safe transitioning to Bup/Nx.

DESIGN

The protocol was revised three times based on outside expert review and pilot study observations. The pilot was conducted with a prospective cohort of 12 patients with moderate to severe chronic pain, who were receiving long-term opioid therapy with any full m-agonist drug, and had exhibited one or more aberrant drug-related behaviors. Patients were followed up for 3-6 months with the expectation that they would experience few adverse events (AEs) and report lower pain severity.

RESULTS

The three patients on the highest baseline opioid dose (equivalent to 303-450 mg of oral morphine) and the three on the lowest doses (≤20 mg) had early AEs when switched to Bup/Nx and did not complete the trial. Of the remaining six, one withdrew due to AEs; one responded well, then withdrew; and four completed a 3-month trial. A mixed-effects model controlling for dropouts found that average and worst pain significantly decreased after the switch to Bup/Nx (both p < 0.01).

CONCLUSION

Based on this experience, the protocol recommends Bup/Nx for pain only when baseline opioid doses are within bounds that reduce AEs at transition and incorporates dose flexibility to further reduce risks. This protocol warrants further testing.

Clinical pharmacology of analgesic medicines in older people: impact of frailty and cognitive impairment

Pain is highly prevalent in frail older people who often have multiple co-morbidities and multiple medicines. Rational prescribing of analgesics in frail older people is complex due to heterogeneity in drug disposition, comorbid medical conditions, polypharmacy and variability in analgesic response in this population. A critical issue in managing older people with pain is the need for judicious choice of analgesics based on a comprehensive medical and medication history. Care is needed in the selection of analgesic medicine to avoid drug-drug or drug-disease interactions. People living with dementia and cognitive impairment have suboptimal pain relief which in part may be related to altered pharmacodynamics of analgesics and challenges in the systematic assessment of pain intensity in this patient group. In the absence of rigorously controlled trials in frail older people and those with cognitive impairment a pharmacologically-guided approach can be used to optimize pain management which requires a systematic understanding of the pharmacokinetics and pharmacodynamics of analgesics in frail older people with or without changes in cognition.

Pharmacokinetic drug interactions and adverse consequences between psychotropic medications and pharmacotherapy for the treatment of opioid dependence

BACKGROUND

Psychiatric comorbidities among opioid-dependent patients are common. Many medications used to treat both conditions are metabolized through complimentary cytochrome P450 isoenzymes. When medication-assisted treatment for opioid dependence is concurrently used with psychotropic medications, problematic pharmacokinetic drug interactions may occur.

METHODS

We reviewed relevant English language articles identified through the MedLine, Scopus, and Embase databases from 1950 to December 2009 using the specific generic names of medications and keywords such as pharmacokinetics and drug interactions with buprenorphine, methadone, and naltrexone. Selected references from these articles were reviewed. Additionally, a review was conducted of abstracts and conference proceedings from national and international meetings from 1990 to 2009. A total of 60 studies were identified and reviewed.

RESULTS

Clinical case series and carefully controlled pharmacokinetic interaction studies have been conducted between methadone, buprenorphine, or naltrexone and some psychoactive medications. Important pharmacokinetic drug interactions have been demonstrated within each class of medications affecting either methadone and buprenorphine or psychoactive drugs. Few studies, however, have been conducted with naltrexone.

CONCLUSIONS

Several interactions between methadone, buprenorphine, or naltrexone and psychoactive medications are described and may have important clinical consequences. To optimize care, clinicians must be alerted to these interactions.

Sustained release d-amphetamine reduces cocaine but not 'speedball'-seeking in buprenorphine-maintained volunteers: a test of dual-agonist pharmacotherapy for cocaine/heroin polydrug abusers

The aim of this study was to determine whether oral sustained release d-amphetamine (SR-AMP) reduces cocaine and opioid/cocaine combination ('speedball'-like) seeking in volunteers with current opioid dependence and cocaine dependence. Following outpatient buprenorphine (BUP) 8 mg/day stabilization without SR-AMP, eight participants completed a 3-week in-patient study with continued BUP 8 mg/day maintenance and double-blind ascending SR-AMP weekly doses of 0, 30, and 60 mg/day, respectively. After 3 days (Saturday-Monday) stabilization at each SR-AMP weekly dose (0, 15, or 30 mg administered at 0700 and 1225 each day), on Tuesday-Friday mornings (0900-1200 hours), participants sampled four drug combinations in randomized, counterbalanced order under double-blind, double-dummy (intranasal cocaine and intramuscular hydromorphone) conditions: cocaine (COC 100 mg+saline); hydromorphone (COC 4 mg+HYD 24 mg); 'speedball' (COC 100 mg+HYD 24 mg); and placebo (COC 4 mg+saline). Subjective and physiological effects of these drug combinations were measured. From 1230 to 1530 hours, participants could respond on a choice, 12-trial progressive ratio schedule to earn drug units (1/12th of total morning dose) or money units (US$2). SR-AMP significantly reduced COC, but not HYD or speedball, choices and breakpoints. SR-AMP also significantly reduced COC subjective (eg, abuse-related) effects and did not potentiate COC-induced cardiovascular responses. This study shows the ability of SR-AMP to attenuate COC self-administration, as well as its selectivity, in cocaine/heroin polydrug abusers. Further research is warranted to ascertain whether SR-AMP combined with BUP could be a useful dual-agonist pharmacotherapy.

Management of chronic pain in the elderly: focus on transdermal buprenorphine

Chronic pain in the elderly is a significant problem. Pharmacokinetic and metabolic changes associated with increased age makes the elderly vulnerable to side effects and overdosing associated with analgesic agents. Therefore the management of chronic cancer pain and chronic nonmalignant pain in this growing population is an ongoing challenge. New routes of administration have opened up new treatment options to meet this challenge. The transdermal buprenorphine matrix allows for slow release of buprenorphine and damage does not produce dose dumping. In addition the long-acting analgesic property and relative safety profile makes it a suitable choice for the treatment of chronic pain in the elderly. Its safe use in the presence of renal failure makes it an attractive choice for older individuals. Recent scientific studies have shown no evidence of a ceiling dose of analgesia in man but only a ceiling effect for respiratory depression, increasing its safety profile. It appears that transdermal buprenorphine can be used in clinical practice safely and efficaciously for treating chronic pain in the elderly.

Pharmacogenetics of analgesics: toward the individualization of prescription

The use of analgesics is based on the empiric administration of a given drug with clinical monitoring for efficacy and toxicity. However, individual responses to drugs are influenced by a combination of pharmacokinetic and pharmacodynamic factors that can sometimes be regulated by genetic factors. Whereas polymorphic drug-metabolizing enzymes and drug transporters may affect the pharmacokinetics of drugs, polymorphic drug targets and disease-related pathways may influence the pharmacodynamic action of drugs. After a usual dose, variations in drug toxicity and inefficacy can be observed depending on the polymorphism, the analgesic considered and the presence or absence of active metabolites. For opioids, the most studied being morphine, mutations in the ABCB1 gene, coding for P-glycoprotein (P-gp), and in the µ-opioid receptor reduce morphine potency. Cytochrome P450 (CYP) 2D6 mutations influence the analgesic effect of codeine and tramadol, and polymorphism of CYP2C9 is potentially linked to an increase in nonsteroidal anti-inflammatory drug-induced adverse events. Furthermore, drug interactions can mimic genetic deficiency and contribute to the variability in response to analgesics. This review summarizes the available data on the pharmacokinetic and pharmacodynamic consequences of known polymorphisms of drug-metabolizing enzymes, drug transporters, drug targets and other nonopioid biological systems on central and peripheral analgesics.

Opioids and the management of chronic severe pain in the elderly: consensus statement of an International Expert Panel with focus on the six clinically most often used World Health Organization Step III opioids (buprenorphine, fentanyl, hydromorphone, methadone, morphine, oxycodone)

SUMMARY OF CONSENSUS: 1. The use of opioids in cancer pain: The criteria for selecting analgesics for pain treatment in the elderly include, but are not limited to, overall efficacy, overall side-effect profile, onset of action, drug interactions, abuse potential, and practical issues, such as cost and availability of the drug, as well as the severity and type of pain (nociceptive, acute/chronic, etc.). At any given time, the order of choice in the decision-making process can change. This consensus is based on evidence-based literature (extended data are not included and chronic, extended-release opioids are not covered). There are various driving factors relating to prescribing medication, including availability of the compound and cost, which may, at times, be the main driving factor. The transdermal formulation of buprenorphine is available in most European countries, particularly those with high opioid usage, with the exception of France; however, the availability of the sublingual formulation of buprenorphine in Europe is limited, as it is marketed in only a few countries, including Germany and Belgium. The opioid patch is experimental at present in U.S.A. and the sublingual formulation has dispensing restrictions, therefore, its use is limited. It is evident that the population pyramid is upturned. Globally, there is going to be an older population that needs to be cared for in the future. This older population has expectations in life, in that a retiree is no longer an individual who decreases their lifestyle activities. The "baby-boomers" in their 60s and 70s are "baby zoomers"; they want to have a functional active lifestyle. They are willing to make trade-offs regarding treatment choices and understand that they may experience pain, providing that can have increased quality of life and functionality. Therefore, comorbidities--including cancer and noncancer pain, osteoarthritis, rheumatoid arthritis, and postherpetic neuralgia--and patient functional status need to be taken carefully into account when addressing pain in the elderly. World Health Organization step III opioids are the mainstay of pain treatment for cancer patients and morphine has been the most commonly used for decades. In general, high level evidence data (Ib or IIb) exist, although many studies have included only few patients. Based on these studies, all opioids are considered effective in cancer pain management (although parts of cancer pain are not or only partially opioid sensitive), but no well-designed specific studies in the elderly cancer patient are available. Of the 2 opioids that are available in transdermal formulation--fentanyl and buprenorphine--fentanyl is the most investigated, but based on the published data both seem to be effective, with low toxicity and good tolerability profiles, especially at low doses. 2. The use of opioids in noncancer-related pain: Evidence is growing that opioids are efficacious in noncancer pain (treatment data mostly level Ib or IIb), but need individual dose titration and consideration of the respective tolerability profiles. Again no specific studies in the elderly have been performed, but it can be concluded that opioids have shown efficacy in noncancer pain, which is often due to diseases typical for an elderly population. When it is not clear which drugs and which regimes are superior in terms of maintaining analgesic efficacy, the appropriate drug should be chosen based on safety and tolerability considerations. Evidence-based medicine, which has been incorporated into best clinical practice guidelines, should serve as a foundation for the decision-making processes in patient care; however, in practice, the art of medicine is realized when we individualize care to the patient. This strikes a balance between the evidence-based medicine and anecdotal experience. Factual recommendations and expert opinion both have a value when applying guidelines in clinical practice. 3. The use of opioids in neuropathic pain: The role of opioids in neuropathic pain has been under debate in the past but is nowadays more and more accepted; however, higher opioid doses are often needed for neuropathic pain than for nociceptive pain. Most of the treatment data are level II or III, and suggest that incorporation of opioids earlier on might be beneficial. Buprenorphine shows a distinct benefit in improving neuropathic pain symptoms, which is considered a result of its specific pharmacological profile. 4. The use of opioids in elderly patients with impaired hepatic and renal function: Functional impairment of excretory organs is common in the elderly, especially with respect to renal function. For all opioids except buprenorphine, half-life of the active drug and metabolites is increased in the elderly and in patients with renal dysfunction. It is, therefore, recommended that--except for buprenorphine--doses be reduced, a longer time interval be used between doses, and creatinine clearance be monitored. Thus, buprenorphine appears to be the top-line choice for opioid treatment in the elderly. 5. Opioids and respiratory depression: Respiratory depression is a significant threat for opioid-treated patients with underlying pulmonary condition or receiving concomitant central nervous system (CNS) drugs associated with hypoventilation. Not all opioids show equal effects on respiratory depression: buprenorphine is the only opioid demonstrating a ceiling for respiratory depression when used without other CNS depressants. The different features of opioids regarding respiratory effects should be considered when treating patients at risk for respiratory problems, therefore careful dosing must be maintained. 6. Opioids and immunosuppression: Age is related to a gradual decline in the immune system: immunosenescence, which is associated with increased morbidity and mortality from infectious diseases, autoimmune diseases, and cancer, and decreased efficacy of immunotherapy, such as vaccination. The clinical relevance of the immunosuppressant effects of opioids in the elderly is not fully understood, and pain itself may also cause immunosuppression. Providing adequate analgesia can be achieved without significant adverse events, opioids with minimal immunosuppressive characteristics should be used in the elderly. The immunosuppressive effects of most opioids are poorly described and this is one of the problems in assessing true effect of the opioid spectrum, but there is some indication that higher doses of opioids correlate with increased immunosuppressant effects. Taking into consideration all the very limited available evidence from preclinical and clinical work, buprenorphine can be recommended, while morphine and fentanyl cannot. 7. Safety and tolerability profile of opioids: The adverse event profile varies greatly between opioids. As the consequences of adverse events in the elderly can be serious, agents should be used that have a good tolerability profile (especially regarding CNS and gastrointestinal effects) and that are as safe as possible in overdose especially regarding effects on respiration. Slow dose titration helps to reduce the incidence of typical initial adverse events such as nausea and vomiting. Sustained release preparations, including transdermal formulations, increase patient compliance.

OPC-67683, a nitro-dihydro-imidazooxazole derivative with promising action against tuberculosis in vitro and in mice

BACKGROUND

Tuberculosis (TB) is still a leading cause of death worldwide. Almost a third of the world's population is infected with TB bacilli, and each year approximately 8 million people develop active TB and 2 million die as a result. Today's TB treatment, which dates back to the 1970s, is long and burdensome, requiring at least 6 mo of multidrug chemotherapy. The situation is further compounded by the emergence of multidrug-resistant TB (MDR-TB) and by the infection's lethal synergy with HIV/AIDS. Global health and philanthropic organizations are now pleading for new drug interventions that can address these unmet needs in TB treatment.

METHODS AND FINDINGS

Here we report OPC-67683, a nitro-dihydro-imidazooxazole derivative that was screened to help combat the unmet needs in TB treatment. The compound is a mycolic acid biosynthesis inhibitor found to be free of mutagenicity and to possess highly potent activity against TB, including MDR-TB, as shown by its exceptionally low minimum inhibitory concentration (MIC) range of 0.006-0.024 microg/ml in vitro and highly effective therapeutic activity at low doses in vivo. Additionally, the results of the post-antibiotic effect of OPC-67683 on intracellular Mycobacterium tuberculosis showed the agent to be highly and dose-dependently active also against intracellular M. tuberculosis H37Rv after a 4-h pulsed exposure, and this activity at a concentration of 0.1 microg/ml was similar to that of the first-line drug rifampicin (RFP) at a concentration of 3 microg/ml. The combination of OPC-67683 with RFP and pyrazinamide (PZA) exhibited a remarkably quicker eradication (by at least 2 mo) of viable TB bacilli in the lung in comparison with the standard regimen consisting of RFP, isoniazid (INH), ethambutol (EB), and PZA. Furthermore, OPC-67683 was not affected by nor did it affect the activity of liver microsome enzymes, suggesting the possibility for OPC-67683 to be used in combination with drugs, including anti-retrovirals, that induce or are metabolized by cytochrome P450 enzymes.

CONCLUSIONS

We concluded that based on these properties OPC-67683 has the potential to be used as a TB drug to help combat the unmet needs in TB treatment.

Buprenorphine: clinical pharmacokinetics in the treatment of opioid dependence

Buprenorphine is a semi-synthetic opioid derived from thebaine, a naturally occurring alkaloid of the opium poppy, Papaver somniferum. The pharmacology of buprenorphine is unique in that it is a partial agonist at the opioid mu receptor. Buprenorphine undergoes extensive first-pass metabolism and therefore has very low oral bioavailability; however, its bioavailability sublingually is extensive enough to make this a feasible route of administration for the treatment of opioid dependence. The mean time to maximum plasma concentration following sublingual administration is variable, ranging from 40 minutes to 3.5 hours. Buprenorphine has a large volume of distribution and is highly protein bound (96%). It is extensively metabolised by N-dealkylation to norbuprenorphine primarily through cytochrome P450 (CYP) 3A4. The terminal elimination half-life of buprenorphine is long and there is considerable variation in reported values (mean values ranging from 3 to 44 hours). Most of a dose of buprenorphine is eliminated in the faeces, with approximately 10-30% excreted in urine. Naloxone has been added to a sublingual formulation of buprenorphine to reduce the abuse liability of the product. The presence of naloxone does not appear to influence the pharmacokinetics of buprenorphine. Buprenorphine crosses the placenta during pregnancy and also crosses into breast milk. Buprenorphine dosage does not need to be significantly adjusted in patients with renal impairment; however, since CYP3A activity may be decreased in patients with severe chronic liver disease, it is possible that the metabolism of buprenorphine will be altered in these patients. Although there is limited evidence in the literature to date, drugs that are known to inhibit or induce CYP3A4 have the potential to diminish or enhance buprenorphine N-dealkylation. It appears that the interaction between buprenorphine and benzodiazepines is more likely to be a pharmacodynamic (additive or synergistic) than a pharmacokinetic interaction. The relationship between buprenorphine plasma concentration and response in the treatment of opioid dependence has not been well studied. The pharmacokinetic and pharmacodynamic properties of buprenorphine allow it to be a feasible option for substitution therapy in the treatment of opioid dependence.

Pharmacokinetic drug interactions between opioid agonist therapy and antiretroviral medications: implications and management for clinical practice

BACKGROUND

Opioid dependence and HIV/AIDS are 2 of the most serious yet treatable diseases worldwide. Global access to opioid agonist therapy and HIV treatment is expanding but when concurrently used, problematic pharmacokinetic drug interactions can occur.

METHODS

We reviewed English, Spanish, French, and Italian language articles from 1966 to 2005 in Medline using the following keywords: HIV, AIDS, HIV therapy, antiretroviral therapy, HAART, drug interactions, methadone, and buprenorphine. Additionally, we reviewed abstracts from national and international meetings and conference proceedings. Selected references from these articles were reviewed as well.

RESULTS

Clinical case series and carefully controlled pharmacokinetic interaction studies have been conducted between methadone and most approved antiretroviral therapies. Important pharmacokinetic drug interactions have been demonstrated within each class of agents, affecting either methadone or antiretroviral agents. Few studies, however, have been conducted with buprenorphine. The metabolism of both therapies, description of the known interactions, and clinical implications and management of these interactions are reviewed.

CONCLUSIONS

Certain interactions between methadone and antiretroviral medications are known and may have important clinical consequences. To optimize care, clinicians must be alert to these interactions and have a basic knowledge regarding their management.

Buprenorphine in cancer pain

Buprenorphine is a broad spectrum, highly lipophilic, and long-acting partial mu opioid receptor agonist that is noncross tolerant to other opioids. Buprenorphine can be given by several routes. Metabolism is through CYP3A4 and CYP2C8 and by conjugases. Constipation and sexual dysfunction appear to be less with buprenorphine than with other opioids. The recent development of a polymer matrix patch delivery system for buprenorphine prevents "dose dumping" and facilitates pain management in those unable to take oral analgesics. Sublingual buprenorphine has been combined with naloxone to prevent illicit conversion to parenteral administration. Buprenorphine has been used extensively to control cancer pain. In certain clinical situations, buprenorphine may have particular advantages over other opioids.

Flunitrazepam does not alter cerebral distribution of buprenorphine in the rat

Deaths have been reported among heroin addicts related to combined buprenorphine and flunitrazepam use. The aim of this study was to determine the existence of a drug-drug interaction during the distribution phase of buprenorphine. Arterial blood gases were measured after intravenous administration of buprenorphine alone (30 mg/kg), flunitrazepam alone (40 mg/kg) or both drugs in rats. Buprenorphine kinetics was studied in plasma and in striatum using cerebral microdialysis, both alone and after rat pretreatment with flunitrazepam. In contrast to buprenorphine or flunitrazepam alone, buprenorphine in combination with flunitrazepam induced a significant, rapid and sustained respiratory depression. Arterial PCO2 was increased at 1.5 min (6.7+/-0.2 versus 5.4+/-0.3 and 5.5+/-0.3 kPa, respectively, P=0.04) (mean+/-S.E.M.), and arterial pH decreased (7.37+/-0.02 versus 7.45+/-0.02 and 7.45+/-0.01, respectively, P=0.03). Plasma buprenorphine kinetics was well described by a three-compartment linear model, with a distribution half-life of 7.4+/-2.7 min and an elimination half-life of 463.9+/-152.3 min. However, neither plasma nor striatal buprenorphine kinetics were significantly altered by pre-administration of flunitrazepam. The adverse interaction between flunitrazepam and buprenorphine cannot be explained by a pharmacokinetic drug-drug interaction during the distribution phase of buprenorphine.

Mood and affect during detoxification of opiate addicts: a comparison of buprenorphine versus methadone

Twenty-six in-patients with Diagnostic and Statistical Manual version IV (DSM-IV) criteria for opioid dependence were selected at random to receive either a combination of an 11-day low-dose buprenorphine and a 14-day carbamazepine regimen (n = 14) or a combination of an 11-day methadone and a 14-day carbamazepine regimen (n = 12) in a double-blind, randomized 14-day in-patient detoxification treatment. Patients with buprenorphine and carbamazepine showed a significantly better psychological state after the first and second weeks of treatment. Above all, the buprenorphine-treated patients demonstrated a less marked tiredness, sensitiveness and depressive state as well as a more prominent elevated mood during the detoxification process. Seven non-completers (after 7 days: four of 12 = 33.3%; after 14 days: seven of 12 = 58.3%) were treated with methadone and carbamazepine and five non-completers (after 7 days: two of 14 = 14.3%; after 14 days: five of 14 = 35.7%) received buprenorphine and carbamazepine. The difference in the overall dropout rate after day 14 was not significant. The present study supports the hypothesis that the combination of buprenorphine and carbamazepine leads to a better clinical outcome than does a combination of methadone and carbamazepine in the detoxification of opioid addicts with additional multiple drug abuse. The buprenorphine and carbamazepine-regimen provides a more effective short-term relief of affective disturbances than does methadone and carbamazepine. No severe side effects occurred during the treatment period in both groups.

Effect of Nonspecific Binding to Microsomes and Metabolic Elimination of Buprenorphine on the Inhibition of Cytochrome P4502D6

Recently, the pharmaceutical industry has employed the high-throughput method for the evaluation of cytochrome P450 (CYP) inhibition, using a combination of the heterologously expressed enzyme and a fluoregenic substrate. When buprenorphine (BN), a potent mixed agonist-antagonist analgesic, was evaluated by this method, it exhibited potent inhibition of CYP2D6 with an IC50 value of 0.25 microM in recombinant CYP2D6-expressing insect cell microsomes (rCYP2D6 microsomes). In contrast, the IC50 value was 22.7 microM in human liver microsomes (HLM) using a classical method. Although the substrate concentrations in each study were set to near the Km values, there was a large discrepancy in IC50 values. When we investigated the effect of nonspecific binding to microsomes on the inhibitory potency, with a view to clarifying this discrepancy, the unbound fraction in microsomes (fu,mic) was 0.06-0.21 and 0.99 in HLM and rCYP2D6 microsomes, respectively. The corrected IC50 value (1.74 microM) using free BN concentrations was much smaller than the uncorrected value. On the other hand, it was observed that the concentration of BN in HLM decreased rapidly due to metabolism by CYP3A4 while that in rCYP2D6 microsomes decreased only slightly. We then investigated the effect of incubation time on the inhibitory potency, since the rapid elimination of BN in HLM could have been a cause of the discrepancy. The IC50 value for BN was observed to decrease slightly from 22.7 to 17.1 microM, following the shortening of the incubation time from 10 to 2 min in HLM. We conclude that nonspecific binding to microsomes of the inhibitor could affect the inhibitory potency against CYP2D6. If this factor is considered, a more precise estimate of the risk of adverse drug interaction could be achieved.

Buprenorphine in the treatment of opiate dependence: its pharmacology and social context of use in the U.S

Buprenorphine's physiological effects are produced when it attaches to specific opiate receptors that are designated mu, kappa, or delta. Buprenorphine, a partial agonist at the mu receptor and an antagonist at the kappa receptor, produces typical morphine-like effects at low doses. At higher doses, it produces opiate effects that are less than those of full opiate agonists. Knowledge of the physiological effects of opiate receptors and the way they interact with opiate agonists, partial opiate agonists, and opiate antagonists is fundamental to understanding the safety and efficacy of buprenorphine in treatment of pain and opiate addiction. Knowledge of the historical and social context of opiate agonist treatment of opiate dependence is fundamental to understanding how nonpharmacological factors may limit the clinical adoption and utility of a safe and effective medication in treatment of opiate dependence. This article reviews the pharmacology of sublingual buprenorphine and the historical context of opiate agonist therapy; delineates classes of opiate receptors and their interaction with opiate agonists, partial agonists, and antagonists; and describes the commercially available pharmaceutical formulations of buprenorphine. It focuses on sublingual buprenorphine tablets, Subutex and Suboxone, the FDA-approved formulations of buprenorphine for treatment of opiate dependence. Sublingual buprenorphine, and the combination of sublingual buprenorphine/naloxone, have unique pharmacological properties that make them a logical first-line intervention in the treatment of opioid dependence.

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation. condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2002 to June 2003 is reviewed, with 568 references cited.

Interaction of buprenorphine and its metabolite norbuprenorphine with cytochromes p450 in vitro

Buprenorphine is a thebaine derivative used in the treatment of heroin and other opiate addictions. In this study, the selective probe reactions for each of the major hepatic cytochromes P450 (P450s) were used to evaluate the effect of buprenorphine and its main metabolite norbuprenorphine on the activity of these P450s. The index reactions used were CYP1A2 (phenacetin O-deethylation), CYP2A6 (coumarin 7-hydroxylation), CYP2C9 (diclofenac 4'-hydroxylation), CYP2C19 (omeprazole 5-hydrxoylation), CYP2D6 (dextromethorphan O-demethylation), CYP2B6 (7-ethoxy-4-trifluoromethyl-coumarin 7-deethylation), CYP2E1 (chlorzoxazone 6-hydroxylation), and CYP3A4 (omeprazole sulfoxidation). Buprenorphine exhibited potent, competitive inhibition of CYP2D6 (Ki 10 +/- 2 microM and 1.8 +/- 0.2 microM) and CYP3A4 (Ki 40 +/- 1.6 microM and 19 +/- 1.2 microM) in microsomes from human liver and cDNA-expressing lymphoblasts, respectively. Compared with buprenorphine, norbuprenorphine demonstrated a lower inhibitory potency with CYP2D6 (22.4% inhibition at 20 microM norbuprenorphine) and CYP3A4 (13.6% inhibition at 20 microM) in microsomes from human cDNA-expressing lymphoblast cells. Furthermore, buprenorphine was shown to be a substrate of CYP2D6 (Km = 600 microM; Vmax = 0.40 nmol/min/mg protein) and CYP3A4 (Km = 36 microM; Vmax = 0.19 nmol/min/mg protein). The present in vitro study suggests that buprenorphine and its major metabolite norbuprenorphine are inhibitors of CYP2D6 and CYP3A4; however, at therapeutic concentrations they are not predicted to cause potentially clinically important drug interactions with other drugs metabolized by major hepatic P450s.