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

Opioid toxicity due to CNS depressant polypharmacy: A case report

The interaction between methadone and central nervous system depressants can cause serious adverse effects, including profound sedation, respiratory depression, coma, and death. This poses a challenge in the treatment of patients with concurrent psychiatric and substance use disorders as the combined use is often unavoidable. We report a case of a patient with opioid use disorder, mood disorder unspecified, chronic pain, and chronic obstructive pulmonary disease who experienced 2 serious episodes of CNS and respiratory depression due to polypharmacy-induced opioid toxicity. Careful consideration of pharmacokinetics, pharmacodynamics, and patient-specific factors was imperative to identify the suspected contributing medications: methadone, lorazepam, divalproex, gabapentin, and cyclobenzaprine. Cognitive and system factors that contributed to these adverse events and strategies to mitigate risk of recurrence were also identified.

Medications for Treatment of Opioid Use Disorder among Persons Living with HIV

PURPOSE OF REVIEW

Recent HIV outbreaks have occurred as a result of the current US opioid epidemic. Providing medications for opioid use disorder (MOUD) with methadone, buprenorphine, and extended-release naltrexone is essential to achieving optimal HIV treatment outcomes including viral suppression and retention in treatment. This review describes the pharmacology of MOUD with specific attention to interactions with antiretroviral therapy, and to the effect of MOUD on HIV treatment outcomes.

RECENT FINDINGS

Methadone and buprenorphine both improve HIV viral suppression, adherence to antiretroviral therapy, and overall mortality for persons with opioid use disorder (OUD). Extended-release naltrexone has been most extensively studied in persons with HIV leaving incarcerated settings, and improves HIV viral suppression in that context. Strategies that integrate MOUD and HIV treatment are crucial to optimize viral suppression. The differing pharmacokinetic and delivery characteristics of these MOUD offer diverse options. Given the chronic and relapsing nature of both HIV and OUD, long-term approaches are required.

Treatment of opioid dependence with buprenorphine: current update

Opioid maintenance treatment is the first-line approach in opioid dependence. Both the full opioid agonist methadone (MET) and the partial agonist buprenorphine (BUP) are licensed for the treatment of opioid dependence. BUP differs significantly from MET in its pharmacology, side effects, and safety issues. For example, the risk of respiratory depression is lower than with MET. The risk of diversion and injection of BUP have been reduced by also making it available as a tablet containing the opioid antagonist naloxone. This review summarizes the clinical effects of BUP and examines possible factors that can support decisions regarding the use of BUP or MET in opioid-dependent people.

2017 HIVMA of IDSA Clinical Practice Guideline for the Management of Chronic Pain in Patients Living With HIV

Pain has always been an important part of human immunodeficiency virus (HIV) disease and its experience for patients. In this guideline, we review the types of chronic pain commonly seen among persons living with HIV (PLWH) and review the limited evidence base for treatment of chronic noncancer pain in this population. We also review the management of chronic pain in special populations of PLWH, including persons with substance use and mental health disorders. Finally, a general review of possible pharmacokinetic interactions is included to assist the HIV clinician in the treatment of chronic pain in this population.It is important to realize that guidelines cannot always account for individual variation among patients. They are not intended to supplant physician judgment with respect to particular patients or special clinical situations. The Infectious Diseases Society of American considers adherence to these guidelines to be voluntary, with the ultimate determination regarding their application to be made by the physician in the light of each patient's individual circumstances.

Perceived barriers to methadone maintenance treatment among Iranian opioid users

Background

Opioid use is a severe problem in Iran. Despite methadone maintenance treatment (MMT) programs being one of the most important treatment strategies for reducing individual and public harms associated with opioid use, a large proportion of Iranian patients refuse to participate in such treatment programs.

Methods

The present study aims to explore the beliefs and attitudes toward MMT programs of opioid-dependent patients who were participating or had participated in methadone therapy. In-depth interviews were conducted with 23 opioid users between 27 and 58 years of age from Kurdistan provinces.

Results

Overall, six themes were discovered to be key barriers relating to methadone treatment, including financial barriers related to methadone treatment, lack of awareness about methadone treatment, negative attitudes regarding using methadone, worries about methadone’s side effects, social stigma ascribed to methadone therapy, and systemic barriers to methadone treatment.

Conclusion

Our study revealed that the cost of treatment is a major obstacle to attending and continuing at MMT programs and that addicts and their families are not always accurately informed about the duration of MMT programs and the side effects of methadone treatment.

Naltrexone efficacy in treating alcohol-use disorder in individuals with comorbid psychosis: a systematic review

BACKGROUND

Psychotic illnesses, such as schizophrenia, are typically enduring and disabling conditions, impacting individual, family, and societal outcomes. Individuals with these face greater vulnerabilities in developing alcohol-use disorder (AUD). Furthermore, the nature of psychoses, often manifesting with paranoia, cognitive impairment, a lack of insight, sub-optimal treatment adherence, and stigma from others, means that they can pose unique treatment challenges when these two conditions comorbidly occur. These challenges mean that the standard literature on the effectiveness of the opioid antagonist naltrexone in AUD does not necessarily translate to this vulnerable population.

METHODS

Following PRISMA guidelines, we herein systematically reviewed the evidence for naltrexone in individuals with both psychosis and AUD. Overall, there is a paucity of research in this important area, with only nine reports meeting search criteria, only four of which were randomized control trials. Studies compared naltrexone with: placebo, another pharmaceutical agent, or upon changes to baseline drinking behaviour. One study evaluated the long-acting injectable formulation of this drug.

RESULTS

Most studies, including the methodologically more robust ones, supported naltrexone's effectiveness over placebo in terms of reduction in drinking days and numbers of drinks consumed on such days in this cohort. Work comparing naltrexone to other pharmaceutical interventions showed approximate equivalence with disulfiram, and modest superiority over acamprosate.

CONCLUSIONS

On this limited evidence base, this review endorses the use of naltrexone as both safe and effective in those with both psychotic illnesses and AUD. Several key issues remain to be elucidated. Critically, study designs meant that they were limited to individuals with good engagement with services, and levels of adherence were attained that are unlikely to be replicated in this cohort in real-world settings. Finally, effects of specific psychosis symptomatology, not least paranoia and insight, upon naltrexone use, and the reverse directional potential of 'double dysphoria' from an opioid antagonist remain largely unexplored.

Preference for brand-name buprenorphine is related to severity of addiction among outpatients in opioid maintenance treatment

As a form of opioid maintenance treatment, high-dose buprenorphine is increasingly being used in the United States. On the French market since 1996, it is the most commonly prescribed and frequently employed opioid maintenance treatment. For unknown reasons, the brand-name form is used far more often than the generic form (76-24%). The objective was to show that the patients' levels of addiction were differentiated according to the form of buprenorphine currently being used and to their previous experience of a different form. An observational study in 9 sites throughout France used self-assessment questionnaires filled out in retail pharmacies by all patients to whom their prescribed buprenorphine treatment was being delivered. The 151 canvassed pharmacies solicited 879 patients, of whom 724 completed the questionnaires. Participants were statistically similar to non-participants. The patients using the brand-name form subsequent to experience with the generic form exhibited a more elevated addiction severity index and a higher dosage than brand-name form users with no experience of a different form. Compared to generic users, their doses were higher, their was addiction more severe, and their alcohol consumption was more excessive; they were also more likely to make daily use of psychotropic substances. However, the level of misuse or illicit consumption was similar between these groups. Preferring the brand-name buprenorphine form to the generic form is associated with a higher level of severe addiction, a more frequent need for daily psychotropics, and excessive drinking; but the study was unable to show a causal link.

Challenges in managing HIV in people who use drugs

PURPOSE OF REVIEW

HIV management in people who use drugs (PWUD) is typically complex and challenging due to the presence of multiple medical and psychiatric comorbidities as well as social, physical, economic and legal factors that often disrupt the HIV continuum of care. In this review, we describe the individual, health systems and societal barriers to HIV treatment access and care retention for PWUD. In addition, the clinical management of HIV-infected PWUD is often complicated by the presence of multiple infectious and noninfectious comorbidities.

RECENT FINDINGS

Improved HIV treatment outcomes can be enhanced through improved testing and linkage strategies along with better treatment retention and antiretroviral (ART) adherence. Improved ART adherence can be achieved through the provision of opioid substitution therapy (OST), directly administered ART (DAART) and integration of ART with OST services. Recent advances with direct-acting antivirals (DAAs) for hepatitis C virus (HCV) have shown superior outcomes than interferon-based regimes in HIV-HCV coinfected patients. Newer diagnostic technologies for tuberculosis (TB) hold promise for earlier diagnosis for PWUD coinfected with TB, and TB treatment outcomes are improved through combination with OST.

SUMMARY

HIV-infected PWUDs are a key population who frequently experience suboptimal outcomes along the HIV continuum of care. A comprehensive strategy that encompasses evidence-based prevention and treatment interventions that target the individual, family, healthcare system, legal and societal structure is required to ensure greater participation and success in HIV treatment and care.

Treatment readiness, attitudes toward, and experiences with methadone and buprenorphine maintenance therapy among people who inject drugs in Malaysia

BACKGROUND

Little is known about attitudes toward and experiences with opioid maintenance therapy (OMT) among people who inject drugs in Malaysia, a country where people who inject drugs comprise 1.3% of the adult population.

METHODS

In 2010, 460 people who inject drugs in Greater Kuala Lumpur, Malaysia were surveyed to evaluate attitudes toward and experiences with OMT and treatment readiness. Attitudes towards OMT with both methadone and buprenorphine were assessed using an opinions scale. Multivariable linear regression was used to assess correlates of treatment readiness, measured with the 19-item Stages of Change Readiness and Treatment Eagerness Scale (SOCRATES).

RESULTS

All 460 participants used opioids and nearly all (99.1%) met criteria for opioid dependence. Few had had previous experience with methadone (9.3%) or buprenorphine (12.6%) maintenance therapy, yet many had used methadone (55.2%) or buprenorphine (51.7%) outside of treatment settings. Fifteen percent had injected buprenorphine in the past month, and of the few that were currently receiving buprenorphine maintenance therapy, almost all were injecting it. The majority of subjects exhibited a moderate level of treatment readiness and a preference for methadone over buprenorphine. Those with low treatment readiness scores were more likely to have previous experience with compulsory drug detention centers (p<0.01), needle/syringe exchange programs (p<0.005), or be of Indian ethnicity (p<0.001). Past use of methadone (p<0.01), older age (p<0.001), higher stress symptom severity (p<0.001), and sharing of needles or syringes (p<0.05) were associated with higher treatment readiness scores.

CONCLUSION

There are suboptimal levels of OMT experience among people who inject drugs that may be improved by addressing factors that influence patient attitudes. Those individuals with moderate treatment readiness may be targeted by brief motivational and cognitive interventions in primary care, prisons or OMT clinics aimed at improving entry into and retention in treatment.

Benzodiazepine prescribing in children under 15 years of age receiving free medical care on the General Medical Services scheme in Ireland

OBJECTIVE

To examine the prevalence and secular trends in benzodiazepine (BZD) prescribing in the Irish paediatric population. In addition, we examine coprescribing of antiepileptic, antipsychotic, antidepressant and psychostimulants in children receiving BZD drugs and compare BZD prescribing in Ireland to that in other European countries.

SETTING

Data were obtained from the Irish General Medical Services (GMS) scheme pharmacy claims database from the Health Service Executive (HSE)--Primary Care Reimbursement Services (PCRS).

PARTICIPANTS

Children aged 0-15 years, on the HSE-PCRS database between January 2002 and December 2011, were included.

PRIMARY AND SECONDARY OUTCOME MEASURES

Prescribing rates were reported over time (2002-2011) and duration (≤ or >90 days). Age (0-4, 5-11, 12-15) and gender trends were established. Rates of concomitant prescriptions for antiepileptic, antipsychotics, antidepressants and psychostimulants were reported. European prescribing data were retrieved from the literature.

RESULTS

Rates decreased from 2002 (8.56/1000 GMS population: 95% CI 8.20 to 8.92) to 2011 (5.33/1000 GMS population: 95% CI 5.10 to 5.55). Of those children currently receiving a BZD prescription, 6% were prescribed BZD for >90 days. Rates were higher for boys in the 0-4 and 5-11 age ranges, whereas for girls they were higher in the 12-15 age groups. A substantial proportion of children receiving BZD drugs are also prescribed antiepileptic (27%), antidepressant (11%), antipsychotic (5%) and psychostimulant (2%) medicines. Prescribing rates follow a similar pattern to that in other European countries.

CONCLUSIONS

While BZD prescribing trends have decreased in recent years, this study shows that a significant proportion of the GMS children population are being prescribed BZD in the long term. This study highlights the need for guidelines for BZD prescribing in children in terms of clinical indication and responsibility, coprescribing, dosage and duration of treatment.

Medication-assisted treatment of opioid use disorder: review of the evidence and future directions

Medication-assisted treatment of opioid use disorder with physiological dependence at least doubles rates of opioid-abstinence outcomes in randomized, controlled trials comparing psychosocial treatment of opioid use disorder with medication versus with placebo or no medication. This article reviews the current evidence for medication-assisted treatment of opioid use disorder and also presents clinical practice imperatives for preventing opioid overdose and the transmission of infectious disease. The evidence strongly supports the use of agonist therapies to reduce opioid use and to retain patients in treatment, with methadone maintenance remaining the gold standard of care. Combined buprenorphine/naloxone, however, also demonstrates significant efficacy and favorable safety and tolerability in multiple populations, including youth and prescription opioid-dependent individuals, as does buprenorphine monotherapy in pregnant women. The evidence for antagonist therapies is weak. Oral naltrexone demonstrates poor adherence and increased mortality rates, although the early evidence looks more favorable for extended-release naltrexone, which has the advantages that it is not subject to misuse or diversion and that it does not present a risk of overdose on its own. Two perspectives-individualized treatment and population management-are presented for selecting among the three available Food and Drug Administration-approved maintenance therapies for opioid use disorder. The currently unmet challenges in treating opioid use disorder are discussed, as are the directions for future research.

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.

Cytochrome P4503A does not mediate the interaction between methadone and ritonavir-lopinavir

Plasma concentrations of orally administered methadone are reduced by the human immunodeficiency virus protease inhibitor combination ritonavir and lopinavir, but the mechanism is unknown. Methadone metabolism, clearance, and drug interactions have been attributed to CYP3A4, but this remains controversial. This investigation assessed the effects of acute (2 days) and steady-state (2 weeks) ritonavir-lopinavir on intravenous and oral methadone metabolism and clearance, hepatic and intestinal CYP3A4/5 activity (using the probe substrate intravenous and oral alfentanil), and intestinal transporter activity (using oral fexofenadine) in healthy volunteers. Plasma and urine concentrations of methadone and metabolite enantiomers, and other analytes, were determined by mass spectrometry. Acute and chronic ritonavir-lopinavir reduced plasma methadone enantiomer concentrations in half, with an average 2.6- and 1.5-fold induction of systemic and apparent oral methadone clearances. Induction was attributable to stereoselectively increased hepatic methadone N-demethylation, hepatic extraction, and hepatic clearance, and there was a strong correlation between methadone N-demethylation and clearance. Methadone renal clearance was unchanged. Alfentanil's systemic clearance and hepatic extraction, apparent oral clearance, and intestinal extraction were reduced to 25%, 16%, and 35% of control, indicating strong inhibition of hepatic and intestinal CYP3A activities. Ritonavir-lopinavir (acute > chronic) increased fexofenadine exposure, suggesting intestinal P-glycoprotein inhibition. No correlation was found between methadone clearance and CYP3A activity. Acute and steady-state ritonavir-lopinavir stereoselectively induced methadone N-demethylation and clearance, despite significant inhibition of hepatic and intestinal CYP3A activity. Ritonavir-lopinavir inhibited intestinal transporters activity but had no effect on methadone bioavailability. These results do not support a significant role for CYP3A or ritonavir-lopinavir-inhibitable intestinal transporters in single-dose methadone disposition.

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.

Adherence to HIV treatment and care among previously homeless jail detainees

HIV-infected persons entering the criminal justice system (CJS) often experience suboptimal healthcare system engagement and social instability, including homelessness. We evaluated surveys from a multisite study of 743 HIV-infected jail detainees prescribed or eligible for antiretroviral therapy (ART) to understand correlates of healthcare engagement prior to incarceration, focusing on differences by housing status. Dependent variables of healthcare engagement were: (1) having an HIV provider, (2) taking ART, and (3) being adherent (≥95% of prescribed doses) to ART during the week before incarceration. Homeless subjects, compared to their housed counterparts, were significantly less likely to be engaged in healthcare using any measure. Despite Ryan White funding availability, insurance coverage remains insufficient among those entering jails, and having health insurance was the most significant factor correlated with having an HIV provider and taking ART. Individuals interfacing with the CJS, especially those unstably housed, need innovative interventions to facilitate healthcare access and retention.

High-sensitivity analysis of buprenorphine, norbuprenorphine, buprenorphine glucuronide, and norbuprenorphine glucuronide in plasma and urine by liquid chromatography-mass spectrometry

A new method using ultra-fast liquid chromatography and tandem mass spectrometry (UFLC-MS/MS) was developed for the simultaneous determination of buprenorphine and the metabolites norbuprenorphine, buprenorphine-3β-glucuronide, and norbuprenorphine-3β-glucuronide in plasma and urine. Sample handling, sample preparation and solid-phase extraction procedures were optimized for maximum analyte recovery. All four analytes of interest were quantified by positive ion electrospray ionization tandem mass spectrometry after solid-phase microextraction. The lower limits of quantification in plasma were 1pg/mL for buprenorphine and buprenorphine glucuronide, and 10pg/mL for norbuprenorphine and norbuprenorphine glucuronide. The lower limits of quantitation in urine were 10pg/mL for buprenorphine, norbuprenorphine and their glucuronides. Overall extraction recoveries ranged from 68-100% in both matrices. Interassay precision and accuracy was within 10% for all four analytes in plasma and within 15% in urine. The method was applicable to pharmacokinetic studies of low-dose buprenorphine.

Mechanism of autoinduction of methadone N-demethylation in human hepatocytes

BACKGROUND

There is considerable interindividual and intraindividual variability in methadone metabolism and clearance. Methadone dosing is particularly challenging during initiation of therapy, because of time-dependent increases in hepatic clearance (autoinduction). Although methadone N-demethylation is catalyzed in vitro by cytochrome P4502B6 (CYP2B6) and CYP3A4, and clearance in vivo depends on CYP2B6, mechanism(s) of autoinduction are incompletely understood. In this investigation, we determined mechanism(s) of methadone autoinduction using human hepatocytes.

METHODS

Fresh human hepatocytes were exposed to 0.1 to 10 µM methadone for 72 hours. Cells were washed and methadone N-demethylation assessed. CYP2B6, CYP3A4, and CYP3A5 messenger RNA (mRNA), protein expression (by gel-free high-performance liquid chromatography mass spectrometry) and catalytic activity (bupropion hydroxylation and alfentanil dealkylation for CYP2B6 and CYP3A4/5, respectively) were measured. Mechanisms of CYP induction were characterized using pregnane X receptor and constitutive androstane receptor reporter gene assays.

RESULTS

Methadone (10 µM) increased methadone N-demethylation 2-fold, CYP2B6 and CYP3A4 mRNA 3-fold, and protein expression 2-fold. CYP3A5 mRNA was unchanged. CYP2B6 and CYP3A4/5 activities increased 2-fold. Induction by methadone enantiomers (R-methadone versus S-methadone) did not differ. Induction was relatively weak compared with maximum induction by phenobarbital and rifampin. Lower methadone concentrations had smaller effects. Methadone was an agonist for the pregnane X receptor but not the constitutive androstane receptor.

CONCLUSIONS

Methadone caused concentration-dependent autoinduction of methadone N-demethylation in human hepatocytes, related to induction of CYP2B6 and CYP3A4 mRNA expression, protein expression, and catalytic activity. Induction was related to pregnane X receptor but not constitutive androstane receptor activation. These in vitro findings provide mechanistic insights into clinical autoinduction of methadone metabolism and clearance.

Role of cytochrome P4502B6 in methadone metabolism and clearance

Methadone N-demethylation in vitro is catalyzed by hepatic cytochrome P4502B6 (CYP2B6) and CYP3A4, but clinical disposition is often attributed to CYP3A4. This investigation tested the hypothesis that CYP2B6 is a prominent CYP isoform responsible for clinical methadone N-demethylation and clearance, using the in vivo mechanism-based CYP2B6 inhibitor ticlopidine, given orally for 4 days. A preliminary clinical investigation with the CYP3A4/5 substrate probe alfentanil established that ticlopidine did not inhibit intestinal or hepatic CYP3A4/5. Subjects received intravenous plus oral (deuterium-labeled) racemic methadone before and after ticlopidine. Ticlopidine significantly and stereoselectively (S > R) inhibited methadone N-demethylation, decreasing plasma metabolite/methadone area under the curve ratios and metabolite formation clearances. Ticlopidine also significantly increased the dose-adjusted plasma area under the curve for R- and S-methadone by 20% and 60%, respectively, after both intravenous and oral dosing. CYP2B6 inhibition reduces methadone N-demethylation and clearance, and alters methadone concentrations, demonstrating an important role for CYP2B6 in clinical methadone disposition.

Mechanism of efavirenz influence on methadone pharmacokinetics and pharmacodynamics

Mechanisms by which efavirenz diminishes methadone plasma concentrations are unknown. This investigation determined efavirenz influence on clinical methadone disposition and miosis, intravenous and oral alfentanil clearance (hepatic and intestinal cytochrome P450 3A4/5 (CYP3A4/5) activity), fexofenadine disposition (intestinal transporters activity), and efavirenz clearance and 8-hydroxylation (CYP2B6 activity), and human hepatocyte effects. Efavirenz induced systemic and oral alfentanil clearances two- to fivefold and induced efavirenz 8-hydroxylation. Efavirenz stereoselectively decreased methadone plasma concentrations 50-70%. Methadone systemic and oral clearances, hepatic clearance and extraction ratio, N-demethylation, and metabolite formation clearance were stereoselectively increased two- to threefold. Bioavailability decreased. Efavirenz shifted methadone concentration-miosis curves leftward and upward. Efavirenz induced hepatocyte CYP2B6 and CYP3A4 expression, activity, and methadone N-demethylation. Results show that efavirenz coinduced hepatic CYP2B6 and CYP3A4/5, coinduced hepatic and intestinal CYP3A4/5, and coinduced gastrointestinal CYP3A4/5 and efflux transporters. Methadone disposition was most consistent with efavirenz induction of hepatic CYP2B6-mediated methadone N-demethylation. Efavirenz may alter methadone pharmacodynamics.

Lack of indinavir effects on methadone disposition despite inhibition of hepatic and intestinal cytochrome P4503A (CYP3A)

BACKGROUND

Methadone disposition and pharmacodynamics are highly susceptible to interactions with antiretroviral drugs. Methadone clearance and drug interactions have been attributed to cytochrome P4503A4 (CYP3A4), but actual mechanisms are unknown. Drug interactions can be clinically and mechanistically informative. This investigation assessed effects of the protease inhibitor indinavir on methadone pharmacokinetics and pharmacodynamics, hepatic and intestinal CYP3A4/5 activity (using alfentanil), and intestinal transporter activity (using fexofenadine).

METHODS

Twelve healthy volunteers underwent a sequential crossover. On three consecutive days they received oral alfentanil plus fexofenadine, intravenous alfentanil, and intravenous plus oral (deuterium-labeled) methadone. This was repeated after 2 weeks of indinavir. Plasma and urine analytes were measured by mass spectrometry. Opioid effects were measured by miosis.

RESULTS

Indinavir significantly inhibited hepatic and first-pass CYP3A activity. Intravenous alfentanil systemic clearance and hepatic extraction were reduced to 40-50% of control, apparent oral clearance to 30% of control, and intestinal extraction decreased by half, indicating 50% and 70% inhibition of hepatic and first-pass CYP3A activity. Indinavir increased fexofenadine area under the plasma concentration-time curve 3-fold, suggesting significant P-glycoprotein inhibition. Indinavir had no significant effects on methadone plasma concentrations, methadone N-demethylation, systemic or apparent oral clearance, renal clearance, hepatic extraction or clearance, or bioavailability. Methadone plasma concentration-effect relationships were unaffected by indinavir.

CONCLUSIONS

Despite significant inhibition of hepatic and intestinal CYP3A activity, indinavir had no effect on methadone N-demethylation and clearance, suggesting little or no role for CYP3A in clinical disposition of single-dose methadone. Inhibition of gastrointestinal transporter activity had no influence of methadone bioavailability.

Pharmacological enhancement of naltrexone treatment for opioid dependence: a review

PURPOSE: Opioid dependence (OD) is a serious and growing clinical condition with increasing social costs that requires expanding treatment beyond opioid agonist substitution. The opioid antagonist naltrexone has displayed a remarkable association of theoretical effectiveness and poor clinical utility in treating OD due to noncompliant behavior and low acceptability among patients, only partly modified by psychosocial interventions. We reviewed pharmacological studies, including naltrexone depot formulations and combination treatments. METHOD: We searched PubMed for clinical studies on the use of naltrexone implants and slow-release injections in OD, and investigations using adjunct medications to improve naltrexone maintenance therapy of OD. We discussed the results in view of their application to the clinical practice. RESULTS: Significant reduction in opioid use and improved retention in treatment have been found in several studies using depot naltrexone formulations, some of which are controlled clinical trials. Pilot investigations have gathered initial positive results on the use of naltrexone in combination with serotonin reuptake inhibitors, α-2 adrenergic, opioid, and γ-aminobutyric acid agonist medications. CONCLUSION: Current evidence suggests that more research on effectiveness and safety is needed in support of depot naltrexone treatment for OD. Further research comparing slow-release with oral naltrexone and opioid agonist medications will help characterize the role of opioid antagonist-mediated treatment of OD. Preliminary investigations on naltrexone combination treatments suggest the opportunity to continue study of new mixed receptor activities for the treatment of OD and other drug addictions.