Absence of opioid withdrawal symptoms in patients receiving methadone and the protease inhibitor lopinavir-ritonavir

Drug-drug interactions and clinical considerations with co-administration of antiretrovirals and psychotropic drugs

Psychotropic medications are frequently co-prescribed with antiretroviral therapy (ART), owing to a high prevalence of psychiatric illness within the population living with HIV, as well as a 7-fold increased risk of HIV infection among patients with psychiatric illness. While ART has been notoriously associated with a multitude of pharmacokinetic drug interactions involving the cytochrome P450 enzyme system, the magnitude and clinical impact of these interactions with psychotropics may range from negligible effects on plasma concentrations to life-threatening torsades de pointes or respiratory depression. This comprehensive review summarizes the currently available information regarding drug-drug interactions between antiretrovirals and pharmacologic agents utilized in the treatment of psychiatric disorders-antidepressants, stimulants, antipsychotics, anxiolytics, mood stabilizers, and treatments for opioid use disorder and alcohol use disorder-and provides recommendations for their management. Additionally, overlapping toxicities between antiretrovirals and the psychotropic classes are highlighted. Knowledge of the interaction and adverse effect potential of specific antiretrovirals and psychotropics will allow clinicians to make informed prescribing decisions to better promote the health and wellness of this high-risk population.

Methadone Metabolism and Drug-Drug Interactions: In Vitro and In Vivo Literature Review

Methadone is utilized for the treatment of individuals with opiate dependence. Methadone undergoes N-demethylation by multiple cytochrome P450 (CYP) enzymes including CYP3A4, CYP2B6, CYP2C19, CYP2D6, CYP2C9, and CYP2C8. In vivo, polymorphism effects on methadone systemic exposure have been noted for CYP2B6, CYP3A4, and CYP2D6. Clinical drug interaction studies with antiviral drugs in methadone maintenance treatment patients yield varying results on methadone pharmacokinetics and pharmacodynamics. In general, CYP inhibitors altered methadone exposure with no adverse effects. CYP inducers generally decreased methadone exposure with some reports of withdrawal symptoms in the subjects. Interaction studies with antiviral drug combinations yielding differing results depend on the enzyme(s) affected. For certain antiviral medicines which are dual inhibitor(s) and inducer(s) for CYP enzymes, their effect on methadone pharmacokinetics can change with time since the effect of induction is usually delayed compared to the effect of inhibition.

Finding what works: identification of implementation strategies for the integration of methadone maintenance therapy and HIV services in Vietnam

Background

Integration of methadone maintenance therapy (MMT) and HIV services is an evidence-based intervention (EBI) that benefits HIV care and reduces costs. While MMT/HIV integration is recommended by the World Health Organization and the Centers for Disease Control and Prevention, it is not widely implemented, due to organizational and operational barriers. Our study applied an innovative process to identify implementation strategies to address these barriers.

Methods

Our process was adapted from the Expert Recommendations for Implementing Change (ERIC) protocol and consisted of two main phases. In Phase 1, we conducted 16 in-depth interviews with stakeholders and developed matrices to display barriers to integration. In Phase 2, we selected implementation strategies that addressed the barriers identified in Phase 1 and conducted a poll to vote on the most important and feasible strategies among a panel with expertise in cultural context and implementation science.

Results

Barriers fell into two broad categories: policy and programmatic. At the policy level, barriers included lack of a national mandate, different structures (MMT vs. HIV clinic) for cost reimbursement and staff salaries, and resistance on the part of staff to take on additional tasks without compensation. Programmatic barriers included the need for cross-training in MMT and HIV tasks, staff accountability, and commitment from local leaders. In Phase 2, we focused on programmatic challenges. Based on voting results and iterative dialogue with our expert panel, we selected several implementation strategies in the domains of technical assistance, staff accountability, and local commitment that targeted these barriers.

Conclusions

Key programmatic barriers to MMT/HIV integration in Vietnam may be addressed through implementation strategies that focus on technical assistance, staff accountability, and local commitment. Our process of identifying implementation strategies was simple, low cost, and potentially replicable to other settings.

Electronic supplementary material

The online version of this article (doi:10.1186/s13012-016-0420-8) contains supplementary material, which is available to authorized users.

A Review of the Toxicity of HIV Medications II: Interactions with Drugs and Complementary and Alternative Medicine Products

For many patients today, HIV has become a chronic disease. For those patients who have access to and adhere to lifelong antiretroviral (ARV) therapy, the potential for drug-drug interactions has become a real and life-threatening concern. It is known that most ARV drug interactions occur through the cytochrome P450 (CYP) pathway. Medications for comorbid medical conditions, holistic supplements, and illicit drugs can be affected by CYP inhibitors and inducers and have the potential to cause harm and toxicity. Protease inhibitors (PIs) tend to inhibit CYP3A4, while most non-nucleoside reverse transcriptase inhibitors (NNRTIs) tend to induce the enzyme. As such, failure to adjust the dose of co-administered medications, such as statins and steroids, may lead to serious complications including rhabdomyolysis and hypercortisolism, respectively. Similarly, gastric acid blockers can decrease several ARV absorption, and warfarin doses may need to be adjusted to maintain therapeutic concentrations. Illicit drugs such as methylenedioxymethamphetamine (MDMA, "ecstasy") in combination with PIs lead to increased toxicity, while the concomitant administration of sedative drugs such as midazolam and alprazolam in patients taking PIs can result in prolonged sedation, delayed recovery, and increased length of stay. Even supplements like St. John's Wort can alter PI concentrations. In theory, any drug that is metabolized by CYP has potential for a pharmacokinetic drug-drug interaction with all PIs, cobicistat, and most NNRTIs. When adding a new medication to an ARV regimen, use of a drug-drug interaction software and/or consultation with a clinical pharmacist/pharmacologist or HIV specialist is recommended.

Drug-Drug Interactions With Antiviral Agents in People Who Inject Drugs Requiring Substitution Therapy

OBJECTIVE

To describe potential drug-drug interactions in the area of HIV/hepatitis C virus (HCV) coinfection and injection drug use, including those between antiretrovirals (ARVs), direct-acting antivirals (DAAs), and opioid-agonist therapy, and to supply a practical approach to their management.

DATA SOURCES

We searched PubMed for relevant articles published up until February 2015 as well as conference reports and drug-drug-interaction Web sites.

DATA SELECTION AND DATA EXTRACTION

We used the following search terms: pharmacokinetic and pharmacodynamic drug-drug interaction, opioid substitution, HIV, hepatitis and the individual names of the relevant agents of the following drug classes and the drug classes itself: reverse transcriptase inhibitors, nonnucleoside reverse transcriptase inhibitors, protease inhibitors, direct-acting antivirals, opioide, benzodiazepines, anticonvulsants, antidepressants and antipsychotics. Additional references were identified from a review of literature citations and drug-drug interaction Web sites. In our evaluation, we included German- and English-language studies and reports addressing drug-drug interactions between opioid agonist therapy and ARVs or DAAs.

DATA SYNTHESIS

Pharmacokinetic data were available for all ARVs and DAAs except rilpivirine, indinavir, saquinavir, maraviroc, dolutegravir, and MK-8742 with buprenorphine as well as maraviroc with methadone Drug-drug interactions of potential clinical relevance are most likely to occur between opioid-replacement therapy and ARVs, particularly the nonnucleoside reverse transcriptase inhibitors, efavirenz and nevirapine, and HIV protease inhibitors.

CONCLUSION

Integrase inhibitors may be safely coadministered with opioid-replacement therapy. With respect to HCV DAAs, most currently approved and late-stage investigational agents do not have clinically significant interactions with opioid-replacement therapy. ARV and DAAs may interact with other drug classes commonly used in the opioid-dependent population, including benzodiazepines, antidepressants, anticonvulsants, and antipsychotics.

The role of lopinavir/ritonavir (Kaletra®) in the management of HIV infected adults

As the HIV pandemic enters its third decade, more sophisticated and efficacious therapies are continually being developed. This article provides an in-depth review of the first coformulated boosted protease inhibitor available on the world market, lopinavir/ritonavir (Kaletra). Included in this review is an overview of the current market place, the chemistry, pharmacokinetics, clinical efficacy and side-effect profile of lopinavir/ritonavir. In addition, an expert opinion and commentary on the clinical applications of this drug is provided.

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.

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.

Polypharmacy in the HIV-infected older adult population

The prevalence of human immunodeficiency virus (HIV) infection among people older than 50 years is increasing. Older HIV-infected patients are particularly at risk for polypharmacy because they often have multiple comorbidities that require pharmacotherapy. Overall, there is not much known with respect to both the impact of aging on medication use in HIV-infected individuals, and the potential for interactions with highly active antiretroviral therapy (HAART) and coadministered medications and its clinical consequences. In this review, we aim to provide an overview of polypharmacy with a focus on its impact on the HIV-infected older adult population and to also provide some clinical considerations in this high-risk population.

Methadone: a review of drug-drug and pathophysiological interactions

Numerous established and potential drug interactions with methadone are clinically important in people treated with methadone either for addiction or for chronic pain. Methadone users often have comorbidities and are prescribed drugs that may interact with methadone. Methadone is extensively metabolized by cytochrome P450 (CYP) 3A4 and to a lesser extent by CYP 1A2, 2D6, 2D8, 2C9/2C8, 2C19, and 2B6. Eighty-six percent of methadone is protein bound, predominately to α1-acid glycoprotein (AGP). Polymorphisms in or interactions with CYPs that metabolize methadone, changes in protein binding, and other pathophysiological conditions affect the pharmacokinetic properties of methadone. It is critical for health care providers who treat patients on methadone to have adequate information on the interactions of methadone with other drugs of abuse and other medications. We set out to describe drug-drug interactions as well as physiological and pathophysiological factors that may impact the pharmacokinetics of methadone. Using MEDLINE, we conducted a systematic search for papers and related abstracts published between 1966 and June 2010. Keywords that included methadone, drug-drug interactions, CYP P450 and AGP identified a total of 7709 papers. Other databases, including the Cochrane Database of Systematic Reviews and Scopus, were also searched; an additional 929 papers were found. Final selection of 286 publications was based on the relevance of each paper to the topic. Over 50 such interactions were found. Interactions of methadone with other drugs can lead to increased or decreased methadone drug levels in patients and result in potential overdose or withdrawal, respectively. The former can contribute to methadone's fatality. Prescribers of methadone and pharmacists should enquire about any new medications (including natural products and over-the-counter medications) periodically, and especially when an otherwise stable patient suddenly experiences drug craving, withdrawal or intoxication.

Strategies to improve access to and utilization of health care services and adherence to antiretroviral therapy among HIV-infected drug users

We review five innovative strategies to improve access, utilization, and adherence for HIV-infected drug users and suggest areas that need further attention. In addition, we highlight two innovative programs. The first increases access and utilization through integrated HIV and opioid addiction treatment with buprenorphine in a community health center, and the second incorporates adherence counseling for antiretroviral therapy in methadone programs. Preliminary evaluations demonstrated that these strategies may improve both HIV and opioid addiction outcomes and may be appropriate for wider dissemination. Further refinement and expansion of strategies to improve outcomes of HIV-infected drug users is warranted.

Dose-related reduction in bupropion plasma concentrations by ritonavir

The effect of repeat oral doses of ritonavir, at high (600 mg twice daily) and low (100 mg twice daily) doses, on the pharmacokinetics of a single dose of bupropion was evaluated in healthy volunteers. Subjects received a single dose of 150 mg of bupropion on day 1 and twice-daily ritonavir from day 8 through day 30. Ritonavir was up-titrated from 300 mg twice daily to 600 mg twice daily in the high-dose ritonavir study, whereas subjects remained on 100 mg twice-daily ritonavir in low-dose ritonavir study. Subjects received a second single dose of bupropion on day 24. Serial blood samples were obtained to evaluate the pharmacokinetics of bupropion and its metabolites on days 1 and 24. Steady-state ritonavir led to a decrease of area under the curve and maximum plasma concentration of bupropion by 62% to 67% in the high-dose study and by 21% to 22% in the low-dose study, indicating a drug interaction of statistical and clinical significance, particularly at high doses of ritonavir. These studies demonstrate that the reduction of bupropion exposure by ritonavir is dose-related. Dosage adjustment of bupropion may be needed when administered with ritonavir. However, the maximum recommended daily dose of bupropion should not be exceeded.

Mechanism of ritonavir changes in methadone pharmacokinetics and pharmacodynamics: I. Evidence against CYP3A mediation of methadone clearance

Ritonavir diminishes methadone plasma concentrations, an effect attributed to CYP3A induction, but the actual mechanisms are unknown. We determined ritonavir effects on stereoselective methadone pharmacokinetics and clinical effects (pupillary miosis) in healthy human immunodeficiency virus-negative volunteers. Subjects received intravenous plus oral (deuterium-labeled) racemic methadone after no ritonavir, short-term (3-day) ritonavir, and steady-state ritonavir. Acute and steady-state ritonavir, respectively, caused 1.5- and 2-fold induction of systemic and apparent oral R- and S-methadone clearances. Ritonavir increased renal clearance 40-50%, and stereoselectively (S > R) increased hepatic methadone N-demethylation 50-80%, extraction twofold, and clearance twofold. Bioavailability was unchanged despite significant inhibition of intestinal P-glycoprotein. Intestinal and hepatic CYP3A was inhibited > 70%. Ritonavir shifted methadone plasma concentration-miosis curves leftward and upward. Rapid ritonavir induction of methadone clearance results from increased renal clearance and induced hepatic metabolism. Induction of methadone metabolism occurred despite profound CYP3A inhibition, suggesting no role for CYP3A in clinical methadone metabolism and clearance. Ritonavir may alter methadone pharmacodynamics.

Methadone pharmacokinetics are independent of cytochrome P4503A (CYP3A) activity and gastrointestinal drug transport: insights from methadone interactions with ritonavir/indinavir

BACKGROUND

Methadone clearance is highly variable, and drug interactions are problematic. Both have been attributed to CYP3A, but actual mechanisms are unknown. Drug interactions can provide such mechanistic information. Ritonavir/indinavir, one of the earliest protease inhibitor combinations, may inhibit CYP3A. We assessed ritonavir/indinavir effects on methadone pharmacokinetics and pharmacodynamics, intestinal and hepatic CYP3A activity, and intestinal transporters (P-glycoprotein) activity. CYP3A and transporters were assessed with alfentanil and fexofenadine, respectively.

METHODS

Twelve healthy human immunodeficiency virus-negative volunteers underwent a sequential three-part crossover. On three consecutive days, they received oral alfentanil/fexofenadine, intravenous alfentanil, and intravenous plus oral (deuterium-labeled) methadone, repeated after acute (3 days) and steady-state (2 weeks) ritonavir/indinavir. Plasma and urine analytes were measured by mass spectrometry. Opioid effects were assessed by miosis.

RESULTS

Alfentanil apparent oral clearance was inhibited more than 97% by both acute and steady-state ritonavir/indinavir, and systemic clearance was inhibited more than 90% due to diminished hepatic and intestinal extraction. Ritonavir/indinavir increased fexofenadine area under the plasma concentration-time curve four- to five-fold, suggesting significant inhibition of gastrointestinal P-glycoprotein. Ritonavir/indinavir slightly increased methadone N-demethylation, but it had no significant effects on methadone plasma concentrations or on systemic or apparent oral clearance, renal clearance, hepatic extraction or clearance, or bioavailability. Ritonavir/indinavir had no significant effects on methadone plasma concentration-effect relationships.

CONCLUSIONS

Inhibition of both hepatic and intestinal CYP3A activity is responsible for ritonavir/indinavir drug interactions. Methadone disposition was unchanged, despite profound inhibition of CYP3A activity, suggesting little or no role for CYP3A in clinical methadone metabolism and clearance. Methadone bioavailability was unchanged, despite inhibition of gastrointestinal P-glycoprotein activity, suggesting that this transporter does not limit methadone intestinal absorption.

Co-infections and co-therapies: treatment of HIV in the presence of hepatitis C and hepatitis B

An increasing number of people are chronically infected with HIV and HCV, and/or HBV owing to shared routes of transmission. With the advent of HAART, liver disease secondary to hepatitis co-infections has emerged as a leading cause of morbidity and mortality in HIV-infected persons. There is increasing need to manage dual infection, but treatment is complicated by co-morbidities, overlapping toxicities, drug activities and resistance. A model of treatment that builds on the lessons learned from the treatment of HIV has evolved to maximize success of treating dual infections. This review will address current strategies for the management of HIV in the setting of HCV and HBV co-infection and discuss future treatment directions and challenges.

Induction effects of ritonavir: implications for drug interactions

OBJECTIVE

To review the literature on the induction effects of ritonavir on the cytochrome P450 enzyme system and glucuronyl transferase and identify resultant established and potential drug interactions.

DATA SOURCES

Primary literature was identified from MEDLINE (1950-April 2008), EMBASE (1988-April 2008) and International Pharmaceutical Abstracts (1970-April 2008) using the search terms ritonavir, cytochrome P450 enzyme system, enzyme induction, glucuronyl transferase, and drug interactions. Additionally, relevant conference abstracts and references of relevant articles were reviewed.

STUDY SELECTION AND DATA ABSTRACTION

All English-language articles and abstracts identified were reviewed.

DATA SYNTHESIS

Ritonavir is a well-known inhibitor of the metabolism of numerous medications that are substrates of the CYP3A and CYP2D6 pathways. It also exhibits a biphasic, time-dependent effect on P-glycoprotein of inhibition followed by induction. Numerous pharmacokinetic studies suggested that ritonavir induces cytochrome P450 enzymes 3A, 1A2, 2B6, 2C9, and 2C19, as well as glucuronyl transferase. Additionally, several case reports described clinically significant subtherapeutic effects of drugs metabolized by these isoenzymes when coadministered with ritonavir. Both therapeutic and boosting doses of ritonavir appear to induce these enzymes; however, most of the studies of low-dose ritonavir involved a second protease inhibitor such as lopinavir, darunavir, or tipranavir. It is, therefore, difficult to distinguish the relative effects of additional medications unless well-designed, 3-way studies are conducted.

CONCLUSIONS

At both therapeutic and boosting doses, ritonavir exhibits a clinically relevant induction effect on numerous drug-metabolizing enzymes. A decrease or loss of therapeutic effect may be observed when ritonavir is coadministered with medications that are substrates for these enzymes. It is important for clinicians to be aware of drugs potentially impacted by ritonavir therapy to identify and manage these interactions.

Actual and potential drug interactions associated with methadone

OBJECTIVE

To identify and characterize methadone-related drug interactions, as well as factors accounting for the variability in manifesting these interactions clinically.

DESIGN

Systematic review of the primary literature.

METHODS

Over 200 articles, reports of clinical trials, and case reports were reviewed. Studies and case reports were included if they revealed either quantitative or qualitative methods to identify, evaluate severity of, or compare methadone-related drug interactions.

RESULTS OF DATA SYNTHESIS

The evidence base associated with methadone drug interactions is underdeveloped in general, as the majority of references found were case reports or case series. Most of the studies and reports focused on inpatients receiving methadone maintenance treatment (MMT) that were between 20 and 60 years of age, taking 200 mg/day of methadone or less. Evidence supporting the involvement of lesser known cytochrome P450 enzymes such as 2B6 is emerging, which may partially explain the inconsistencies previously found in studies looking specifically at 3A4 in vitro and in vivo. Genetic variability may play a role in the pharmacokinetics and pharmacodynamics of many medications, including methadone.

CONCLUSIONS

Drug interactions associated with methadone and their clinical significance are still poorly understood in general. Many tertiary drug information references and review articles report interactions associated with methadone in a general sense, much of which is theoretical and not verified by case reports, much less well-designed clinical trials. The majority of drug interaction reports that do exist were performed in the MMT population, which may differ significantly from chronic pain or cancer pain populations.

Methadone dosing strategies in HIV-infected injection drug users enrolled in a directly observed therapy program

OBJECTIVES

We have measured methadone dose adjustments and treatment responses after nevirapine (NVP)-, efavirenz (EFV)-, ritonavir-boosted lopinavir (LPV/r), or atazanavir (ATV; with or without ritonavir)-based highly active antiretroviral therapy (HAART) was initiated in injection drug users (IDUs).

METHODS

We identified 120 IDUs receiving HAART and methadone within a directly observed therapy (DOT) program. Follow-up was according to clinical standards, with changes in methadone dose being made as required to achieve clinical stabilization within the first 3 months of HAART.

RESULTS

The observed median methadone dose changes from baseline were 20 mg/d (P<0.001) in patients on NVP, with 32 (86%) of 37 patients requiring daily dose increases, and 7.5 mg/d (P=0.004) in patients on EFV, with 11 (61%) of 18 patients requiring daily dose increases. Conversely, median changes were 0 mg/d for patients on LPV/r (P=0.56) or ATV (P=0.95). Virologic suppression (HIV RNA<400 copies/mL) was achieved in 26 (70%) of 37, 12 (67%) of 18, 25 (76%) of 33, and 24 (75%) of 32 patients receiving NVP-, EFV-, LPV/r-, and ATV-based regimens, respectively (P=0.89).

CONCLUSIONS

Although methadone-based DOT can be a successful tool for the coadministration of HAART, careful monitoring is required to ensure that methadone withdrawal does not adversely affect the goals of treatment, particularly when nonnucleoside reverse transcriptase inhibitors are used.

Treatment of opioid dependence and coinfection with HIV and hepatitis C virus in opioid-dependent patients: the importance of drug interactions between opioids and antiretroviral agents

The occurrence of human immunodeficiency virus (HIV) disease and hepatitis C is common in injection drug users, most of whom are opioid dependent. Methadone pharmacotherapy has been the most widely used treatment for opioid addiction in this population. Methadone has significant, adverse drug-drug interactions with many antiretroviral therapeutic agents that can contribute to nonadherence and poor clinical outcomes in this high-risk population. The present article summarizes current knowledge about interactions between methadone and antiretroviral medications. Buprenorphine is the newest agent available for the treatment of opioid dependence and may have fewer adverse interactions with antiretroviral agents. Buprenorphine has a significant pharmacokinetic interaction with efavirenz but no pharmacodynamic interaction; therefore, simultaneous administration of these drugs is not associated with opioid withdrawal, as has been observed with methadone. This promising finding may simplify the treatment of opioid-dependent patients with HIV disease and should also improve clinical outcomes for persons coinfected with HIV and hepatitis C virus.

Lopinavir/ritonavir reduces bupropion plasma concentrations in healthy subjects

Limited data are available about the effect of steady-state lopinavir and ritonavir (LPV/r) on bupropion pharmacokinetics. As patients may benefit by using these two agents in combination, this study determined the extent and direction of this drug-drug interaction. Twelve healthy volunteers received a single 100 mg dose of sustained-release bupropion before and after 2 weeks of treatment with LPV/r 400 mg/100 mg twice daily. Pharmacokinetics profiles were determined on days 1 and 30 for bupropion and hydroxybupropion and days 29 and 30 for LPV/r. LPV/r administration significantly decreased bupropion maximum plasma concentration (C(max)) by 57% (90% confidence interval (CI), 38-76%; P<0.01) and area under the curve (AUC) infinity by 57% (90% CI, 32-83%; P<0.01). Hydroxybupropion C(max) and AUC infinity decreased by 31% (90% CI, 7-55%; P<0.01) and by 50% (90% CI, 34-65%; P<0.01), respectively. No significant changes in the pharmacokinetics of LPV/r were found following administration of a single dose of bupropion. Concurrent use of LPV/r and bupropion resulted in decreased exposure to bupropion and its active metabolite hydroxybupropion that may necessitate as much as a 100% dose increase of bupropion. A probable mechanism for this interaction is the concurrent induction of cytochrome P450 2B6 and UDP-glucuronosyltransferase enzymes. LPV/r exposure is unaffected by a single dose of bupropion.

Pharmacokinetic interactions between HIV antiretroviral therapy and drugs used to treat opioid dependence

Injection drug use is a common risk factor for HIV infection, and opioid use and dependence is the underlying condition that often fuels HIV risk behaviour and subsequent HIV seroconversion among injection drug users (IDUs). Treatment of opioid dependence often requires continued opioid administration in the form of substitution therapy, which means that opioid-using IDUs often continue receiving opioids even after cessation of illicit drug use. The concurrent use of both antiretrovirals and opioids in HIV-positive individuals is thus common. This review was undertaken to summarise current knowledge on the interactions between the opioids and antiretrovirals and to make recommendations on the treatment of HIV-positive opioid-dependent patients.

Lopinavir/ritonavir induces the hepatic activity of cytochrome P450 enzymes CYP2C9, CYP2C19, and CYP1A2 but inhibits the hepatic and intestinal activity of CYP3A as measured by a phenotyping drug cocktail in healthy volunteers

OBJECTIVE

The effect of lopinavir/ritonavir (LPV/r) administration on cytochrome P450 (CYP) enzyme activity was quantified using a phenotyping biomarker cocktail. Changes in CYP2C9, CYP2C19, CYP3A, CYP1A2, N-acetyltransferase-2 (NAT-2), and xanthine oxidase (XO) activities were evaluated using warfarin (WARF) + vitamin K, omeprazole (OMP), intravenous (IV) and oral (PO) midazolam (MDZ), and caffeine (CAF).

DESIGN

: Open-label, multiple-dose, pharmacokinetic study in healthy volunteers.

METHODS

Subjects (n = 14) simultaneously received PO WARF 10 mg, vitamin K 10 mg, OMP 40 mg, CAF 2 mg/kg, and IV MDZ 0.025 mg/kg on days (D) 1 and 14, and PO MDZ 5 mg on D2 and D15. LPV/r (400/100 mg twice daily) was administered on D4-17. CYP2C9 and CYP2C19 activities were quantified by S-WARF AUC0-inf and OMP/5-hydroxy OMP ratio, respectively. CYP1A2, NAT-2, and XO activities were quantified by urinary CAF metabolite ratios. Hepatic and intestinal + hepatic CYP3A activities were quantified by IV (CL) and PO (CL/F) MDZ clearance, respectively.

RESULTS

After LPV/r therapy, CYP2C9, CYP2C19, and CYP1A2 activity increased by 29%, 100%, and 43% (P = 0.001, 0.046, and 0.001), respectively. No changes were seen in NAT-2 or XO activity. Hepatic and intestinal + hepatic CYP3A activity decreased by 77% (P < 0.001) and 92% (P = 0.001), respectively.

CONCLUSION

LPV/r therapy results in modest induction of CYP1A2 and CYP2C9 and potent induction of CYP2C19 activity. Increasing doses of concomitant medications metabolized by these enzymes may be necessary. LPV/r inhibited intestinal CYP3A to a greater extent than hepatic CYP3A activity. Doses of concomitant CYP3A substrates should be reduced when combined with LPV/r, although intravenously administered compounds may require less of a relative dose reduction than orally administered compounds.

Interacciones clínicas y farmacocinéticas entre metadona y nelfinavir (estudio Nemesia)

BACKGROUND AND OBJECTIVE

Patients on methadone maintenance therapy who are administered nelfinavir show a decrease in methadone plasma levels. However, the clinical relevance of this fact is seldom significant because it does not correlate with the appearance of opioid withdrawal symptoms (OWS). The objective of this study was to assess the clinical and pharmacokinetic interactions between methadone and nelfinavir.

PATIENTS AND METHOD

A prospective multicenter study of human immunodeficiency virus (HIV) positive patients on stable methadone therapy who initiated nelfinavir was performed. To determine the presence of OWS, 2 questionnaires, objective and subjective, were administered at weeks 1, 2, 3 and 4. A pharmacokinetic study measuring the minimal plasmatic concentration of methadone was done at baseline and at week 4.

RESULTS

29 patient were included. In 7 patients who underwent pharmacokinetic studies, the minimal plasmatic concentration of methadone decreased after 4 weeks of nelfinavir treatment from 6.889 ng/ml to 4.354 ng/ml (37%; p = 0.046). However the results of the questionnaires did not show the significant OWS, which precluded an increase in the dose of methadone.

CONCLUSIONS

In patients under stable methadone treatment, antiretroviral therapy including nelfinavir does not require any significant modification of methadone dose. The decrease in methadone plasmatic levels does not correlate with OWS.

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.

Pharmacokinetic interaction of nelfinavir and methadone in intravenous drug users

The effect of nelfinavir 1250 mg twice daily (b.i.d.) on the pharmacokinetics of methadone was determined in 14 HIV-negative methadone users.

DESIGN

The methadone dose (20-140 mg/day) was stabilized and fixed for at least 1 month before nelfinavir (1250 mg b.i.d. for 8 days) was added to the regimen. The concentrations of methadone enantiomers were measured before and during nelfinavir treatment, and the concentrations of nelfinavir and its active metabolite, AG1402, were measured during nelfinavir treatment. Adverse events and withdrawal/intoxication symptoms were monitored throughout the study.

RESULTS

Nelfinavir reduced the area under the concentration-time curve of R-methadone, and S-methadone by 43% and 51%, respectively. Nelfinavir and AG1402 concentrations were within the normal range of historical data, and no subject experienced withdrawal symptoms during the study or required dose adjustment during or after the study.

CONCLUSIONS

Although nelfinavir reduced the plasma concentrations of both R- and S-methadone, it seems to have no impact on the maintenance dose of methadone. A routine reduction of methadone dose is not recommended when coadministered with nelfinavir.

Lack of an effect of atazanavir on steady-state pharmacokinetics of methadone in patients chronically treated for opiate addiction

BACKGROUND

Effective antiretroviral treatment of opiate-addicted drug users with HIV infection often requires concomitant substance abuse treatment, commonly with methadone. Pharmacological interactions between antiretroviral drugs and methadone may result in opiate withdrawal or increased side effects.

OBJECTIVES

To determine if atazanavir, a once-daily protease inhibitor and moderate inhibitor of P450 CYP3A4, exhibited pharmacokinetic interactions with (R)-methadone.

METHODS

Methadone pharmacokinetic parameters were measured in 16 patients on chronic methadone therapy prior to and after 14 days of daily administration of atazanavir. Steady-state pharmacokinetic values for total, (R)- (active) and (S)- (inactive) isomers of methadone were derived from plasma concentrations versus time data. Symptoms of opiate withdrawal and excess were monitored.

RESULTS

For the active isomer (R)-methadone, the ratio of geometric means for coadministration with atazanavir relative to methadone alone were 1.03 [90% confidence interval (CI), 0.95-1.10] for the area under the concentration-time curve (AUC), 0.91 (90% CI, 0.84-1.00) for plasma maximal concentration and 1.11 (90% CI, 1.02-1.20) for plasma trough concentration. Confidence intervals for all three were within the no-effect or bioequivalence range of 0.80-1.25 for (R)-methadone. Inactive (S)-methadone was modestly reduced during atazanavir coadministration. Clinically relevant symptoms of opiate withdrawal or excess were not detected. Exposures to atazanavir were within range of previously reported values.

CONCLUSIONS

No clinically relevant pharmacokinetic interactions were found between atazanavir and methadone. Dosage adjustment need not be recommended for either methadone or atazanavir when co-administered to patients treated for opiate abuse and HIV disease.

Safety of lopinavir/ritonavir for the treatment of HIV-infection

Kaletra, a fixed-dose co-formulation of lopinavir/ritonavir, was the first boosted protease inhibitor developed for the treatment of HIV-infection. In September 2000, the US FDA granted Kaletra fast-track approval as data showed a higher efficacy in the treatment of HIV-infection than standard protease inhibitors of that time. Although potency was of major concern in the early years of highly active antiretroviral therapy (HAART), presently, with the perspective of HIV-infection becoming a chronic but well controllable disease, other issues begin to draw increased attention in the long-term management of HIV-infected patients. Among general health issues such as cardiovascular disease, metabolic disorders or hepatitis co-infection, the long-term toxicity and safety of HAART is an important concern when choosing antiretroviral drugs for each individual patient. In this review, the authors report on the safety of lopinavir/ritonavir in the treatment of HIV-infected patients, and focus on special patient groups and relevant safety issues.

Nevirapine significantly reduces the levels of racemic methadone and (R)-methadone in human immunodeficiency virus-infected patients

Methadone is metabolized by various isoforms of the cytochrome P450 family, which can be induced by many drugs, including nevirapine. The objective of the present study was to determine the effects of coadministration of nevirapine and methadone on the dose-adjusted areas under the concentration-time curves (AUCs) of racemic and (R)-methadone. Twenty-five human immunodeficiency virus-infected subjects taking stable single daily doses of racemic methadone or (R)-methadone were included in this prospective, single-crossover trial. At the baseline, nevirapine was either started as part of a new regimen containing two nucleoside reverse transcriptase inhibitors (NRTIs) or added to an ongoing NRTI regimen. Patients could increase their methadone doses if withdrawal symptoms developed. Twelve-hour pharmacokinetic profiles were obtained before and 28 days after the start of nevirapine treatment. The total concentrations of methadone and its inactive metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), in serum were determined by liquid chromatography-tandem mass spectrometry. Among the 20 evaluable patients, coadministration of nevirapine significantly decreased the mean dose-adjusted AUC of methadone by 41%. AUC reductions were similar for patients taking racemic methadone (37%; n = 11) and (R)-methadone (44%; n = 9). AUC changes ranged from mild increases in three patients to decreases of up to 70%. Fourteen of 20 patients required additional methadone due to withdrawal symptoms. However, the median dose increase was only 15%, which was less than that which would have been expected from the pharmacokinetic data. The AUC of EDDP increased significantly, by 35%. Methadone dose adjustments are justified when methadone is coadministered with nevirapine. Due to extensive variability, the adjustments must be tailored to the individual patient's needs.

Pharmacokinetics and Pharmacodynamics of Methadone Enantiomers After Coadministration with Amprenavir in Opioid-Dependent Subjects

STUDY OBJECTIVE

To investigate the steady-state pharmacokinetics of methadone enantiomers when coadministered with amprenavir.

DESIGN

Prospective, open-label, within-subject pharmacokinetic study.

SETTING

University research center.

SUBJECTS

Nineteen opioid-dependent, methadone-maintained, healthy individuals were enrolled.

INTERVENTION

On study day 1, subjects received their usual once-daily dose of methadone alone. On study days 2-11, they received the same once-daily methadone dose plus amprenavir 1200 mg twice/day. Serial blood samples were collected over 24 hours on study days 1 and 11 for measurement of plasma R- and S-methadone, and over 12 hours on day 11 for serum amprenavir concentrations.

MEASUREMENTS AND MAIN RESULTS

Standard pharmacokinetic parameters were determined from the concentrations and compared between the two treatments (methadone alone vs methadone with amprenavir). Subjects served as their own control for methadone comparisons, and amprenavir comparisons were made by using a historic control group (38 healthy men). Opioid-effect measures were assessed throughout the study. Coadministration of amprenavir with methadone resulted in a 3-4-hour delay in plasma R- and S-methadone enantiomer peak concentrations at steady state (Cmax-ss). The active R-methadone enantiomer area under the plasma concentration-time curve during a dosing interval (AUCt-ss, Cmax-ss, and the minimum plasma concentration at steady state (Cmin-ss) were decreased by 13%, 25%, and 21%, respectively, after coadministration of methadone and amprenavir. The inactive S-enantiomer AUCt-ss, Cmax-ss, and Cmin-ss were decreased by 40%, 48%, and 52%, respectively. No clinically significant changes were noted in opioid pharmacodynamic effects, and there was no evidence of opioid withdrawal. No methadone dosage was changed in any subject.

CONCLUSION

No a priori adjustment in methadone dosage is required during coadministration with amprenavir as there is only a small effect on R-methadone exposure and no evidence of opioid withdrawal.

Practical considerations for the clinical use of buprenorphine

Buprenorphine is a new and attractive medication option for many opioid-addicted adults and their physicians. Before initiating buprenorphine treatment, providers must be aware of such critical factors as how the medication works, its efficacy and safety profile, how it is used in opioid withdrawal as well as maintenance treatment, and how patients can best be selected, educated about buprenorphine, and monitored throughout treatment. This article reviews these important issues as well as requirements for physician and staff training and needs for additional research on this unique medication.

Effect of Tenofovir Disoproxil Fumarate on the Pharmacokinetics and Pharmacodynamics of Total, R-, and S-Methadone

STUDY OBJECTIVE

To evaluate the potential effect of tenofovir disoproxil fumarate (DF) on the pharmacokinetics of methadone.

DESIGN

Phase I, open-label, fixed-sequence, pharmacokinetic drug-drug interaction study.

SETTING

Clinical research center.

SUBJECTS

Fourteen volunteers receiving stable methadone maintenance therapy who were not infected with the human immunodeficiency virus.

INTERVENTION

Tenofovir DF was added to the subjects' methadone regimens.

MEASUREMENTS AND MAIN RESULTS

The pharmacokinetics of total, R-, and S-methadone were evaluated at baseline and after 2 weeks of daily tenofovir DF coadministration with a light meal. Steady-state tenofovir DF pharmacokinetics were evaluated at day 15. Bioequivalence testing was conducted of total, R-, and S-methadone area under the serum or plasma concentration-time curve during the 24-hour dosing interval at steady state (AUCss) and maximum concentration in serum or plasma (Cmax). Subjects were evaluated for changes in methadone pharmacodynamics by the Short Opiate Withdrawal Scale (SOWS) and pupillary diameter measurements at frequent intervals. Coadministration with tenofovir DF did not affect the pharmacokinetics of methadone. Geometric mean R-methadone systemic exposures, AUCss and Cmax, differed by 5% or less when methadone was dosed with tenofovir DF. Similar results were observed for S-methadone and for total methadone. Both AUCss and Cmax met the strict criteria for bioequivalence between the two study periods for total, R-, and S-methadone, indicating a lack of drug interaction when tenofovir DF was coadministered with methadone. No significant changes in SOWS scores or pupillary diameter measurements occurred, and no notable clinical adverse events were reported.

CONCLUSION

Tenofovir DF pharmacokinetics were comparable to previously reported values of tenofovir DF in HIV-infected patients. Coadministration of methadone with tenofovir DF did not alter the pharmacokinetics or pharmacodynamics of total, R-, or S-methadone. Tenofovir DF may be given as part of a once-daily antiretroviral regimen in patients receiving methadone maintenance therapy.

The protease inhibitor lopinavir-ritonavir may produce opiate withdrawal in methadone-maintained patients

This study examines the pharmacokinetic/pharmacodynamic interactions between (1) lopinavir-ritonavir (L/R), a fixed combination of protease inhibitors used for the treatment of HIV disease, and (2) ritonavir alone at the same dosage as that in the L/R formulation, with methadone, an opiate frequently used in substance abuse pharmacotherapy for opioid (heroin)-dependent injection drug users, many of whom are infected with HIV. L/R was associated with significant reductions in the methadone area under the concentration-time curve (P<.001), maximum concentration (P<.001), and minimum concentration (P<.001), as well as increased methadone oral clearance (P<.001) and increased opiate withdrawal symptoms (P=.013), whereas ritonavir use alone modestly and nonsignificantly increased methadone concentrations. Lopinavir is a potent inducer of methadone metabolism, and treatment with L/R requires clinical monitoring and increased methadone doses in some patients, whereas ritonavir has no significant effect on methadone metabolism.

Lopinavir/ritonavir: a review of its use in the management of HIV infection

Lopinavir is a novel protease inhibitor (PI) developed from ritonavir. Coadministration with low-dose ritonavir significantly improves the pharmacokinetic properties and hence the activity of lopinavir against HIV-1 protease. Coformulated lopinavir/ritonavir was developed for ease of administration and to ensure both drugs are taken together, as part of combination therapy with other antiretroviral agents. Coformulated lopinavir/ritonavir-based regimens provide adequate and durable suppression of viral load and sustained improvements in CD4+ cell counts, as demonstrated in randomised trials in antiretroviral therapy-naive and -experienced adults and children. To date, development of primary resistance to lopinavir/ritonavir has not been observed in 470 antiretroviral therapy-naive patients treated for >48 weeks. The lopinavir/ritonavir-based regimen was more effective than nelfinavir in antiretroviral therapy-naive HIV-1-infected patients in a phase III trial. The coformulation is also effective as 'salvage' therapy, as shown by low cross-resistance rates in patients who failed to respond to treatment with other PIs in phase II trials. Coformulated lopinavir/ritonavir was well tolerated in both antiretroviral therapy-naive and -experienced HIV-1-infected adults and children with low rates of study drug-related treatment discontinuations. The most common adverse event in adults associated with lopinavir/ritonavir was diarrhoea, followed by other gastrointestinal disturbances, asthenia, headache and skin rash. The incidence of moderate-to-severe adverse events in children was low, skin rash being the most common. Changes in body fat composition occurred with equal frequency in lopinavir/ritonavir- and nelfinavir-treated naive patients, through week 60 in a phase III study. Although laboratory abnormalities occurred with similar frequency in both treatment groups, triglycerides grade 3/4 elevations were significantly more frequent with lopinavir/ritonavir. Total cholesterol and triglycerides grade 3/4 elevations appear to occur more frequently in PI-experienced than in PI-naive lopinavir/ritonavir-treated patients. A number of clinically important drug interactions have been reported with lopinavir/ritonavir necessitating dosage adjustments of lopinavir/ritonavir and/or the interacting drugs, and several other drugs are contraindicated in patients receiving the coformulation.

CONCLUSION

Coformulated lopinavir/ritonavir is a novel PI that, in combination with other antiretroviral agents, suppresses plasma viral load and enhances immunological status in therapy-naive and -experienced patients with HIV-1 infection. Lopinavir/ritonavir appears more effective than nelfinavir in 'naive' patients and is also suitable for 'salvage' therapy, because of its high barrier to development of resistance. Given its clinical efficacy, a tolerability profile in keeping with this class of drugs, favourable resistance profile and easy-to-adhere-to administration regimen, coformulated lopinavir/ritonavir should be regarded as a first-line option when including a PI in the management of HIV-1 infection.

OVERVIEW OF PHARMACODYNAMIC PROPERTIES

Lopinavir/ritonavir is a coformulation of two structurally related protease inhibitor (PI) antiretroviral agents. Lopinavir is a highly potent and selective inhibitor of the HIV type 1 (HIV-1) protease, an essential enzyme for production of mature, infective virus. It acts by arresting maturation of HIV-1 thereby blocking its infectivity. Thus, the main antiviral action of lopinavir is to prevent subsequent infections of susceptible cells; it has no effect on cells with already integrated viral DNA. Lopinavir has an approximate, equals 10-fold higher in vitro activity against both wild-type and mutant HIV-1 proteases than ritonavir; however, its in vivo activity is greatly attenuated by a high first-pass hepatic metabolism. The low-dose ritonavir coadministered with lopinavir inhibits metabolic inactivation of lopinavir and acts only as its pharmacokinetic enhancer. Therefore, the antiretroviral activity of roviral activity of coformulated lopinavir/ritonavir 400/100mg twice daily is derived solely from lopinavir plasma concentrations. Combining lopinavir with low-dose ritonavir produces lopinavir concentrations far exceeding those needed to suppress 50% of in vitro and in vivo viral replication in CD4+ cells and monocyte/macrophages (main human reservoirs of HIV-1 infection). Thus far, no resistance to lopinavir has been detected in clinical trials in antiretroviral therapy-naive patients treated for up to 204 weeks and only 12% of HIV-1 strains from patients in whom prior treatment with multiple PIs have failed, have been observed to develop resistance to coformulated lopinavir/ritonavir. A strong negative correlation was found between the number of PI mutations at baseline and the viral response rates achieved with lopinavir/ritonavir-based regimens in PI-experienced patients, indicating that resistance to lopinavir increases with increasing number of PI mutations and that five PI mutations represent the clinically relevant genotypic breakpoint for lopinavir.

OVERVIEW OF PHARMACOKINETIC PROPERTIES

The absolute bioavailability of lopinavir coformulated with ritonavir in humans has not yet been established. Multiple-dosage absorption pharmacokinetics of lopinavir/ritonavir 400/100mg twice daily (the mean peak [C(max)] and trough [C(trough)] plasma concentrations at steady-state and the 12-hour area under the plasma concentration-time curve [AUC(12)] of either drug) were stable in antiretroviral therapy-naive and single PI-experienced adult patients receiving therapy over a 24-week evaluation period. The C(trough) values of lopinavir, achieved with lopinavir/ritonavir 400/100mg twice daily, were median 84-fold higher than the protein binding-adjusted 50% effective concentration (EC(50)) of lopinavir against wild-type HIV-1 in antiretroviral therapy-naive HIV-1-infected patients in a phase II study. Bioavailability of lopinavir administered in either the capsule or the liquid lopinavir/ritonavir formulation can be increased substantially with concurrent ingestion of food with moderate-to-high fat content. At steady state, lopinavir is approximately 98-99% plasma protein bound and the percentage of its unbound (i.e. pharmacologically active) fraction is dependent on total drug plasma concentration. Both lopinavir and ritonavir penetrate poorly into the human genital tracts and the cerebrospinal fluid. Both agents undergo extensive and rapid first-pass metabolism by hepatic cytochrome P450 (CYP) 3A4 isoenzyme. However, ritonavir also potently inhibits this enzyme and acts as a pharmacokinetic enhancer of lopinavir. The elimination half-life and apparent oral clearance of lopinavir average approximately 4-6 hours and approximately 6-7 L/h, respectively, with lopinavir/ritonavir 400/100mg twice daily administration. Less than 3% and 20% of the lopinavir dose is excreted unchanged in the urine and faeces, respectively. Limited data show similar pharmacokinetics of lopinavir in children as in adults.

DRUG INTERACTIONS

Coformulated lopinavir/ritonavir has the potential to interact with wide variety of drugs via several mechanisms, mostly involving the CYP enzymes. Coadministration of lopinavir/ritonavir is contraindicated with certain drugs (i.e. flecainide, propafenone, astemizole, terfenadine, ergot derivatives, cisapride, pimozide, midazolam and triazolam) that are highly dependent on CYP3A or CYP2D6 for clearance and for which elevated plasma concentrations are associated with serious and/or life-threatening events. Coadministration with lopinavir/ritonavir is also not recommended for drugs or herbal products (i.e. rifampicin [rifampin] and St. John's wort [Hypericum perforatum]) that may substantially reduce lopinavir plasma concentrations, or drugs whose plasma concentrations elevated by the coformulation may lead to serious adverse reactions (i.e. simvastatin and lovastatin). However, a recent study in healthy volunteers suggests that adequate lopinavir concentrations may be achieved during rifampicin coadministration by increasing the twice-daily dosage of lopinavir/ritonavir in conjunction with therapeutic drug monitoring. The liquid (but not the capsule) formulation of lopinavir/ritonavir contains 42.4% ethanol (v/v) and should not be coadministered with drugs capable of producing disulfiram-like reactions (e.g. disulfiram, metronidazole). Coadministration with saquinavir or indinavir requires no dosage adjustment, whereas coadministration with amprenavir, nevirapine or efavirenz requires a dosage increase of the coformulation typically by 33%. As the oral bioavailability of both didanosine and lopinavir/ritonavir is significantly affected by concurrent food ingestion, didanosine should be administered 1 hour before or 2 hours after lopinavir/ritonavir has been taken with food. Interactions between lopinavir/ritonavir and other nucleoside reverse transcriptase inhibitors (NRTIs) are not expected. The coformulation is also likely to increase plasma concentrations of non-antiretroviral drugs metabolised through the CYP3A pathway. To reduce the risk of their toxicity when coadministered with lopinavir/ritonavir, the recommended actions include: (i) monitoring of the drug plasma concentration (antiarrhythmics and immunosuppressants) or the international normalised ratio (warfarin); (ii) the use of alternative treatment (atorvastatin) or birth control methods (ethinylestradiol); and (iii) dosage adjustment (clarithromycin [only in patients with renal failure], rifabutin, dihydropyridine calcium-channel blockers, atorvastatin, ketoconazole and itraconazole). (ABSTRACT TRUNCATED)

Interactions between recreational drugs and antiretroviral agents

OBJECTIVE

To summarize existing data regarding potential interactions between recreational drugs and drugs commonly used in the management of HIV-positive patients.

DATA SOURCES

Information was obtained via a MEDLINE search (1966-August 2002) using the MeSH headings human immunodeficiency virus, drug interactions, cytochrome P450, medication names commonly prescribed for the management of HIV and related opportunistic infections, and names of commonly used recreational drugs. Abstracts of national and international conferences, review articles, textbooks, and references of all articles were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

Literature on pharmacokinetic interactions was considered for inclusion. Pertinent information was selected and summarized for discussion. In the absence of specific data, prediction of potential clinically significant interactions was based on pharmacokinetic and pharmacodynamic properties.

RESULTS

All protease inhibitors (PIs) and nonnucleoside reverse transcriptase inhibitors are substrates and potent inhibitors or inducers of the cytochrome P450 system. Many classes of recreational drugs, including benzodiazepines, amphetamines, and opioids, are also metabolized by the liver and can potentially interact with antiretrovirals. Controlled interaction studies are often not available, but clinically significant interactions have been observed in a number of case reports. Overdoses secondary to interactions between the "rave" drugs methylenedioxymethamphetamine (MDMA) or gamma-hydroxybutyrate (GHB) and PIs have been reported. PIs, particularly ritonavir, may also inhibit metabolism of amphetamines, ketamine, lysergic acid diethylmide (LSD), and phencyclidine (PCP). Case series and pharmacokinetic studies suggest that nevirapine and efavirenz induce methadone metabolism, which may lead to symptoms of opiate withdrawal. A similar interaction may exist between methadone and the PIs ritonavir and nelfinavir, although the data are less consistent. Opiate metabolism can be inhibited or induced by concomitant PIs, and patients should be monitored for signs of toxicity and/or loss of analgesia. PIs should not be coadministered with midazolam and triazolam, since prolonged sedation may occur.

CONCLUSIONS

Interactions between agents commonly prescribed for patients with HIV and recreational drugs can occur, and may be associated with serious clinical consequences. Clinicians should encourage open dialog with their patients on this topic, to avoid compromising antiretroviral efficacy and increasing the risk of drug toxicity.

[Recommendations of the Spanish AIDS Study Group (GESIDA) and the National Aids Plan (PNS) for antiretroviral treatment in adult patients with human immunodeficiency virus infection in 2002]

OBJECTIVE

To provide an update of recommendation on antiretroviral treatment (ART) in HIV-infected adults.Methods. These recommendations have been agreed by consensus by a committee of the spanish AIDS Study Group (GESIDA) and the National AIDS Plan. To do so, advances in the physiopathology of AIDS and the results on efficacy and safety in clinical trials, cohort and pharmacokinetics studies published in biomedical journals or presented at congresses in the last few years have been reviewed. Three levels of evidence have been defined according to the data source: randomized studies (level A), case-control or cohort studies (level B) and expert opinion (level C). Whether to recommend, consider, or not to recommend ART has been established for each situation.

RESULTS

Currently, ART with combinations of at least three drugs constitutes the treatment of choice in chronic HIV infection. In patients with symptomatic HIV infection, initiation of ART is recommended. In asymptomatic patients initiation of ART should be based on the CD41/mL lymphocyte count and on the plasma viral load (PVL): a) in patients with CD41 lymphocytes < 200 cells/mL, initiation of ART is recommended; b) in patients with CD41 lymphocytes between 200 and 300 cells/mL, initiation of ART should, in most cases, be recommended; however, it could be delayed when the CD41 lymphocyte count remains close to 350 cells/mL and the PVL is low, and c) in patients with CD41 lymphocytes > 350 cells/mL, initiation of ART can be delayed. The aim of ART is to achieve an undetectable PVL. Adherence to ART plays a role in the durability of the antiviral response. Because of the development of cross-resistance, the therapeutic options in treatment failure are limited. In these cases, genotypic analysis is useful. Toxicity limits ART. The criteria for ART in acute infection, pregnancy and postexposure prophylaxis and in the management of coinfection with HIV and hepatitis C and B virus are controversial.

CONCLUSIONS

The current approach to initiating ART is more conservative than in previous recommendations. In asymptomatic patients, the CD41 lymphocyte count is the most important reference factor for initiating ART. Because of the considerable number of drugs available, more sensitive monitoring methods (PVL) and the possibility of determining resistance, therapeutic strategies have become much more individualized.