Lack of a significant drug interaction between raltegravir and tenofovir

Pharmacokinetics of Antiretroviral Drugs in Older People Living with HIV: A Systematic Review

BACKGROUND AND OBJECTIVE

The life expectancy of people living with HIV (PLWHIV) has significantly improved in recent decades, mostly due to antiretroviral (ARV) therapy. Aging can affect the pharmacokinetics of drugs and, as a consequence, increase the risk of drug interactions and toxicity that may impact treatment. The aim of this study was to carry out a systematic review of the literature on the effect of aging on ARV pharmacokinetics.

METHODS

Searches were performed in the BVS, EMBASE and PUBMED databases until November 2022. All studies available in English, Spanish and Portuguese investigating the pharmacokinetics of ARV approved by the US Food and Drug Administration (FDA) from 2005 to 2020 were selected. Peer-reviewed publications were included if they met all criteria: adults (≥ 18 years of age) living with or without HIV; report any pharmacokinetic parameter or plasma concentration of at least one of the following ARVs: tenofovir alafenamide fumarate (TAF); doravirine (DOR), rilpivirine (RIL) and etravirine (ETR); darunavir (DRV), tipranavir (TPV) and fostemsavir (FTR); dolutegravir (DTG), raltegravir (RAL), bictegravir (BIC) and elvitegravir (EVG); maraviroc (MVC); ibalizumab (IBA); cobicistat (COBI). Pharmacokinetic parameters were reported stratified per age group: young adults (aged 18-49 years) or older (age ≥ 50 years) and all studies were evaluated for quality. The review protocol was registered in the PROSPERO database (registration number CRD42021236432).

RESULTS

Among 97 studies included, 20 reported pharmacokinetic evaluation in older individuals (age ≥ 50 years). Twenty five percent of the articles were phase I randomized clinical trials with HIV-negative participants and non-compartmental pharmacokinetic analysis presenting the parameters area under the curve (AUC) and peak drug concentration (Cmax). Seven age-stratified studies evaluated BIC, ETR, DRV, DTG, DOR and RAL. We found publications with discordant results for ETR and DTG pharmacokinetics in different age groups. DRV exposure was highly variable but modestly increased in aging PLWHIV. In contrast, no influence of age on BIC, DOR and RAL exposure was observed. A variability in pharmacokinetic parameters could be observed for the other ARVs (TAF and MVC) in different age groups.

CONCLUSION

Exposure to DRV increases modestly with age, while exposure to BIC, DOR and RAL appears to be unaffected by age. As the available evidence to confirm a potential effect of aging on ARV pharmacokinetics is limited, further studies are necessary.

Drug-drug interactions that alter the exposure of glucuronidated drugs: Scope, UDP-glucuronosyltransferase (UGT) enzyme selectivity, mechanisms (inhibition and induction), and clinical significance

Drug-drug interactions (DDIs) arising from the perturbation of drug metabolising enzyme activities represent both a clinical problem and a potential economic loss for the pharmaceutical industry. DDIs involving glucuronidated drugs have historically attracted little attention and there is a perception that interactions are of minor clinical relevance. This review critically examines the scope and aetiology of DDIs that result in altered exposure of glucuronidated drugs. Interaction mechanisms, namely inhibition and induction of UDP-glucuronosyltransferase (UGT) enzymes and the potential interplay with drug transporters, are reviewed in detail, as is the clinical significance of known DDIs. Altered victim drug exposure arising from modulation of UGT enzyme activities is relatively common and, notably, the incidence and importance of UGT induction as a DDI mechanism is greater than generally believed. Numerous DDIs are clinically relevant, resulting in either loss of efficacy or an increased risk of adverse effects, necessitating dose individualisation. Several generalisations relating to the likelihood of DDIs can be drawn from the known substrate and inhibitor selectivities of UGT enzymes, highlighting the importance of comprehensive reaction phenotyping studies at an early stage of drug development. Further, rigorous assessment of the DDI liability of new chemical entities that undergo glucuronidation to a significant extent has been recommended recently by regulatory guidance. Although evidence-based approaches exist for the in vitro characterisation of UGT enzyme inhibition and induction, the availability of drugs considered appropriate for use as 'probe' substrates in clinical DDI studies is limited and this should be research priority.

Para-aminosalicylic acid significantly reduced tenofovir exposure in human subjects: Mismatched findings from in vitro to in vivo translational research

AIMS

Tenofovir and para-aminosalicylic acid (PAS) may be coprescribed to treat patients with concomitant infections of human immunodeficiency virus and Mycobacterium tuberculosis bacteria. Both drugs are known to have remarkable renal uptake transporter-mediated clearance. Owing to the lack of clinical studies on drug-drug interaction between the 2 drugs, we conducted a translational clinical study to investigate the effect of PAS on tenofovir pharmacokinetics (PK).

METHODS

Initially, we studied in vitro renal uptake transporter-mediated drug-drug interactions using stably transfected cells with human organic anion transporters (OAT1 and OAT3). Later, we estimated clinical drug interactions using static and physiologically based PK modelling. Finally, we investigated the effects of PAS-calcium formulation (PAS-Ca) on tenofovir disoproxil fumarate PK in healthy male Korean subjects.

RESULTS

PAS inhibited OAT1- and OAT3-mediated tenofovir uptake in vitro. The physiologically based PK drug-drug interaction model suggested a 1.26-fold increase in tenofovir peak plasma concentration when coadministered with PAS. By contrast, an open-label, randomized, crossover clinical trial evaluating the effects of PAS-Ca on tenofovir PK showed significantly altered geometric mean ratio (90% confidence intervals) of maximum plasma concentration (C_max ) and area under the curve (AUC_0-inf ) by 0.33 (0.28-0.38) and 0.29 (0.26-0.33), respectively.

CONCLUSION

Our study findings suggest that the PAS-Ca formulation significantly reduced systemic exposure to tenofovir through an unexplained mechanism, which was contrary to the initial prediction. Caution should be exercised while predicting in vivo PK profiles from in vitro data, particularly when there are potential confounders such as pharmaceutical interactions.

Methotrexate Decreases Tenofovir Exposure in Antiretroviral-Suppressed Individuals Living With HIV

BACKGROUND

To mitigate increased risk of premature cardiovascular disease in antiretroviral therapy (ART) suppressed adults living with HIV (PWH), low-dose methotrexate (LDMTX) was evaluated in a multicenter randomized placebo controlled clinical trial of 176 PWH taking various ART regimens (ACTG A5314). Given shared methotrexate (MTX) and tenofovir (TFV) pharmacokinetic (PK) pathways, a substudy was conducted to investigate whether LDMTX alters TFV exposure.

METHODS

Adults virally suppressed on ART for >24 weeks were randomized to LDMTX or placebo. The first 66 participants taking a tenofovir disoproxil fumarate-containing regimen underwent intensive PK sampling over 24 hours after the second dose of LDMTX 10 mg or placebo. TFV and MTX levels were quantified using validated mass spectrometry methods. TFV PK between LDMTX and placebo groups were compared and MTX PK was characterized.

RESULTS

Forty-eight participants completed this substudy (n = 20 on LDMTX and 28 on placebo). Baseline characteristics were balanced except for protease inhibitor (PI)-use (25% in LDMTX and 43% in placebo groups). For TFV, AUC6 (primary endpoint), and AUC24,imputed, Cmax, and Cmin (secondary endpoints) were on average 22%, and 24%, 27%, and 31% less in the LDMTX versus placebo groups, with reductions in secondary endpoints reaching statistical significance. Additional analyses suggested a greater reduction in the absence of PI although not significant.

CONCLUSION

Lower TFV AUC24,imputed and Cmax indicates that LDMTX reduces TFV exposure in PWH. However, this change was modest, not warranting a change in TFV dosing at this time. Further studies of TFV PK with LDMTX, especially without PI co-administration, are warranted.

Are Standard Doses of Renally-Excreted Antiretrovirals in Older Patients Appropriate: A PBPK Study Comparing Exposures in the Elderly Population With Those in Renal Impairment

BACKGROUND AND OBJECTIVES

The elderly population receives the majority of prescription drugs but are usually excluded from Phase 1 clinical trials. Alternative approaches to estimate increases in toxicity risk or decreases in efficacy are therefore needed. This study predicted the pharmacokinetics (PK) of three renally excreted antiretroviral drugs in the elderly population and compared them with known exposures in renal impairment, to evaluate the need for dosing adjustments.

METHODS

The performance of the physiologically based pharmacokinetic (PBPK) models for tenofovir, lamivudine and emtricitabine were verified using clinical data in young and older subjects. Models were then used to predict PK profiles in a virtual population aged 20 to 49 years (young) and a geriatric population aged 65 to 74 years (elderly). Predicted exposure in the elderly was then compared with exposure reported for different degrees of renal impairment, where doses have been defined.

RESULTS

An increase in exposure (AUC) with advancing age was predicted for all drugs. The mean ratio of the increase in exposure were 1.40 for emtricitabine, 1.42 for lamivudine and 1.48 for tenofovir. The majority of virtual patients had exposures that did not require dosage adjustments. About 22% of patients on tenofovir showed exposures similar to that in moderate renal impairment, where dosage reduction may be required.

CONCLUSION

Comparison of the exposure in the elderly with exposure observed in patients with different levels of renal impairment, indicated that a dosage adjustment may not be required in elderly patients on lamivudine, emtricitabine and the majority of the patients on tenofovir. Clinical trials to verify these predictions are essential.

Effects of Tenofovir on the Single-Dose Pharmacokinetics of Intravenous Morinidazole in Healthy Chinese Subjects

The effects of multiple-dose administration of tenofovir disoproxil fumarate (TDF) on the pharmacokinetics of morinidazole (MOR) were compared in healthy subjects. MOR exposure was similar, with an area under the curve from 0 h to infinity (AUC_0-∞) treatment ratio for MOR+TDF/MOR of 1.01 (90% confidence interval, 0.97 to 1.06). No relevant differences were observed regarding plasma exposure of metabolites. Renal clearances of MOR and its metabolites were not affected by TDF. No unexpected safety or tolerability issues were observed.

Recent Advances in the Development of Integrase Inhibitors for HIV Treatment

PURPOSE OF THE REVIEW

The complex multistep life cycle of HIV allows it to proliferate within the host and integrate its genome in to the host chromosomal DNA. This provirus can remain dormant for an indefinite period. The process of integration, governed by integrase (IN), is highly conserved across the Retroviridae family. Hence, targeting integration is not only expected to block HIV replication but may also reveal new therapeutic strategies to treat HIV as well as other retrovirus infections.

RECENT FINDINGS

HIV integrase (IN) has gained attention as the most promising therapeutic target as there are no equivalent homologues of IN that has been discovered in humans. Although current nano-formulated long-acting IN inhibitors have demonstrated the phenomenal ability to block HIV integration and replication with extraordinary half-life, they also have certain limitations. In this review, we have summarized the current literature on clinically established IN inhibitors, their mechanism of action, the advantages and disadvantages associated with their therapeutic application, and finally current HIV cure strategies using these inhibitors.

Probenecid-Boosted Tenofovir: A Physiologically-Based Pharmacokinetic Model-Informed Strategy for On-Demand HIV Preexposure Prophylaxis

Multiple doses of tenofovir disoproxil fumarate (TDF) together with emtricitabine is effective for HIV preexposure prophylaxis (PrEP). TDF is converted to tenofovir (TFV) in circulation, which is subsequently cleared via tubular secretion by organic ion transporters (OATs; OAT1 and OAT3). Using in vitro kinetic parameters for TFV and the OAT1 and OAT3 inhibitor probenecid, a bottom‐up physiologically‐based pharmacokinetic model was successfully developed for the first time that accurately describes the probenecid–TFV interaction. This model predicted an increase in TFV plasma exposure by 60%, which was within 15% of the observed clinical pharmacokinetic data, and a threefold decrease in renal cells exposure following coadministration of a 600 mg TDF dose with 2 g probenecid. When compared with multiple‐dose regimens, a single‐dose probenecid‐boosted TDF regimen may be effective for HIV PrEP and improve adherence and safety by minimizing TFV‐induced nephrotoxicity by reducing TFV accumulation in renal cells.

Prediction of renal transporter-mediated drug-drug interactions for a drug which is an OAT substrate and inhibitor using PBPK modelling

A PBPK modelling approach was used to predict organic anion transporter (OAT) mediated drug-drug interactions involving S44121, a substrate and an inhibitor of OAT1 and OAT3. Model predictions were then compared to the results of a clinical DDI study which was carried out to investigate the interaction of S44121 with probenecid, tenofovir and ciprofloxacin. PBPK models were developed and qualified using existing clinical data, and inhibition constants were determined in vitro. The model predictions for S44121 as an OAT inhibitor were similar to the results obtained from the clinical DDI study, with no interaction observed for tenofovir or ciprofloxacin in the presence of S44121. An observed AUC ratio of 2.2 was obtained for S44121 in the presence of probenecid, which was slightly higher than the model predicted AUC ratio of 1.6. A DDI study in the monkey was also carried out for the interaction between S44121 and probenecid, since the monkey has previously been reported to be a good preclinical model for OAT-mediated DDI. However, this study highlighted a species difference in the major route of S44121 elimination between monkey (mainly hepatic metabolism) and human (mainly renal excretion of unchanged drug), rendering a comparison between the two DDI studies difficult. Overall, for S44121 the PBPK modelling approach gave a better prediction of the extent of DDI than the static predictions based on inhibitor C_max and IC₅₀, therefore this can be considered a potentially valuable tool within drug development.

Pharmacokinetic and pharmacodynamic evaluation of raltegravir and experience from clinical trials in HIV-positive patients

INTRODUCTION

Raltegravir was the first available integrase inhibitor for treating HIV-positive patients. This review aims to provide an overview of its role in the management of HIV-1 infection, highlighting its key pharmacokinetic and pharmacodynamic properties.

AREAS COVERED

This review covers material searched and obtained through Medline and PubMed up to April 2015.

EXPERT OPINION

Raltegravir for its tolerability, efficacy, few drug-to-drug interactions and for the amount of available data in difficult subgroups of patients is a key drug in the antiretroviral armamentarium. For its weak genetic barrier to resistance and erratic pharmacokinetic profile, it should be administered twice daily and with fully active companion antiretrovirals.

Pharmacokinetic drug-drug interaction study between raltegravir and citalopram

BACKGROUND

Depression is the most common mental health disorder among HIV-infected patients. When treating HIV-infected patients with a selective serotonin reuptake inhibitor (SSRI), potential drug-drug interactions with antiretroviral agents have to be taken into account. We investigated the two-way pharmacokinetic drug-drug interaction and tolerability of concomitant administration of the SSRI citalopram and the HIV-1 integrase inhibitor raltegravir in healthy volunteers.

METHODS

An open-label, crossover, two-period trial was conducted in 24 healthy volunteers. Subjects received the following treatments: citalopram 20 mg once daily for 2 weeks followed by the combination with raltegravir 400 mg twice daily for 5 days and after a washout period raltegravir 400 mg twice daily for 5 days. Intensive steady-state pharmacokinetic blood sampling was performed. Geometric mean ratios (GMRs) of the combination versus the reference treatment and 90% CIs were calculated for the area under the plasma concentration-time curve (AUC). CYP2C19 genotyping was performed because it influences N-demethylation of citalopram to desmethylcitalopram.

RESULTS

A total of 22 healthy volunteers completed the trial. GMRs (90% CI) were 1.00 (0.98, 1.03) for citalopram AUC0-24 h, 0.99 (0.88, 1.12) for desmethylcitalopram AUC0-24 h and 0.77 (0.50, 1.19) for raltegravir AUC0-12 h. Raltegravir plasma concentration 12 h after intake (C12 h) did not change with concomitant use of citalopram. Within each CYP2C19 phenotype subgroup the citalopram metabolite-to-parent ratio, which is a measure for metabolic enzyme activity, was not influenced by concomitant raltegravir use.

CONCLUSIONS

Raltegravir does not influence the pharmacokinetics of citalopram and desmethylcitalopram. Citalopram did not change the pharmacokinetics of raltegravir in a clinically meaningful way. The combination was well tolerated and can be administered without dose adjustments. ClinicalTrials.gov NCT01978782.

Physiologically-based pharmacokinetic modeling of renally excreted antiretroviral drugs in pregnant women

AIM

Physiological changes during pregnancy can affect drug disposition. Anticipating these changes will help to maximize drug efficacy and safety in pregnant women. Our objective was to determine if physiologically-based pharmacokinetics (PBPK) can accurately predict changes in the disposition of renally excreted antiretroviral drugs during pregnancy.

METHODS

Whole body PBPK models were developed for three renally excreted antiretroviral drugs, tenofovir (TFV), emtricitabine (FTC) and lamivudine (3TC). To assess the impact of pregnancy on PK, time-varying pregnancy-related physiological parameters available within the p-PBPK Simcyp software package were used. Renal clearance during pregnancy followed glomerular filtration changes with or without alterations in secretion. PK profiles were simulated and compared with observed data, i.e. area under the curves (AUC), peak plasma concentrations (Cmax ) and oral clearances (CL/F).

RESULTS

PBPK models successfully predicted TFV, FTC and 3TC disposition for non-pregnant and pregnant populations. Both renal secretion and filtration changed during pregnancy. Changes in renal clearance secretion were related to changes in renal plasma flow. The maximum clearance increases were approximately 30% (TFV 33%, FTC 31%, 3TC 29%).

CONCLUSIONS

Pregnancy PBPK models are useful tools to quantify a priori the drug exposure changes during pregnancy for renally excreted drugs. These models can be applied to evaluate alternative dosing regimens to optimize drug therapy during pregnancy.

The role of drug transporters in the kidney: lessons from tenofovir

Tenofovir disoproxil fumarate, the prodrug of nucleotide reverse transcriptase inhibitor tenofovir, shows high efficacy and relatively low toxicity in HIV patients. However, long-term kidney toxicity is now acknowledged as a modest but significant risk for tenofovir-containing regimens, and continuous use of tenofovir in HIV therapy is currently under question by practitioners and researchers. Co-morbidities (hepatitis C, diabetes), low body weight, older age, concomitant administration of potentially nephrotoxic drugs, low CD4 count, and duration of therapy are all risk factors associated with tenofovir-associated tubular dysfunction. Tenofovir is predominantly eliminated via the proximal tubules of the kidney, therefore drug transporters expressed in renal proximal tubule cells are believed to influence tenofovir plasma concentration and toxicity in the kidney. We review here the current evidence that the actions, pharmacogenetics, and drug interactions of drug transporters are relevant factors for tenofovir-associated tubular dysfunction. The use of creatinine and novel biomarkers for kidney damage, and the role that drug transporters play in biomarker disposition, are discussed. The lessons learnt from investigating the role of transporters in tenofovir kidney elimination and toxicity can be utilized for future drug development and clinical management programs.

Long-term efficacy and safety of raltegravir in the management of HIV infection

Raltegravir is an integrase strand-transfer inhibitor approved for the treatment of HIV infection. It was the first medication in a novel class of antiretroviral agents to be approved for use in the United States in 2007. Raltegravir exhibits potent activity against wild-type HIV-1, but resistance development has been noted through three different pathways. It is metabolized primarily through uridine diphosphate glucuronosyltransferase 1A1 and has a single inactive glucuronide metabolite. Raltegravir is not a substrate, inhibitor, or inducer of cytochrome P450 enzymes and exhibits low potential for drug–drug interactions; however, strong uridine diphosphate glucuronosyltransferase 1A1 inhibitors or inducers can alter the pharmacokinetics of raltegravir. It is well tolerated, and the most commonly reported adverse effects include headache, nausea, and diarrhea. Serious adverse effects with raltegravir are rare but include rhabdomyolysis and severe skin and hypersensitivity reactions. It has been approved for use in both treatment-naïve and treatment-experienced patients and is a preferred first-line agent in both United States and European HIV treatment guidelines. Although initial approval was granted on 48-week data, 5-year clinical data have recently been published. This article reviews the data supporting long-term efficacy and safety of raltegravir in the treatment of HIV infection.

Validation of an UPLC-MS/MS method for quantitative analysis of raltegravir in human plasma samples

BACKGROUND

An ultra-performance liquid chromatography-tandem mass spectrometry method was developed for the quantification of raltegravir (RTG) plasma concentrations in samples from HIV patients treated with the drug.

METHODS

Plasma samples were extracted by liquid-liquid extraction followed by evaporation to dryness and reconstitution in mobile phase. The chromatographic separation was carried out on an AQUITY UPLC C18 column with an isocratic mobile phase consisting of water containing 0.1% formic acid and acetonitrile containing 0.1% formic acid (50:50 vol/vol). The detection was performed on a triple quadrupole tandem mass spectrometer using multi-reaction monitoring via electrospray ionization source with positive ionization mode.

RESULTS

Under these conditions, a single chromatographic run could be completed within 1 minute. The method was validated by estimating the precision and the accuracy for inter- and intra-day analysis in the concentration range of 5-2560 ng/mL. The method was linear over the investigated range with all the correlation coefficients, r, greater than 0.995 on 5 replicates. The intra- and inter-day precision (percentage of coefficient of variation) ranged from 2.4% to 11.2%, and the inaccuracy (percent of relative standard deviation) ranged from 2.5% to 12.9%. No significant matrix effect was observed. The mean recovery value of RTG was 80%.

CONCLUSIONS

This rapid and sensitive method was validated and could be applied to pharmacokinetic studies for the determination of RTG concentrations in human plasma samples.

Raltegravir has a low propensity to cause clinical drug interactions through inhibition of major drug transporters: an in vitro evaluation

Raltegravir (RAL) is a human immunodeficiency virus type 1 (HIV-1) integrase inhibitor approved to treat HIV infection in adults in combination with other antiretrovirals. The potential of RAL to cause transporter-related drug-drug interactions (DDIs) as an inhibitor has not been well described to date. In this study, a series of in vitro experiments were conducted to assess the inhibitory effects of RAL on major human drug transporters known to be involved in clinically relevant drug interactions, including hepatic and renal uptake transporters and efflux transporters. For hepatic uptake transporters, RAL showed no inhibition of organic anion-transporting polypeptide 1B1 (OATP1B1), weak inhibition of OATP1B3 (40% inhibition at 100 μM), and no inhibition of organic cation transporter 1 (OCT1). Studies of renal uptake transporters showed that RAL inhibited organic anion transporters 1 and 3 (OAT1 and OAT3) with 50% inhibitory concentrations (IC50s) (108 μM and 18.8 μM, respectively) well above the maximum concentration of drug in plasma (Cmax) at the clinical 400-mg dose and did not inhibit organic cation transporter 2 (OCT2). As for efflux transporters, RAL did not inhibit breast cancer resistance protein (BCRP) and showed weak inhibition of multidrug and toxin extrusion protein 1 (MATE1) (52% inhibition at 100 μM) and MATE2-K (29% inhibition at 100 μM). These studies indicate that at clinically relevant exposures, RAL does not inhibit or only weakly inhibits hepatic uptake transporters OATP1B1, OATP1B3, and OCT1, renal uptake transporters OCT2, OAT1, and OAT3, as well as efflux transporters BCRP, MATE1, and MATE2-K. The propensity for RAL to cause DDIs via inhibition of these transporters is therefore considered low.

Variability of raltegravir plasma levels in the clinical setting

Therapeutic drug monitoring of raltegravir Ctrough levels was carried out in the setting of the Raltegravir Switch for Toxicity or Adverse events (RASTA) trial, a randomized pilot study exploring a 48-week safety and efficacy of treatment switch to raltegravir associated with tenofovir/emtricitabine or abacavir/lamivudine in patients with regimens with optimal virologic control. Blood sampling for measurement of raltegravir plasma levels was carried out at weeks 4, 12, 24, 36 and 48. Plasma samples were analysed by a recently developed and validated UPLC-MS method. A total of 164 samples from 39 patients were assayed. Analysis for intra- and inter-subject variability was restricted to those patients with 4 or more determinations, including 30 patients and 142 determinations. The intra- and inter-subject variability measures were 85.9 and 124.6%, respectively, with an intra-/inter-subject variability ratio of 69%. We also analysed data from a subset of patients with well-documented adherence to protocol, defined as protocol compliant population, including 21 patients and 93 determinations. In this subpopulation, we estimated intra- and inter-subject variability of 79.87% and 110%, respectively, with an intra-/inter-subject variability ratio of 72.6%. This study confirms the notion that raltegravir is a highly variable drug according to the European Medicines Agency criteria. While this condition does not favour the adoption of therapeutic drug monitoring in the clinical practice, the latter is deemed useful in patients with drug plasma concentrations below or near the threshold level of efficacy (since intracellular raltegravir levels might be as low as 5% of the corresponding plasma levels), or to identify drug-drug interactions of potential clinical relevance.

Raltegravir central nervous system tolerability in clinical practice: results from a multicenter observational study

Central nervous system (CNS) symptoms have been reported in clinical trials and case reports in patients receiving raltegravir. We investigated CNS symptoms in 453 HIV-infected patients. Of these 47 (10.4%) developed at least one drug-related CNS symptom. Predictors of CNS symptoms were concomitant therapy with tenofovir or with proton pump inhibitors that can increase raltegravir concentration. Thus, our data suggest a possible correlation between high raltegravir plasma concentrations and CNS symptoms, and therefore their monitoring in clinical practice.

Lack of a clinically significant drug-drug interaction in healthy volunteers between the hepatitis C virus protease inhibitor boceprevir and the HIV integrase inhibitor raltegravir

BACKGROUND

Patients coinfected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV) are likely to use both HIV and HCV treatment. Drug-drug interactions have been demonstrated between boceprevir, an HCV protease inhibitor, and frequently prescribed antiretroviral drugs, such as efavirenz and boosted HIV protease inhibitors. Concomitant administration of boceprevir with these drugs should be avoided. This study was designed to investigate the absence of a drug-drug interaction between boceprevir and raltegravir, an HIV integrase inhibitor.

METHODS

This was an open-label, randomized, 2-period, crossover phase 1 trial in 24 healthy volunteers. All subjects were randomly assigned to receive boceprevir 800 mg every 8 hours for 9 days plus a single dose of raltegravir 400 mg on day 10 followed by a washout period and a single dose of raltegravir 400 mg on day 38, or the same medication in reverse order. Blood samples for pharmacokinetics were collected and pharmacokinetic parameters were calculated.

RESULTS

The geometric mean (GM) of raltegravir area under the concentration-time curve (AUC)(0-12h) and maximum plasma concentration (C(max)) for raltegravir + boceprevir vs raltegravir alone were 4.27 (95% confidence interval [CI], 3.22-5.66) vs 4.04 (95% CI, 3.09-5.28) mg * hour/L and 1.06 (95% CI, .76-1.49) vs 0.93 (95% CI, .70-1.23) mg/L, respectively. GM ratio estimates of raltegravir AUC(0-12h) and C(max) for raltegravir + boceprevir vs raltegravir alone were 1.04 (90% CI, .88-1.22) and 1.11 (90% CI, .91-1.36), respectively. The GM of boceprevir AUC(0-8h), C(max), and C(8h) were 5.45 (95% CI, 5.11-5.81) mg * hour/L, 1.88 (95% CI, 1.72-2.06) mg/L, and 0.09 (95% CI, .07-.11) mg/L, respectively. These data are comparable to those from historical controls.

CONCLUSIONS

Due to the absence of a clinically significant drug interaction, raltegravir can be recommended for combined HIV/HCV treatment including boceprevir.

CLINICAL TRIALS REGISTRATION

NCT01288417.

Pharmacology of HIV integrase inhibitors

PURPOSE OF REVIEW

The purpose of this study is to review recent and relevant pharmacology data for three HIV integrase inhibitors: raltegravir (marketed), dolutegravir, and elvitegravir (both in phase III drug development).

RECENT FINDINGS

Data from January 2011 to April 2012 were evaluated. These data better characterized integrase inhibitor pharmacokinetics, assessed dosing regimens, and investigated previously undescribed drug-drug interactions. Due to formulation challenges, raltegravir inter-patient and intra-patient pharmacokinetic variability is high. Twice-daily 400  mg dosing has been shown to be clinically superior to 800  mg once-daily dosing. A pediatric formulation of raltegravir with less variable pharmacokinetics and greater bioavailability was US Food and Drug Administration (US FDA)-approved in December 2011. Cobicistat-boosted elvitegravir, and the second-generation integrase inhibitor dolutegravir, have lower pharmacokinetic variability and are dosed once daily. Dolutegravir drug interactions are similar to raltegravir, whereas boosted elvitegravir participates in additional CYP3A-mediated interactions.

SUMMARY

Raltegravir's potent antiretroviral activity has resulted in widespread use in both treatment-naïve and experienced patients. Dolutegravir and cobicistat-boosted elvitegravir have some pharmacokinetic advantages. Pharmacokinetic data in special populations (pregnancy, pediatrics) to optimize dosing are still required.

Update on raltegravir and the development of new integrase strand transfer inhibitors

Raltegravir (RAL) is the first antiretroviral in the integrase strand transfer inhibitors (INSTI) class. The use of RAL has expanded since its approval in October 2007 for multidrug-resistant human immunodeficiency virus type 1 infection in adults. RAL is now a guideline-preferred treatment option for antiretroviral-naïve patients, indicated for treatment in adolescents, and is being studied as an integral part of nucleoside sparing regimens. The development of resistance and the need for a once-daily dosing option has led to the development of new INSTIs, including elvitegravir and dolutegravir. Elvitegravir is being studied in a promising once-daily single-tablet regimen with tenofovir, emtricitabine, and the investigational pharmacoenhancer cobicistat. The development of cobicistat and the new once-daily INSTIs may revolutionize the treatment of human immunodeficiency virus type 1 infection. This article reviews the current literature on raltegravir and new developments in the INSTI class.

Role of raltegravir in HIV-1 management

OBJECTIVE

To review the literature concerning the role of raltegravir in the treatment of HIV-1 in antiretroviral (ARV)-experienced and ARV-naïve patients.

DATA SOURCES

A PubMed search was conducted for published data through March 2012 using the search terms raltegravir, MK-0518, and integrase strand transfer inhibitor. An additional search of International Pharmaceutical Abstracts for unpublished data, including data from the Infectious Diseases Society of America, the Conference on Retroviruses and Opportunistic Infections, the International AIDS Society, and the Interscience Conference on Antimicrobial Agents and Chemotherapy, was conducted using similar search terms.

STUDY SELECTION AND DATA EXTRACTION

In vitro and in vivo Phase 2, Phase 3, and postmarketing studies available in English, evaluating antiretroviral regimens that contain raltegravir for the treatment of HIV-1 infection in both ARV-naïve and ARV-experienced patients, were evaluated. Studies assessing raltegravir pharmacokinetics and pharmacodynamics were included for review.

DATA SYNTHESIS

The nucleoside-based regimen of raltegravir with tenofovir/emtricitabine provides an effective first-line treatment option. However, nucleoside-sparing regimens appear unfavorable in ARV-naïve subjects and should be reserved for patients with limited treatment options. Raltegravir used with optimized background therapy provides an alternative regimen for ARV-experienced patients. This review describes the available in vitro and in vivo data on raltegravir potency, defined as the ability to achieve undetectable viral load, and safety profile, as well as comparison to standard HIV-1 therapies.

CONCLUSIONS

Raltegravir has demonstrated potent antiretroviral activity against HIV-1 in both ARV-naïve and ARV-experienced subjects, with the benefits of a favorable adverse effect profile and minimal drug interactions. Raltegravir must be dosed twice daily, as once daily raltegravir displays decreased virologic efficacy compared to twice daily dosing. However, the ongoing development of new integrase strand transfer inhibitors may provide potent once daily regimens.

Population pharmacokinetic analysis and pharmacogenetics of raltegravir in HIV-positive and healthy individuals

The objectives of this study were to characterize raltegravir (RAL) population pharmacokinetics in HIV-positive (HIV(+)) and healthy individuals, identify influential factors, and search for new candidate genes involved in UDP glucuronosyltransferase (UGT)-mediated glucuronidation. The pharmacokinetic analysis was performed with NONMEM. Genetic association analysis was performed with PLINK using the relative bioavailability as the phenotype. Simulations were performed to compare once- and twice-daily regimens. A 2-compartment model with first-order absorption adequately described the data. Atazanavir, gender, and bilirubin levels influenced RAL relative bioavailability, which was 30% lower in HIV(+) than in healthy individuals. UGT1A9*3 was the only genetic variant possibly influencing RAL pharmacokinetics. The majority of RAL pharmacokinetic variability remains unexplained by genetic and nongenetic factors. Owing to the very large variability, trough drug levels might be very low under the standard dosing regimen, raising the question of a potential relevance of therapeutic drug monitoring of RAL in some situations.

Acceptable plasma concentrations of raltegravir and etravirine when administered by gastrostomy tube in a patient with advanced multidrug-resistant human immunodeficiency virus infection

STUDY OBJECTIVE

To determine whether the absorption of four antiretroviral agents-raltegravir, etravirine, emtricitabine, and tenofovir-is compromised when administered by gastrostomy tube.

DESIGN

Pharmacokinetic analysis.

SETTING

University medical center.

PATIENT

A 52-year-old African-American man coinfected with advanced multidrug-resistant human immunodeficiency virus (HIV) and chronic hepatitis B, who was receiving treatment with raltegravir, etravirine, emtricitabine, and tenofovir, and developed ulcerative esophagitis with perforation, requiring a gastrostomy tube.

MEASUREMENTS AND MAIN RESULTS

Due to the patient's esophageal perforations, all nutrition and drug therapy had to be provided by gastrostomy tube. As his antiretroviral regimen of raltegravir, etravirine, and emtricitabine-tenofovir was not available in liquid or powder formulations, the oral tablets were crushed or dispersed and mixed with water, then administered by gastrostomy tube. To ensure that the absorption of the drugs was sufficient for antiretroviral response, plasma samples were collected at 2 hours and 12 hours after dosing, and drug concentrations were quantitated by using validated assays. The 2- and 12-hour postdose plasma concentrations were 1220 and 446 ng/ml for raltegravir, 212 and 274 ng/ml for etravirine, 1148 and 164 ng/ml for emtricitabine, and 320 and 94 ng/ml for tenofovir, respectively. The patient's plasma concentrations were then compared with those in published pharmacokinetic studies of oral regimens administered to HIV-infected persons and healthy volunteers. Overall, the plasma concentrations of the antiretrovirals administered by gastrostomy tube were similar to published values. No drug toxicities were observed in this patient.

CONCLUSION

These pharmacokinetic data suggest that absorption of raltegravir, etravirine, emtricitabine, and tenofovir was not compromised when the drugs were administered by gastrostomy tube. These findings provide a basis for further investigation of the pharmacokinetics, safety, tolerance, and antiretroviral response to raltegravir, etravirine, and emtricitabine-tenofovir when the oral route of administration is not possible.

Pharmacokinetics of and short-term virologic response to low-dose 400-milligram once-daily raltegravir maintenance therapy

Because studies showed similar viral suppression with lower raltegravir doses and because Asians usually have high antiretroviral concentrations, we explored low-dose raltegravir therapy in Thais. Nineteen adults on raltegravir at 400 mg twice daily (BID) with HIV RNA loads of <50 copies/ml were randomized to receive 400 mg once daily (QD) or 800 mg QD for 2 weeks, followed by the other dosing for 2 weeks. Intensive pharmacokinetic analyses were performed, and HIV RNA was monitored. Two patients were excluded from the 400-mg QD analysis due to inevaluable pharmacokinetic data. The mean patient weight was 58 kg. Mean pharmacokinetic values were as follows: for raltegravir given at 400 mg BID, the area under the concentration-time curve from 0 to 12 h (AUC₀₋₁₂) was 15.6 mg/liter-h and the minimum plasma drug concentration (C(trough)) was 0.22 mg/liter; for raltegravir given at 800 mg QD, the AUC₀₋₂₄ was 33.6 mg/liter-h and the C(trough) was 0.06 mg/liter; and for raltegravir given at 400 mg QD, the AUC₀₋₂₄ was 18.6 mg/liter-h and the C(trough) was 0.08 mg/liter. The HIV RNA load was <50 copies/ml at each dose level. Compared to the adjusted AUC₀₋₂₄ for Westerners on raltegravir at 400 mg BID, Thais on the same dose had double the AUC₀₋₂₄ and those on raltegravir at 400 mg QD had a similar AUC₀₋₂₄. More patients had a C(trough) of <0.021 mg/liter on raltegravir at 400 mg QD (9/17 patients) than on raltegravir at 800 mg QD (1/19 patients) or 400 mg BID (0/19 patients). Seventeen patients used raltegravir at 400 mg QD for a median of 35 weeks; two had confirmed HIV RNA loads between 50 and 200 copies/ml, and both had low C(trough) values. Low-dose raltegravir could be a cost-saving option for maintenance therapy in Asians or persons with low body weight. However, raltegravir at 400 mg QD was associated with a low C(trough) and with a risk for HIV viremia. Raltegravir at 200 or 300 mg BID should be studied, but new raltegravir formulations will be needed.

Raltegravir once daily or twice daily in previously untreated patients with HIV-1: a randomised, active-controlled, phase 3 non-inferiority trial

BACKGROUND

Twice-daily raltegravir with once-daily tenofovir-emtricitabine is an effective initial antiretroviral regimen for patients with HIV-1. On the basis of pharmacokinetic data suggesting efficacy of once-daily raltegravir and because adherence is often improved with once-daily dosing, we aimed to compare these dosing schedules.

METHODS

In our international, double-blind, randomised, phase 3 non-inferiority study, we enrolled antiretroviral-naive patients with HIV RNA loads of more than 5000 copies per mL and no baseline resistance to tenofovir or emtricitabine at 83 centres worldwide. We randomly allocated patients (1:1) by use of a computer-generated sequence to receive raltegravir once daily (two 400 mg tablets taken together every 24 h), or twice daily (one 400 mg tablet every 12 h), both in combination with once-daily co-formulated tenofovir 300 mg plus emtricitabine 150 mg. The primary outcome was virological response at 48 weeks (viral RNA loads <50 copies per mL) in patients who received at least one dose of study drug, counting non-completers as failure. We assessed non-inferiority in terms of the proportion of patients in both treatment groups who achieved the primary outcome, with a non-inferiority margin of -10%. This study is registered with ClinicalTrials.gov, number NCT00745823.

FINDINGS

From Oct 15, 2008, to Nov 2, 2009, we randomly allocated 775 patients, of whom 382 (99%) of 386 patients in the once-daily group and 388 (99%) of 389 in the twice-daily group received at least one dose of study drug. At baseline, 304 (39%) of 770 treated patients had viral loads of more than 100,000 copies per mL and 188 (24%) had CD4 cell counts of fewer than 200 cells per μL. 318 (83%) of 382 patients in the once-daily group had virological response compared with 343 (89%) of 386 in the twice-daily group (difference -5·7%, 95% CI -10·7 to -0·83; p=0·044). Serious adverse events were reported in 26 (7%) of 382 once-daily recipients and 40 (10%) of 388 twice-daily recipients, and adverse events leading to discontinuation occurred in four (1%) patients in each group.

INTERPRETATION

Despite high response rates with both regimens, once-daily raltegravir cannot be recommended in place of twice-daily dosing.

FUNDING

Merck.

Role of raltegravir in the management of HIV-1 infection

The development of multiple agents with potent antiretroviral activity against HIV has ushered in a new age of optimism in the management of patients infected with the virus. However, the viruses' dynamic ability to develop resistance against these agents necessitates the investigation of novel targets for viral suppression. Raltegravir represents a first-in-class agent targeting the HIV integrase enzyme, which is responsible for integration of virally encoded DNA into the host genome. Over the last 5 years, clinical trials data has demonstrated an increasing role for raltegravir in the management of both treatment-experienced and treatment-naïve HIV-1-infected patients. This review focuses on the evidence supporting raltegravir's efficacy in an array of clinical settings. Other HIV-1 integrase inhibitors in development are also briefly discussed.

Raltegravir: the first HIV-1 integrase strand transfer inhibitor in the HIV armamentarium

Raltegravir is the first integrase strand transfer inhibitor approved for the treatment of HIV-1 infection. As the first agent in this new class of antiretroviral therapies, raltegravir has demonstrated safety and efficacy in treatment-naive as well as heavily pretreated HIV-infected patients failing therapy with multidrug-resistant virus. Raltegravir has a favorable drug interaction profile that permits both administration to a wide, demographically diverse patient population and coadministration with many other therapeutic agents, including antiretroviral agents and supportive medications, without restrictions or dose adjustment. Data through 96 weeks of follow-up in three phase III studies, protocol 021 (STARTMRK) in treatment-naive patients, and protocols 018 (BENCHMRK-1) and 019 (BENCHMRK-2) in treatment-experienced patients, demonstrated the potent and durable antiretroviral and immunologic effects and the favorable long-term safety profile of raltegravir in both treatment-naive and treatment-experienced patients. Raltegravir represents an important addition to the current armamentarium for the treatment of HIV infection.

Raltegravir is a substrate for SLC22A6: a putative mechanism for the interaction between raltegravir and tenofovir

The identification of transporters of the HIV integrase inhibitor raltegravir could be a factor in an understanding of the pharmacokinetic-pharmacodynamic relationship and reported drug interactions of raltegravir. Here we determined whether raltegravir was a substrate for ABCB1 or the influx transporters SLCO1A2, SLCO1B1, SLCO1B3, SLC22A1, SLC22A6, SLC10A1, SLC15A1, and SLC15A2. Raltegravir transport by ABCB1 was studied with CEM, CEM(VBL100), and Caco-2 cells. Transport by uptake transporters was assessed by using a Xenopus laevis oocyte expression system, peripheral blood mononuclear cells, and primary renal cells. The kinetics of raltegravir transport and competition between raltegravir and tenofovir were also investigated using SLC22A6-expressing oocytes. Raltegravir was confirmed to be an ABCB1 substrate in CEM, CEM(VBL100), and Caco-2 cells. Raltegravir was also transported by SLC22A6 and SLC15A1 in oocyte expression systems but not by other transporters studied. The K(m) and V(max) for SLC22A6 transport were 150 μM and 36 pmol/oocyte/h, respectively. Tenofovir and raltegravir competed for SLC22A6 transport in a concentration-dependent manner. Raltegravir inhibited 1 μM tenofovir with a 50% inhibitory concentration (IC(50)) of 14.0 μM, and tenofovir inhibited 1 μM raltegravir with an IC(50) of 27.3 μM. Raltegravir concentrations were not altered by transporter inhibitors in peripheral blood mononuclear cells or primary renal cells. Raltegravir is a substrate for SLC22A6 and SLC15A1 in the oocyte expression system. However, transport was limited compared to endogenous controls, and these transporters are unlikely to have a great impact on raltegravir pharmacokinetics.

Clinical pharmacology profile of raltegravir, an HIV-1 integrase strand transfer inhibitor

Raltegravir is an HIV-1 integrase inhibitor approved to treat HIV infection in adults in combination with other antiretrovirals. Data from healthy volunteers demonstrate that raltegravir is rapidly absorbed with a mean half-life of approximately 7 to 12 hours, with steady state achieved in approximately 2 days. Raltegravir is characterized by both high intra- and interindividual variabilities, although neither gender, race, age, body mass index, food intake, nor renal or hepatic insufficiency has a clinically meaningful effect on raltegravir pharmacokinetics. Raltegravir lacks activity as a perpetrator of drug-drug interactions and demonstrates a low propensity to be subject to drug-drug interactions. Raltegravir is metabolized primarily by UGT1A1 and is not affected by P450 inhibitors or inducers. Inhibitors of UGT1A1 (eg, atazanavir) can increase plasma concentrations of raltegravir, although this increase has not been found to be clinically meaningful. Likewise, inducers of UGT1A1 (eg, rifampin) can reduce plasma concentrations of raltegravir, and the clinical significance of this reduction is being investigated in ongoing clinical studies. Raltegravir demonstrates favorable clinical pharmacology and a drug interaction profile that permits administration to a wide, demographically diverse patient population and coadministration with many other therapeutic agents, including antiretroviral agents and supportive medications, without restrictions or dose adjustment.

Lack of interaction between the HIV integrase inhibitor S/GSK1349572 and tenofovir in healthy subjects

BACKGROUND

The potential for a drug interaction between S/GSK1349572 and tenofovir disoproxil fumarate (TDF) was evaluated in an open-label, repeat dose, 3-period, drug-drug interaction study in healthy subjects.

METHODS

S/GSK1349572 was administered at 50 mg once daily for 5 days (period 1) followed by a 6-day washout period. TDF 300 mg once daily was then administered for 7 days (period 2). The combination of S/GSK1349572 and TDF was then coadministered for 5 days (period 3). Pharmacokinetic parameters were determined and compared between periods.

RESULTS

Fifteen subjects completed all periods and follow-up. S/GSK1349572 and TDF were generally well tolerated with few adverse events reported. No clinically significant trends in post-dose laboratory abnormalities, vital signs, or electrocardiogram values were noted. Pharmacokinetic parameters of S/GSK1349572 and tenofovir during combination therapy were similar to those when given alone, demonstrating no significant drug interaction. S/GSK1349572 geometric least squares mean ratios (90% confidence interval) for AUC(0-τ), Cmax, and Cτ were 1.01 (0.908, 1.11), 0.969 (0.867, 1.08), and 0.920 (0.816, 1.04), respectively. Tenofovir geometric least squares mean ratios (90% confidence interval) for AUC(0-τ), Cmax, and Cτ were 1.12 (1.01, 1.24), 1.09 (0.974, 1.23), and 1.19 (1.04, 1.35), respectively.

CONCLUSION

S/GSK1349572 and TDF can be coadministered without dose adjustment.

Pharmacokinetics of etravirine, raltegravir and darunavir/ritonavir in treatment experienced patients

Etravirine is an enzyme inducer and could lower the concentration of combined drugs. Ten HIV-1-infected patients with multiple treatment failure received raltegravir (400 mg, twice daily) and darunavir/ritonavir (600/100 mg, twice daily). Addition of etravirine (200 mg, twice daily) leads to a significant increase in raltegravir and darunavir trough concentrations (405 vs. 118 and 3837 vs. 2241 ng/ml) and darunavir area under the curve (AUC(12h)) (50 083 vs. 36 277 ng h/ml). All pharmacokinetic parameters appeared to be highly variable regardless to the addition of etravirine.

Raltegravir: The evidence of its therapeutic value in HIV-1 infection

Introduction:

The antiretroviral treatment paradigm for human immunodeficiency virus-1 (HIV-1) infection has undergone a significant change with the addition of a new class of therapeutic agents targeting HIV-1 integrase (IN). IN inhibitors prevent the integration of viral DNA into the human genome and terminate the viral life cycle. As the first member of this new class of anti-HIV drugs, raltegravir has shown promising results in the clinic.

Aims:

To review the emerging evidence for the use of the IN inhibitor raltegravir in the treatment of HIV-1 infection.

Evidence review:

Strong evidence shows that raltegravir is effective in reducing the viral load to less than 50 copies/mL and increasing CD4 cell count in treatment-experienced patients with triple-drug class-resistant HIV-1 infection. Substantial evidence also indicates that while raltegravir is able to achieve treatment response in patients with drug-resistant HIV-1, it is susceptible to development of resistance. Raltegravir should be used with at least one other active drug. In addition to its use in salvage therapy upon failure of first-line antiretroviral treatment, a raltegravir-based treatment regimen may also be effective as initial therapy. Substantial evidence also shows that raltegravir-based treatment regimen is well tolerated with minimal clinically severe adverse events and toxicities. Modeling studies suggest a cost-effectiveness of US$21,339 per quality-adjusted life year gained with raltegravir use, though further direct evidence on quality of life and cost-effectiveness is needed.

Place in therapy:

Raltegravir shows significant and sustained virologic and immunologic response in combination with other antiretrovirals in treatment-experienced HIV-1 infected patients who show evidence of viral replication or multidrug-resistant HIV-1 strains, without any significant tolerability issues.

Drug-drug interactions with raltegravir

Objective

To review all currently published drug-drug interaction studies with the HIV-integrase inhibitor raltegravir.

Methods

A PubMed search was conducted for all published reports up to August 1, 2009 as well as a review of updated European and US Prescriber's Information (EMEA & FDA) and abstracts from recent international scientific meetings.

Results

A total of 14 drug-drug interaction studies were found. Due to the relatively broad therapeutic range of raltegravir almost all co-administered agents can safely be combined with raltegravir, with the exception of rifampin in which a doubling of the raltegravir dose to 800 mg BD is currently recommended.

Conclusions

Raltegravir is not without drug-drug interactions but due to the lack of an effect on CYP450 or UGT by raltegravir and the broad therapeutic range of raltegravir itself, this agent can safely combined with almost all tested agents.

Implementation of raltegravir in routine clinical practice: selection criteria for choosing this drug, virologic response rates, and characteristics of failures

BACKGROUND

Raltegravir (RAL) achieved remarkable virologic suppression rates in randomized-clinical trials, but today efficacy data and factors for treatment failures in a routine clinical care setting are limited.

METHODS

First, factors associated with a switch to RAL were identified with a logistic regression including patients from the Swiss HIV Cohort Study with a history of 3 class failure (n = 423). Second, predictors for virologic outcome were identified in an intent-to-treat analysis including all patients who received RAL. Last observation carried forward imputation was used to determine week 24 response rate (HIV-1 RNA >or= 50 copies/mL).

RESULTS

The predominant factor associated with a switch to RAL in patients with suppressed baseline RNA was a regimen containing enfuvirtide [odds ratio 41.9 (95% confidence interval: 11.6-151.6)]. Efficacy analysis showed an overall response rate of 80.9% (152/188), whereas 71.8% (84/117) and 95.8% (68/71) showed viral suppression when stratified for detectable and undetectable RNA at baseline, respectively. Overall CD4 cell counts increased significantly by 42 cells/microL (P < 0.001). Characteristics of failures were a genotypic sensitivity score of the background regimen <or=1, very low RAL plasma concentrations, poor adherence, and high viral load at baseline.

CONCLUSIONS

Virologic suppression rates in our routine clinical care setting were promising and comparable with data from previously published randomized-controlled trials.

Integrase inhibitors: a novel class of antiretroviral agents

OBJECTIVE

To review the pharmacology, efficacy, safety, and resistance profiles of the integrase inhibitors raltegravir and elvitegravir.

DATA SOURCES

A search of PubMed was conducted (2000-August 2009) using the following key words: raltegravir, MK-0518, elvitegravir, and GS-9137. Articles were evaluated for content and bibliographies were reviewed. Data available exclusively in abstracts from major infectious diseases and HIV conferences were also evaluated for inclusion.

STUDY SELECTION AND DATA EXTRACTION

Studies included were in vitro investigations; Phase 1, 2, and 3 clinical trials; retrospective analyses including case reports; and pharmacokinetic and pharmacodynamic evaluations.

DATA SYNTHESIS

Raltegravir is currently approved by the Food and Drug Administration for the management of HIV-1 infection in treatment-naïve or-experienced adults as part of an optimized combination regimen. When combined with other active agents, it has demonstrated similar virologic efficacy after 96 weeks to the combination of efavirenz, tenofovir, and emtricitabine in treatment-naïve patients. Unlike many antiretrovirals, raltegravir does not enter cytochrome P450 metabolism and instead undergoes glucuronidation. Elvitegravir is in the late stages of clinical development. A Phase 2 study has demonstrated virologic efficacy in treatment-experienced patients comparable to protease inhibitor-based regimens after 24 weeks. Boosting of elvitegravir through inhibition of CYP3A4 metabolism has been investigated and suggests a pharmacokinetic profile conducive to once-daily-dosing. Phase 2 and 3 clinical trials evaluating boosted elvitegravir are in process. The Phase 2 trial combines elvitegravir with a non-ritonavir boosting agent plus tenofovir/emtricitabine given once daily as a "quad-pill" formulation. The Phase 3 trial compares once-daily ritonavir-boosted elvitegravir with twice-daily raltegravir, each given with an optimized background regimen. Both integrase inhibitors are well tolerated and raltegravir has few drug-drug interactions. Resistance mutations have been identified in patients experiencing virologic failure and cross resistance between raltegravir and elvitegravir has been confirmed.

CONCLUSIONS

The integrase inhibitors provide a novel target for antiretroviral therapy and provide an option for patients harboring resistance to other antiretrovirals.

Safety and efficacy of raltegravir-based versus efavirenz-based combination therapy in treatment-naive patients with HIV-1 infection: a multicentre, double-blind randomised controlled trial

BACKGROUND

Use of raltegravir with optimum background therapy is effective and well tolerated in treatment-experienced patients with multidrug-resistant HIV-1 infection. We compared the safety and efficacy of raltegravir with efavirenz as part of combination antiretroviral therapy for treatment-naive patients.

METHODS

Patients from 67 study centres on five continents were enrolled between Sept 14, 2006, and June 5, 2008. Eligible patients were infected with HIV-1, had viral RNA (vRNA) concentration of more than 5000 copies per mL, and no baseline resistance to efavirenz, tenofovir, or emtricitabine. Patients were randomly allocated by interactive voice response system in a 1:1 ratio (double-blind) to receive 400 mg oral raltegravir twice daily or 600 mg oral efavirenz once daily, in combination with tenofovir and emtricitabine. The primary efficacy endpoint was achievement of a vRNA concentration of less than 50 copies per mL at week 48. The primary analysis was per protocol. The margin of non-inferiority was 12%. This study is registered with ClinicalTrials.gov, number NCT00369941.

FINDINGS

566 patients were enrolled and randomly allocated to treatment, of whom 281 received raltegravir, 282 received efavirenz, and three were never treated. At baseline, 297 (53%) patients had more than 100 000 vRNA copies per mL and 267 (47%) had CD4 counts of 200 cells per microL or less. The main analysis (with non-completion counted as failure) showed that 86.1% (n=241 patients) of the raltegravir group and 81.9% (n=230) of the efavirenz group achieved the primary endpoint (difference 4.2%, 95% CI -1.9 to 10.3). The time to achieve such viral suppression was shorter for patients on raltegravir than on efavirenz (log-rank test p<0.0001). Significantly fewer drug-related clinical adverse events occurred in patients on raltegravir (n=124 [44.1%]) than those on efavirenz (n=217 [77.0%]; difference -32.8%, 95% CI -40.2 to -25.0, p<0.0001). Serious drug-related clinical adverse events occurred in less than 2% of patients in each drug group.

INTERPRETATION

Raltegravir-based combination treatment had rapid and potent antiretroviral activity, which was non-inferior to that of efavirenz at week 48. Raltegravir is a well tolerated alternative to efavirenz as part of a combination regimen against HIV-1 in treatment-naive patients.

FUNDING

Merck.

Pharmacokinetics and drug-drug interactions of antiretrovirals: an update

Current antiretroviral treatment has allowed HIV infection to become a chronic manageable condition with many HIV patients living longer. However, available antiretrovirals are not without limitations, for example the development of resistance and adverse effects. Consequently, new drugs in existing and novel classes are urgently required to provide viable treatment options to patients with few remaining choices. Darunavir, etravirine, maraviroc and raltegravir have been recently approved for treatment-experienced patients and other agents such as rilpivirine, vicriviroc and elvitegravir are currently under phase III study. Clinical studies are necessary to optimise potential treatment combinations and to manage drug-drug interactions to help avoid toxicity or therapy failure. This review aims to summarise the pharmacokinetics and key drug-drug interaction studies for newly available antiretrovirals and those in development. Further information regarding drug-drug interactions of well established antiretrovirals and those recently approved are readily available online at sites such as http://www.hiv-druginteractions.org, http://www.clinicaloptions.com/hiv, http://hivinsite.ucsf.edu. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

Emerging pharmacology: inhibitors of human immunodeficiency virus integration

The first integrase inhibitor licensed to treat HIV-1 infection was approved in late 2007, more than a decade after the introduction of the first inhibitors of the HIV-1 reverse transcriptase and protease. The unique biochemical and molecular mechanism of action of this novel class of antiretroviral drugs is the fundamental basis for their activity in treating multidrug-resistant HIV-1 infection and is important for understanding both the cellular and in vivo pharmacology and metabolism of these agents. In addition, available pharmacokinetic and drug interaction data for raltegravir and elvitegravir, the two integrase inhibitors that are the most advanced in clinical development to date, are reviewed.

Raltegravir: the first HIV integrase inhibitor

BACKGROUND

The availability of new classes of antiretroviral drugs has made it possible for HIV-infected individuals who are highly treatment experienced to achieve the goals of immunologic recovery and virologic suppression. Raltegravir is the first integrase inhibitor to be approved by the US Food and Drug Administration for use in antiretroviral treatment- experienced adult patients with viral resistance.

OBJECTIVE

This article reviews the pharmacology, pharmacokinetics, pharmacodynamics, efficacy, tolerability, resistance profile, drug interactions, and dosing and administration of raltegravir.

METHODS

Searches of MEDLINE and International Pharmaceutical Abstracts from 1964 to July 2008 were conducted using the terms integrase, raltegravir, and MK-0518. Relevant information was extracted from the identified clinical trials and review articles. Abstracts from the Conference on Retroviruses and Opportunistic Infections (1998-2008); Interscience Conference on Antimicrobial Agents and Chemotherapy (1999-2007); International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention (2001-2007); and European AIDS Conference (2001-2007) were also searched.

RESULTS

Raltegravir blocks HIV replication by inhibiting essential strand-transfer activities of integrase. Raltegravir is rapidly absorbed, with a median T(max) of approximately 4 hours in the fasting state. No dose adjustment is recommended in patients with moderate renal or hepatic insufficiency, and raltegravir may be taken without regard to meals. In Phase II studies in treatment-naive patients, raltegravir had efficacy similar to that of standard initial therapies. In 2 interrelated Phase III clinical studies in treatment-experienced patients with drug-resistant disease, the addition of raltegravir to an optimized background regimen significantly lowered HIV RNA compared with optimized background treatment alone (62.1% vs 32.9%, respectively; P < 0.001). Raltegravir was generally well tolerated. The most common adverse effects reported in Phase II/III trials in treatment-experienced patients were diarrhea (16.6%), nausea (9.9%), and headache (9.7%). Cytochrome P450-related drug interactions are not expected, as raltegravir is not a CYP substrate, inducer, or inhibitor. However, to prevent failure of raltegravir, the drug should not be coadministered with rifampin.

CONCLUSION

Raltegravir is a potent and generally well tolerated antiretroviral agent that may play an important role in the treatment of patients harboring resistance to other antiretrovirals.