Efficacy and safety of TMC125 (etravirine) in treatment-experienced HIV-1-infected patients in DUET-1: 24-week results from a randomised, double-blind, placebo-controlled trial

[Etravirine in first-line therapy]

Etravirine (ETR) is a non-nucleoside reverse transcriptase inhibitor (NNRTI) with a potent and broad in vitro spectrum of activity against HIV-1 and viruses with NNRTI resistances, allowing sequential use of drugs of this family. The potency, efficacy and safety of etravirine have been demonstrated in multi-treated patients, but few data are available on first-line antiretroviral therapy (ART) and the role of this drug in initial treatment phases has not been defined. The presence of primary NNRTI resistances and those acquired during first-line therapy is increasingly frequent. Due to its genetic barrier and efficacy, ETR can form part of a second-line ART regimen in patients with failure to a first-line regimen. In the initial phases, adverse effects continue to be the main reason for modifying ART. ETR has demonstrated safety and tolerability, with no central nervous system adverse effects and a good liver, lipid and gastrointestinal safety profile. As with the other NNRTIs, the most common adverse effect is rash. Because of ETR good tolerability profile, this drug can be considered when a new treatment is required due to adverse effects. Because of the characteristics of ETR the possibility of once-daily administration and dissolution in water, as well as the absence of drug-drug interactions with methadone this drug is especially attractive as a firstline therapy and in patients with poor adherence, such as intravenous drug users receiving methadone treatment.

[Chemical characteristics, mechanism of action and antiviral activity of etravirine]

Etravirine (ETR) is a diarylpyrimidine derivative with a polycyclic molecule composed of 3 aromatic rings with single bonds between the rings (C(20)H(15)BrN(60)). The drug acts through a mechanism of noncompetitive inhibition on binding to a hydrophobic binding pocket, very close to the active center of the enzyme, provoking an allosteric transition to a conformation that distorts its structure and impedes DNA polymerization. The 3 rings with single bonds between the rings confer the molecule with great fl exibility and torsion. Because of these characteristics, etravirine can adapt to conformational changes in the binding pocket, including a large number of the conformations provoked by the resistance mutations that appear after failure to regimens that include efavirenz or nevirapine. This specific chemical structure largely explains the drug's distinguishing features in terms of its antiviral potency and high genetic barrier. ETR is a highly active molecule against HIV-1. This drug has a high genetic barrier to resistance and has demonstrated antiviral activity against a wide panel of recombinant viruses that incorporate resistance mutations to first-generation non-nucleoside analogues. Equally, ETR has demonstrated efficacy against several subtypes of the M group of HIV-1 (A, B, C, D, F and H, and recombinant forms CRF01_AE, CRF02_AG, CRF05_DF), as well as against isolates of HIV-1 group O. ETR, as the rest of non-nucleoside analogues, does not have demonstrated antiviral activity against HIV-2.

[Etravirine: genetic barrier and resistance development]

Unlike first-generation non-nucleoside reverse transcriptase inhibitors (NNRTI), to develop complete resistance to etravirine (ETR), various mutations must be accumulated. This drug shows an intermediate barrier against partial resistance and a high barrier to complete resistance. Some mutations selected by nevirapine or efavirenz affect the activity of ETR, the most frequent being Y181C, G190A/S, K101E, L100I, Y188L and V90I. The grade of resistance conferred by each mutation differs. Currently, there are at least three lists of mutations that confer an exact score to each mutation. These lists have been validated with the grade of resistance observed in paired phenotypes and with clinical response in the DUET studies. The three scores show a high degree of agreement. ETR is currently one of the antiretroviral drugs whose activity can be calculated simply and accurately on the basis of genotypic data. The mutations selected after failure to nucleoside reverse transcriptase inhibitors, thymidine analogue, T69D/N and M184I/V, confer hypersusceptibility to ETR (fold change < 0.4) in up to 1 out of every 3 samples analyzed. The early withdrawal of first-generation NNRTIs in patients with virological failure is essential to avoid the accumulation of mutations that could compromise the activity of this drug.

Combination of V106I and V179D polymorphic mutations in human immunodeficiency virus type 1 reverse transcriptase confers resistance to efavirenz and nevirapine but not etravirine

Etravirine (ETV) is a second-generation nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) introduced recently for salvage antiretroviral treatment after the emergence of NNRTI-resistant human immunodeficiency virus type 1 (HIV-1). Following its introduction, two naturally occurring mutations in HIV-1 RT, V106I and V179D, were listed as ETV resistance-associated mutations. However, the effect of these mutations on the development of NNRTI resistance has not been analyzed yet. To select highly NNRTI-resistant HIV-1 in vitro, monoclonal HIV-1 strains harboring V106I and V179D (HIV-1(V106I) and HIV-1(V179D)) were propagated in the presence of increasing concentrations of efavirenz (EFV). Interestingly, V179D emerged in one of three selection experiments from HIV-1(V106I) and V106I emerged in two of three experiments from HIV-1(V179D). Analysis of recombinant HIV-1 clones showed that the combination of V106I and V179D conferred significant resistance to EFV and nevirapine (NVP) but not to ETV. Structural analysis indicated that ETV can overcome the repulsive interactions caused by the combination of V106I and V179D through fine-tuning of its binding module to RT facilitated by its plastic structure, whereas EFV and NVP cannot because of their rigid structures. Analysis of clinical isolates showed comparable drug susceptibilities, and the same combination of mutations was found in some database patients who experienced virologic NNRTI-based treatment failure. The combination of V106I and V179D is a newly identified NNRTI resistance pattern of mutations. The combination of polymorphic and minor resistance-associated mutations should be interpreted carefully.

Effectiveness of boosted protease inhibitor-based regimens in HIV type 1-infected patients who experienced virological failure with NNRTI-based antiretroviral therapy in a resource-limited setting

A number of patients have experienced treatment failure while receiving non-nucleoside reverse transcriptase inhibitor (NNRTI)-based antiretroviral therapy (ART), particularly in resource-limited countries. The need remains for clinical data on protease inhibitor (PI)-based regimens in these patients. A retrospective cohort study was conducted among HIV-1-infected patients who had failed NNRTI-based regimens, were naive to protease inhibitors (PIs), and subsequently initiated a salvage PI-based regimen between January 2004 and December 2006. The study period ended on 30 December 2007. One hundred and forty patients received a single-boosted PI +/- optimized background regimen (OBR) and 64 received double-boosted PIs. The median (IQR) duration of follow-up was 19 (13-29) months. The overall virological failure rate at 24 months was 15.2%. No statistically significant difference was detected between the two regimen groups (single-boosted PI +/- OBR 16.4% vs. double-boosted PIs 12.5%, log rank p = 0.818). At the end of the study, the median (IQR) change in CD4 cell counts for patients in the double-boosted PI group was higher than for patients in the single-boosted PI +/- OBR group [149 (53-322) vs. 105 (23-199), respectively, p = 0.012]. Patients receiving double-boosted PI regimens displayed a higher frequency of hypertriglyceridemia than those patients who received a single boosted PI +/- OBR (31% vs. 11%, respectively, p = 0.001). Boosted PI-based regimens showed acceptable virological outcomes among patients who had failed NNRTI-based ART. In the subgroup analysis, patients who received double-boosted PIs demonstrated a superior immunological response but not better virological outcomes compared to the single-boosted PI +/- OBR group.

Etravirine resistance associated mutations in HIV-infected patients failing efavirenz or nevirapine in the Spanish antiretroviral resistance database

The prevalence of etravirine resistance mutations was examined in genotypes derived from 1343 HIV-infected patients failing nevirapine or efavirenz in the resistance database of the Spanish AIDS Research Network (ResRIS). Overall, etravirine-resistant genotypes were recognized in 18.7% of patients, with no significant differences between failures under nevirapine or efavirenz. Thus, more than 80% patients with prior failure to nonnucleoside reverse transcriptase inhibitors could potentially benefit from etravirine rescue therapy.

N348I in HIV-1 reverse transcriptase decreases susceptibility to tenofovir and etravirine in combination with other resistance mutations

We previously demonstrated that N348I in HIV-1 reverse transcriptase confers zidovudine and nevirapine resistance. However, both of these inhibitors are currently infrequently used in developed countries, and the impact of N348I on newer reverse transcriptase inhibitors, such as tenofovir and etravirine, is unknown. In this study, we demonstrate that N348I alone confers no resistance to tenofovir and low-level resistance to etravirine. However, N348I significantly decreases tenofovir susceptibility when combined with thymidine analogue mutations and etravirine susceptibility when combined with Y181C.

Efficacy and safety of etravirine at week 96 in treatment-experienced HIV type-1-infected patients in the DUET-1 and DUET-2 trials

BACKGROUND

Durable efficacy and long-term safety of antiretroviral therapy are important goals in the management of treatment-experienced patients. The 96-week efficacy and safety of the non-nucleoside reverse transcriptase inhibitor (NNRTI) etravirine were evaluated in the Phase III DUET trials.

METHODS

HIV type-1-infected treatment-experienced adults with viral loads >5,000 copies/ml and NNRTI and protease inhibitor resistance were randomized to receive etravirine 200 mg or placebo, each twice daily and in combination with a background regimen of darunavir/ritonavir twice daily, nucleoside/nucleotide reverse transcriptase inhibitors and optional enfuvirtide. The primary end point was the proportion of patients with viral load <50 copies/ml (intent-to-treat analysis, time-to-loss of virological response algorithm) at week 24. Results from both trials were combined in the pre-specified pooled 96-week analysis.

RESULTS

In total, 599 patients received etravirine and 604 received placebo. At week 96, 57% of patients in the etravirine group versus 36% in the placebo group had a viral load <50 copies/ml (P<0.0001); 91% and 88% of patients, respectively, had maintained this response from week 48. Mean increases in CD4(+) T-cell count from baseline at week 96 were 128 cells/mm(3) with etravirine versus 86 cells/mm(3) with placebo (P<0.0001). With the exception of rash, which was reported more frequently with etravirine than placebo (21% versus 12%, respectively; P<0.0001), the safety and tolerability profile of etravirine was similar to placebo over the treatment period.

CONCLUSIONS

Etravirine, in combination with an antiretroviral background regimen, provided durable virological and immunological responses with no new safety concerns in treatment-experienced patients over 96 weeks in the DUET trials.

Cost effectiveness of darunavir/ritonavir 600/100 mg bid in protease inhibitor-experienced, HIV-1-infected adults in Belgium, Italy, Sweden and the UK

BACKGROUND

Two phase II trials (POWER 1 and 2) have demonstrated that darunavir co-administered with low-dose ritonavir (DRV/r) provides significant clinical benefit compared with control protease inhibitors (PIs) in highly treatment-experienced, HIV-1-infected adults, when co-administered with optimized background therapy (OBR).

OBJECTIVE

To determine whether DRV/r is cost effective compared with control PIs, from the perspective of Belgian, Italian, Swedish and UK reimbursement authorities, when used in treatment-experienced patients similar to those included in the POWER 1 and 2 trials.

METHODS

An existing Markov model containing health states defined by CD4 cell count ranges (> 500, 351-500, 201-350, 101-200, 51-100 and 0-50 cells/mm³) and death was adapted for use in four European healthcare settings. Baseline demographics, CD4 cell count distribution and antiretroviral drug usage reflected those reported in the POWER 1 and 2 trials. Virological/immunological response rates and matching transition probabilities over the patient's lifetime were based on results from the POWER trials and published data. After treatment failure, patients were assumed to switch to a tipranavir-containing regimen plus OBR. For each CD4 cell count range, utility values and HIV-related mortality rates were obtained from the published literature. National all-cause mortality data and published data on the increased risk of non HIV-related mortality in HIV-infected individuals were taken into account in the model. Data from observational studies conducted in each healthcare setting were used to determine resource-use patterns and costs associated with each CD4 cell count range. Unit costs were derived from official local sources; a lifetime horizon was taken and discount rates were selected based on local guidelines.

RESULTS

In the base-case analysis, quality-adjusted life-year (QALY) gains of up to 1.397 in Belgium, over 1.171 in Italy, 1.142 in Sweden and 1.091 in the UK were predicted when DRV/r-based therapy was used instead of control PI-based treatment. The base-case analyses predicted an incremental cost-effectiveness ratio (ICER) of €11,438/QALY in Belgium, €12,122/QALY in Italy,€10,942/QALY in Sweden and €16,438/QALY in the UK. Assuming an acceptability threshold of €30,000/QALY, DRV/r-based therapy remained cost effective over all parameter ranges tested in extensive one-way sensitivity analyses. Probabilistic sensitivity analysis revealed a 95% (Belgium), 97% (Italy), 92% (Sweden) or 78% (UK) probability of attaining an ICER below this threshold.

CONCLUSION

From four European payer perspectives, DRV/r-based antiretroviral therapy is predicted to be cost effective compared with currently available control PIs, when both are used with an OBR in treatment-experienced, HIV-1-infected adults who failed to respond to more than one PI-containing regimen.

Role of etravirine in the management of treatment-experienced patients with human immunodeficiency virus type 1

Etravirine is an oral diarylpyrimidine compound, a second-generation human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase inhibitor (NNRTI) with expanded antiviral activity against NNRTI-resistant HIV-1, to be used in combination therapy for treatment-experienced patients. Compared with first-generation NNRTIs, etravirine has a high genetic barrier to resistance, and is better tolerated without the neuropsychiatric and hepatic side effects of efavirenz and nevirapine, respectively. Its safety profile is comparable to placebo with the exception of rash, which has been mild and self-limited in the great majority of patients. In phase III clinical trials among treatment-experienced patients harboring NNRTI-resistant HIV-1, etravirine in combination with an optimized background regimen (OBR) that included ritonavir-boosted darunavir demonstrated superior antiviral activity than the control OBR. In addition, patients on the etravirine arm had fewer AIDS-defining conditions, hospitalizations, and lower mortality compared with the OBR control arm.

Cost effectiveness of darunavir/ritonavir in highly treatment-experienced, HIV-1-infected adults in the USA

INTRODUCTION

Darunavir is a new protease inhibitor (PI) that is co-administered with low-dose ritonavir and has demonstrated substantial efficacy in clinical trials of highly treatment-experienced patients when combined with an optimized background regimen (with or without enfuvirtide). This study estimates the cost effectiveness of darunavir with ritonavir (DRV/r) in this population over 5-year and lifetime time horizons in the USA.

METHODS

A Markov model was used to follow a treatment-experienced HIV-1 cohort through six health states, based on CD4 cell count: greater than 500, 351-500, 201-350, 101-200, 51-100 and 0-50 cells/mm³, and death. The magnitude of the CD4 cell count increase and duration of increasing and stable periods were derived from week 48 DRV/r clinical trial results (POWER 1 and 2). The treatment pathway assumed one regimen switch following treatment failure on the initial regimen. The use of antiretroviral drugs was based on usage in DRV/r clinical trials. US daily wholesale acquisition costs were calculated using the recommended daily doses. For each CD4 cell count range, utility values, HIV-1-related mortality rates and costs for medical resources (other than antiretroviral drug costs) were obtained from published literature. Non-HIV-1-related mortality rates were calculated by applying a relative risk value to the US general population age and gender-specific mortality rates. Costs and outcomes were discounted at 3% per year. One-way and probabilistic sensitivity analyses and variability analysis were performed.

RESULTS

In a 5-year analysis, patients receiving DRV/r experienced 3.80 quality-adjusted life-years (QALYs) and incurred total medical costs of US$217,288, while those receiving control PIs experienced 3.60 QALYs and incurred costs of US$218,962. DRV/r was both more effective and less costly than control PIs. For the lifetime analysis, the QALYs and lifetime medical costs with DRV/r were 10.03 and US$565,358, compared with 8.76 and US$527,287 with control PIs. The incremental cost-effectiveness ratio for DRV/r compared with control PIs was US$30,046. One-way sensitivity analyses for both time horizons indicated that the results were most sensitive to changes in the rate of CD4 cell count change during stable and declining periods (lifetime only), duration of stable period (5-year only) and HIV-1-related mortality rates. The results of the variability analysis were most sensitive to the model time horizon. Nevertheless, for all ranges and scenarios tested in these analyses, the incremental cost per QALY gained remained below US$50,000. The probabilistic sensitivity analysis showed that there was a 0.921 and 0.950 probability of a cost-effectiveness ratio below US$50,000 per QALY for the 5-year and lifetime time horizon, respectively.

CONCLUSIONS

DRV/r is predicted to be cost effective compared with control PI in highly treatment-experienced patients and is predicted to yield an average of 0.20 additional QALYs per treatment-experienced patient over 5 years and 1.27 additional QALYs over a lifetime in this population.

The cost of managing HIV infection in highly treatment-experienced, HIV-infected adults in France

BACKGROUND

Highly active antiretroviral therapy (HAART) has greatly enhanced HIV management, lowering the risk of clinical disease progression and death by substantially improving HIV-induced immune deficiency. Lower CD4 cell counts have consistently been associated with higher direct costs of HIV patient care. The aim of this study was to analyze HIV costs of care in France at different levels of HIV-induced immune deficiency (as measured by the CD4 cell count) using recent data from treatment-experienced patients.

METHODS

This analysis used data from the French Hospital Database in HIV, containing data on approximately 50% of the French HIV population. Patients were included in the analysis if they had visited a participating centre from 2003 to 2005, had CD4 cell counts determined at least twice during the study period, and had been prescribed at least two nucleoside reverse transcriptase inhibitors, one non-nucleoside reverse transcriptase inhibitor and two protease inhibitors since their first consultation. Resources consumed were counted and aggregated according to the CD4 cell count level. Standard costs were applied.

RESULTS

Periods with the lowest CD4 cell counts were associated with increased prescription rates of antiviral agents (other than anti-HIV agents), antiparasitic drugs and antimycobacterial agents. Antiretroviral treatments accounted for 80% of all medications prescribed during the study period. Hospitalization rates decreased with increasing CD4 cell counts, with 0.72 hospitalizations per patient-year for those with CD4 cell counts of 50 cells/mm³ or less compared with 0.05 per patient-year for patients with CD4 cell counts greater than 500 cells/mm³. There was a clear trend towards lower mean healthcare costs per patient-year with decreasing immune deficiency; from €34,286 to €12,361.

CONCLUSIONS

Our study showed an association between the degree of HIV-induced immune deficiency (measured by CD4 cell count) and the costs of managing HIV infection among highly pre-treated, HIV-infected individuals in France in the HAART era.

Antiretroviral medications: adverse effects on the kidney

The widespread introduction of highly active antiretroviral therapy (HAART) in the mid-1990s dramatically altered the course of human immunodeficiency virus (HIV) infection, with improvements in survival and reductions in the incidence of AIDS-defining illnesses. Although antiretroviral therapy has been shown to reduce the incidence of both AIDS-defining and non-AIDS conditions, long-term exposure to HAART may also be associated with significant toxicity. This article reviews the potential nephrotoxicity of specific antiretroviral agents and the impact of antiretroviral therapy on related metabolic disorders. The antiretroviral agents most strongly associated with direct nephrotoxicity include the nucleotide reverse transcriptase inhibitor, tenofovir, and the protease inhibitor indinavir, although other agents have been implicated less frequently. Tenofovir and related nucleotide analogs have primarily been associated with proximal tubular dysfunction and acute kidney injury, whereas indinavir is known to cause nephrolithiasis, obstructive nephropathy, and interstitial nephritis. Kidney damage related to antiretroviral therapy is typically reversible with early recognition and timely discontinuation of the offending agent, and nephrologists should be familiar with the potential toxicity of these agents to avoid delays in diagnosis.

Combining protease inhibitors with new drug classes in treatment-experienced patients

PURPOSE OF REVIEW

The availability of new drugs in existing classes and new drugs in new classes has enabled better management of the treatment-experienced patient. This review will highlight the advances in the field and the new goals of therapy for this patient population.

RECENT FINDINGS

The treatment-experienced patient on a failing regimen should receive a new combination of at least two, and ideally three, new agents that includes a drug within a new class. The goal of therapy is suppression of viral replication to less than 50 copies/ml. The new protease inhibitors with activity against strains with resistance to earlier members of the class are an important backbone to the new therapy given their high barrier to resistance.

SUMMARY

The treatment-experienced patient can now be successfully managed with new agents and new classes of antiviral agents.

Pharmacologic characteristics of investigational and recently approved agents for the treatment of HIV

PURPOSE OF REVIEW

Two agents from antiretroviral classes with novel mechanisms of action against HIV received regulatory approval in 2007. Maraviroc is the first in the class of chemokine coreceptor 5 antagonists and raltegravir is the first in the class of integrase inhibitors. There are other compounds in these two new classes in later stages of clinical development, as well as several protease inhibitors and nonnucleoside reverse transcriptase inhibitors that have been recently approved or are under investigation for use in treatment-experienced patients. The purpose of this article is to review the pharmacologic characteristics of these newly approved and investigational antiretroviral drugs, with particular emphasis on data presented or published within the past year.

RECENT FINDINGS

Several pivotal studies describing the efficacy, safety, and pharmacologic properties of maraviroc, vicriviroc, etravirine, rilpivirine, raltegravir, elvitegravir, darunavir/ritonavir, and tipranavir/ritonavir have begun to emerge.

SUMMARY

To date, these agents have demonstrated promising virologic activity with primarily excellent tolerability, but there is still much to learn about their pharmacology. Future studies should evaluate their potential for drug-drug interactions and elucidate their concentration-effect relationships. An appreciation for the pharmacology of these drugs is critical to their optimal use.

Regulatory issues in developing new HIV protease inhibitors: risks and benefits

PURPOSE OF REVIEW

To provide a regulatory perspective on developing new HIV protease inhibitors. The present review highlights the risks and benefits of certain design aspects for studies in treatment-naïve and treatment-experienced patients, including timing of studies, study design options, choice of control arms, and duration of treatment.

RECENT FINDINGS

The present review highlights published studies to illustrate the need for new therapies and highlights potential historical data to help design future HIV clinical trials better.

SUMMARY

New antiretroviral agents for patients with multidrug resistance, including safer, more convenient therapies without significant drug-drug interactions, are still needed for all patients. The goals of therapy have evolved and the expectation for treatment regimens is that the majority of patients, including treatment-experienced patients, will achieve undetectable HIV RNA. New study designs, particularly for treatment-experienced patients, are needed to help identify potential risks and benefits of new treatments.

Resistance-associated mutations to etravirine (TMC-125) in antiretroviral-naïve patients infected with non-B HIV-1 subtypes

Susceptibility to etravirine (ETR), an expanded-spectrum nonnucleoside reverse transcriptase inhibitor (NNRTI), is dependent on the type and number of NNRTI resistance-associated mutations (RAMs). Studies have shown that some HIV-1 subtypes may have natural polymorphisms described as ETR RAMs. This study addresses the prevalence of ETR RAMs in treatment-naïve patients infected with HIV-1 non-B subtypes and its potential impact on ETR susceptibility. The prevalence of ETR RAMs in 726 antiretroviral-naïve patients infected with non-B HIV-1 subtypes was studied. ETR genotypic resistance was interpreted according to Agence Nationale de Recherches sur le SIDA and Stanford algorithms. NNRTI phenotypic susceptibilities of samples with at least one ETR RAM were measured. Overall, 75 (10.3%) of 726 sequences harbored at least one ETR RAM: sequences from 72 patients (10%) each had one ETR RAM, and sequences from 3 patients (0.4%) each had two ETR RAMs (V90I and Y181C in one case and V90I and A98G in two cases). None of the viruses had three or more ETR RAMs, and none were consequently classified as resistant to ETR. All sequences with two ETR RAMs belonged to subtype CRF02_AG. The presence of one ETR RAM was statistically more frequent in subtype CRF02_AG than in other non-B subtypes (P=0.004). Three new mutation profiles (E138A and V179I, Y181C and H221Y, and V90I and Y181C) showing decreased ETR phenotypic susceptibility were identified. In conclusion, although the prevalence of ETR RAMs in treatment-naïve patients infected with non-B HIV-1 subtypes was 10%, in most cases this had no significant impact on ETR susceptibility. However, the transmission of drug-resistant viruses with Y181C in a non-B genetic background has a potential for impact on ETR susceptibility.

Nonnucleoside reverse transcriptase inhibitor resistance and the role of the second-generation agents

OBJECTIVE

To review the current state of nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance, discuss the promising role of second-generation NNRTIs, and provide insight into their clinical utility.

DATA SOURCES

Articles were identified through searches of MEDLINE (May 2000-August 2009) and International Pharmaceutical Abstracts (May 1998-August 2009), using the key words etravirine, rilpivirine, TMC125, TMC278, diarylpyrimidine, NNRTI, and resistance.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials, resistance studies, and pharmacokinetic data were selected for review.

DATA SYNTHESIS

NNRTIs are an integral class of antiretroviral agents utilized for the treatment of HIV-1 infection. These agents have become preferred therapy options for treatment-naïve individuals per treatment guideline recommendations and have gained increased popularity over protease inhibitor-based antiretroviral therapy. However, available NNRTIs possess inherent characteristics, such as low genetic barrier to resistance and high degree of cross-resistance, that limit their use in HIV therapy. Due to the growing utilization of this highly efficacious antiretroviral class and the increased capability for resistance development, many HIV-infected patients have experienced treatment failure of an NNRTI. Cross-resistance makes other first-generation NNRTI agents unavailable for future use. Etravirine and rilpivirine are second-generation NNRTIs that are not significantly hampered by cross-resistance and possess potent antiretroviral activity against current NNRTI-resistant viral strains. These agents provide new and important therapy options for many HIV-infected patients.

CONCLUSIONS

NNRTI resistance is an increasing problem that may impair the chances for therapeutic success in HIV-infected patients. Novel agents such as etravirine and rilpivirine provide new, sensitive options for patients and significantly improve the rate of virologic suppression when appropriately applied.

Virologic and immunologic activity of PegIntron in HIV disease

OBJECTIVE

The primary objectives of this study were to evaluate the safety, tolerability, and antiviral activity of pegylated interferon-alpha (PegIntron) in HIV-1 treatment-experienced patients failing their current antiretroviral regimen.

DESIGN

This was a phase II, multicenter, randomized, double-blind, placebo-controlled study.

METHODS

Patients were randomized to receive either weekly subcutaneous PegIntron 0.5, 1.0, 1.5, or 3 microg/kg or placebo added to their failing antiretroviral regimen for the first 4 weeks of study. Individuals who achieved more than 0.5 log10 reduction in HIV RNA at week 4 were allowed to continue study medication with optimization of their antiretroviral therapy for an additional 24 weeks.

RESULTS

In the 259 patients included in the intent-to-treat analysis, changes in plasma HIV RNA from baseline to week 4 were -0.25 (P > 0.5), -0.46 (P = 0.024), -0.39 (P = 0.008), -0.53 (P < 0.001), and -0.17 (P > 0.5) log10 copies/ml in the 0.5, 1.0, 1.5, and 3.0 microg/kg and placebo arms, respectively. No significant changes were seen in CD4 T-cell parameters in any of the treatment or control arms. Adverse events (most commonly fever, flu-like symptoms, other constitutional symptoms, and psychiatric symptoms) resulted in discontinuation of study medication in 13, 17, 16, 28, and 2% of patients in the 0.5, 1.0, 1.5, 3.0 microg/kg, and placebo group, respectively.

CONCLUSION

The demonstration of significant antiviral activity in a heavily pretreated patient population with acceptable toxicity and only weekly dosing makes PegIntron a potentially valuable therapy for patients with HIV infection that warrants further investigation in a broader population of patients.

TMC278, a next-generation nonnucleoside reverse transcriptase inhibitor (NNRTI), active against wild-type and NNRTI-resistant HIV-1

Nonnucleoside reverse transcriptase inhibitors (NNRTIs) have proven efficacy against human immunodeficiency virus type 1 (HIV-1). However, in the setting of incomplete viral suppression, efavirenz and nevirapine select for resistant viruses. The diarylpyrimidine etravirine has demonstrated durable efficacy for patients infected with NNRTI-resistant HIV-1. A screening strategy used to test NNRTI candidates from the same series as etravirine identified TMC278 (rilpivirine). TMC278 is an NNRTI showing subnanomolar 50% effective concentrations (EC50 values) against wild-type HIV-1 group M isolates (0.07 to 1.01 nM) and nanomolar EC50 values against group O isolates (2.88 to 8.45 nM). Sensitivity to TMC278 was not affected by the presence of most single NNRTI resistance-associated mutations (RAMs), including those at positions 100, 103, 106, 138, 179, 188, 190, 221, 230, and 236. The HIV-1 site-directed mutant with Y181C was sensitive to TMC278, whereas that with K101P or Y181I/V was resistant. In vitro, considerable cross-resistance between TMC278 and etravirine was observed. Sensitivity to TMC278 was observed for 62% of efavirenz- and/or nevirapine-resistant HIV-1 recombinant clinical isolates. TMC278 inhibited viral replication at concentrations at which first-generation NNRTIs could not suppress replication. The rates of selection of TMC278-resistant strains were comparable among HIV-1 group M subtypes. NNRTI RAMs emerging in HIV-1 under selective pressure from TMC278 included combinations of V90I, L100I, K101E, V106A/I, V108I, E138G/K/Q/R, V179F/I, Y181C/I, V189I, G190E, H221Y, F227C, and M230I/L. E138R was identified as a new NNRTI RAM. These in vitro analyses demonstrate that TMC278 is a potent next-generation NNRTI, with a high genetic barrier to resistance development.

Raltegravir, etravirine, and ritonavir-boosted darunavir: a safe and successful rescue regimen for multidrug-resistant HIV-1 infection

BACKGROUND

Boosted darunavir (DRV/r) plus etravirine (ETR), in DUET trials, and raltegravir, in BENCHMRK trials, showed high rates of virologic response in patients with multidrug-resistant HIV-1 infection, particularly when associated with two more fully active antiretroviral drugs. No data from clinical trials, about this combination, are available.

PATIENTS AND METHODS

Thirty-two consecutive heavily pretreated patients with multidrug-resistant HIV-1 infection who started a new salvage regimen with RAL (400 mg twice daily), ETR (200 mg twice daily), and DRV/r (600/100 mg twice daily) were studied. Clinical evaluation and immunologic, virologic, and biochemical parameters were collected at baseline and at Weeks 4, 12, and 24.

RESULTS

Median baseline characteristics were age 44 years, 13 years on antiretroviral therapy, nine prior highly active antiretroviral therapy regimens, 261 CD4 cells/mL, and HIV-1 RNA 4.2 log10 copies/mL. Sixteen (50%) and 14 (44%) patients were enfuvirtide- and tipranavir-experienced, respectively. Three-class resistance mutations were present in all patients. Three patients (9%) had isolates with three ETR resistance mutations. All patients were DRV-naïve with a median of one DRV resistance mutation. At Weeks 4, 12, and 24, respectively, 63%, 81%, and 94% of patients achieved HIV1-RNA less than 50 copies/mL. Median CD4 cell count increased 30, 73, and 103 cells/mL at Weeks 4, 12, and 24, respectively. No patient had adverse events leading to discontinuation of the regimen.

CONCLUSION

The combination of raltegravir, ETR, and DRV/r was a highly effective and well-tolerated antiretroviral salvage regimen in patients infected with multidrug-resistant HIV-1.

Strand transfer inhibitors of HIV-1 integrase: bringing IN a new era of antiretroviral therapy

HIV-1 integrase (IN) is one of three essential enzymes (along with reverse transcriptase and protease) encoded by the viral pol gene. IN mediates two critical reactions during viral replication; firstly 3'-end processing (3'EP) of the double-stranded viral DNA ends and then strand transfer (STF) which joins the viral DNA to the host chromosomal DNA forming a functional integrated proviral DNA. IN is a 288 amino acid protein containing three functional domains, the N-terminal domain (NTD), catalytic core domain (CCD) and the C-terminal domain (CTD). The CCD contains three conserved catalytic residues, Asp64, Asp116 and Glu152, which coordinate divalent metal ions essential for the STF reaction. Intensive research over the last two decades has led to the discovery and development of small molecule inhibitors of the IN STF reaction (INSTIs). INSTIs are catalytic inhibitors of IN, and act to chelate the divalent metal ions in the CCD. One INSTI, raltegravir (RAL, Merck Inc.) was approved in late 2007 for the treatment of HIV-1 infection in patients with prior antiretroviral (ARV) treatment experience and was recently approved also for first line therapy. A second INSTI, elvitegravir (EVG, Gilead Sciences, Inc.) is currently undergoing phase 3 studies in ARV treatment-experienced patients and phase 2 studies in ARV naïve patients as part of a novel fixed dose combination. Several additional INSTIs are in early stage clinical development. This review will discuss the discovery and development of this novel class of antiretrovirals. 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.

Raltegravir, etravirine and r-darunavir combination in adolescents with multidrug-resistant virus

Twelve heavily pretreated, perinatally infected adolescents in virological failure were treated with a combination of raltegravir, r-darunavir and etravirine, as part of an expanded access program in France. After a 12-month median follow-up, viral load was <400 copies/ml in 11 (<50 in six). No grade > 2 side effects were recorded. Additional data and marketing authorizations are awaited, but preliminary results in adolescents with extensive multidrug resistant virus are encouraging.

Efficacy and safety of etravirine in treatment-experienced, HIV-1 patients: pooled 48 week analysis of two randomized, controlled trials

OBJECTIVE

To evaluate the efficacy, safety and virologic resistance profile of etravirine (TMC125), a next-generation nonnucleoside reverse transcriptase inhibitor, over 48 weeks in treatment-experienced adults infected with HIV-1 strains resistant to a nonnucleoside reverse transcriptase inhibitor and other antiretrovirals.

DESIGN

DUET-1 (NCT00254046) and DUET-2 (NCT00255099) are two identically designed, randomized, double-blind phase III trials.

METHODS

Patients received twice-daily etravirine 200 mg or placebo, each plus a background regimen of darunavir/ritonavir, investigator-selected nucleoside/nucleotide reverse transcriptase inhibitors and optional enfuvirtide. Eligible patients had documented nonnucleoside reverse transcriptase inhibitor resistance, at least three primary protease inhibitor mutations at screening and were on a stable but virologically failing regimen for at least 8 weeks, with plasma viral load more than 5000 copies/ml. Pooled 48-week data from the two trials are presented.

RESULTS

Patients (1203) were randomized and treated (n = 599, etravirine; n = 604, placebo). Significantly more patients in the etravirine than in the placebo group achieved viral load less than 50 copies/ml at week 48 (61 vs. 40%, respectively; P < 0.0001). Significantly fewer patients in the etravirine group experienced at least one confirmed or probable AIDS-defining illness/death (6 vs. 10%; P = 0.0408). Safety and tolerability in the etravirine group was comparable to the placebo group. Rash was the only adverse event to occur at a significantly higher incidence in the etravirine group (19 vs. 11%, respectively, P < 0.0001), occurring primarily in the second week of treatment.

CONCLUSION

At 48 weeks, treatment-experienced patients receiving etravirine plus background regimen had statistically superior and durable virologic responses (viral load less than 50 copies/ml) than those receiving placebo plus background regimen, with comparable tolerability and no new safety signals reported since week 24.

Factors associated with virological response to etravirine in nonnucleoside reverse transcriptase inhibitor-experienced HIV-1-infected patients

To identify factors associated with virological response (VR) to an etravirine (ETR)-based regimen, 243 patients previously treated with nonnucleoside reverse transcriptase inhibitors (NNRTIs) were studied. The impact of baseline HIV-1 RNA, CD4 cell count, past NNRTIs used, 57 NNRTI resistance mutations, genotypic sensitivity score (GSS) for nucleoside reverse transcriptase inhibitors (NRTIs) and protease inhibitors (PIs), and the number of new drugs used with ETR for the first time on the VR to an ETR regimen were investigated. Among the 243 patients, the median baseline HIV-1 RNA level was 4.4 log(10) copies/ml (interquartile range [IQR], 3.7 to 4.9) and the median CD4 count was 175 cells/mm(3) (IQR, 69 to 312). Patients had been previously exposed to a median of 6 NRTIs, 1, NNRTI, and 5 PIs. Overall, 82% of patients achieved a VR at month 2, as defined by a decrease of at least 1.5 log(10) copies/ml and/or HIV-1 RNA level of <50 copies/ml. No difference in VR was observed between patients receiving or not a boosted PI in combination with ETR. Factors independently associated with a better VR to ETR were the number of drugs (among enfuvirtide, darunavir, or raltegravir) used for the first time in combination with ETR and the presence of the K103N mutation at baseline. Mutations Y181V and E138A were independently associated with poor VR, whereas no effect of the Y181C on VR was observed. In conclusion, ETR was associated with high response rates in NNRTI-experienced patients in combination with other active drugs regardless of the therapeutic class used.

Efavirenz: a decade of clinical experience in the treatment of HIV

Efavirenz, a non-nucleoside reverse transcriptase inhibitor, has been an important component of the treatment of HIV infection for 10 years and has contributed significantly to the evolution of highly active antiretroviral therapy (HAART). The efficacy of efavirenz has been established in numerous randomized trials and observational studies in HAART-naive patients, including those with advanced infection. In the ACTG A5142 study, efavirenz showed greater virological efficacy than the boosted protease inhibitor (PI), lopinavir. Efavirenz is more effective as a third agent than unboosted PIs or the nucleoside analogue abacavir. Some, but not all, studies have suggested that efavirenz (added to two nucleoside reverse transcriptase inhibitors) is more effective than nevirapine. Virological and immunological responses achieved with efavirenz-based HAART have been maintained for 7 years. Dosing convenience predicts adherence, and studies have demonstrated that patients can be switched from PI-based therapy to simplified, once-daily efavirenz-based regimens without losing virological control. The one-pill, once-daily formulation of efavirenz plus tenofovir and emtricitabine offers a particular advantage in this regard. Efavirenz also retains a role after failure of a first PI-based regimen. Efavirenz is generally well tolerated: rash and neuropsychiatric disturbances are the most notable adverse events. Neuropsychiatric disturbances generally develop early in treatment and they tend to resolve with continued administration, but they are persistent and troubling in a minority of patients. Efavirenz has less effect on plasma lipid profiles than some boosted PIs. Lipodystrophy can occur under treatment with efavirenz but it may be reduced if the concurrent use of thymidine analogues is avoided. Efavirenz resistance mutations (especially K103N) can be selected during long-term treatment, underscoring the importance of good adherence. Recent data have confirmed that efavirenz is a cost-effective option for first-line HAART. In light of these features, efavirenz retains a key role in HIV treatment strategies and is the first-line agent recommended in some guidelines.

Understanding and managing the adverse effects of antiretroviral therapy

Highly active antiretroviral therapy (HAART) has changed the landscape of HIV disease in a way that seemed unthinkable a decade ago; from an almost uniformly fatal disease to a chronic manageable one. The first HAART regimens worked in suppressing virus, but were encumbered by a variety of short term and long term side effects. More recent regimens became simpler, easier to take, and with fewer adverse events. As we look to people living perhaps a normal life span with HIV, the increasing number of antiretroviral agents available means that individualizing treatment has become more feasible and the longer downstream adverse events related to HAART, such as its effect on cardiovascular disease and diabetes, renal and hepatic disease, have begun to dominate our choice of drugs. A knowledge of both the short and long term adverse events associated with HAART is essential for providers and for patients. For new drugs to be acceptable in the current field, they will have to pass a litmus test of tolerability. Since adverse events are often remarkably idiosyncratic, pharmacogenomics may offer a way of predicting side effects and their severity from a particular drug or drug class in individual patients. 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.

Etravirine for HIV-I: Addressing the Limitations of the Nonnucleoside Reverse Transcriptase Inhibitor Class

Etravirine (ETR) is a second-generation nonnucleoside reverse transcriptase inhibitor (NNRTI) specifically designed for treatment-experienced patients infected with HIV-1. Its unique strength over other, older agents in the NNRTI class is its higher genetic barrier to resistance, allowing it to be used effectively in patients with limited treatment options. The arrival of ETR in the market has made sequential NNRTI therapy possible for the first time in the history of HIV treatment, as it can maintain virologic activity in the presence of certain (and sometimes multiple) NNRTI mutations. Although ETR has demonstrated efficacy in treatment-experienced and NNRTI-resistant patients in large trials, further analyses on its resistance profile are ongoing. As new data emerge on the weighting of ETR’s resistance-associated mutations (RAMs), investigators and clinicians will no doubt be able to further characterize its specific place in the HIV treatment armamentarium.

Recent Advances in Pharmacotherapy

Many unique and clinically important medications were approved by the Food and Drug Administration from December 2007 through May 2008 for various conditions encountered in an internal medicine setting. These new treatments dramatically vary in their targeted body system and include agents for the cardiovascular system (nebivolol), central nervous system (desvenlafaxine), gastrointestinal tract (certolizumab, methylnaltrexone, and alvimopan), immunological function (etravirine), and metabolic function (sapropterin). This article discusses medications by their respective body system. Each review is comprised of an overview of the Food and Drug Administration–approved indication and the drug’s role in treatment of that disease state. Current dosing guidance, clinical efficacy and clinically relevant adverse drug reactions, drug interactions, contraindications, and precautions are also presented. This review is designed to focus on the new molecular entities and biological approvals clinicians may potentially encounter in an internal medicine practice.

HAART for children with treatment failure

Even as pediatric rollout programs are struggling to meet global need, increasing numbers of children are failing first-line antiretroviral therapy in low- and middle-income countries. Without better access to viral load monitoring, second-line antiretrovirals and research to guide optimal regimen selection, it will be difficult to ensure that HIV-infected children will survive into adulthood. Data available on pediatric drug resistance demonstrate that failure occurs early in childhood. Studies of salvage drug options have been promising, but are primarily conducted in adults. Evidence-based approaches to regimen selection, pediatric antiretroviral formulations and expanded access to novel drugs are now required to prepare for the future.

Running a tightrope: regulatory challenges in the development of antiretrovirals

Since the approval of Retrovir, (zidovudine, AZT) in 1987 by the Food and Drug Administration, a number of regulatory initiatives were codified into regulation which contributed to the rapid development of new treatments for HIV-1 infection. These initiatives are a testament to the efforts of AIDS activists and regulators to improve access to drugs for serious and life-threatening diseases. Currently, 28 antiretroviral drugs and combinations of antiretrovirals are available to treat HIV-1 infection. The broadening armamentarium of approved antiretroviral drugs provides new options and more choices for physicians and HIV patients. Importantly, the introduction of these newly approved HIV drugs has shown that the majority of HIV-1-infected treatment-naïve and treatment-experienced patients can achieve maximal virologic suppression (less than 50 copies/mL HIV-1 RNA). This article describes the past and current regulatory challenges in the development of new HIV treatments and provides an overview of the drug regulations that were required for the approval of HIV drugs. 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.

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.

Clinical cut-offs for HIV-1 phenotypic resistance estimates: update based on recent pivotal clinical trial data and a revised approach to viral mixtures

The clinical utility of HIV-1 resistance testing is dependent upon accurate interpretation and application of results. The development of clinical cut-offs (CCOs) for most HIV antiretroviral drugs assessed by the vircoTYPE HIV-1 resistance test has been described previously. Updated CCOs based on new methodology and new data from clinical cohorts and pivotal clinical studies are presented in this communication. Data for analysis included the original records for CCO derivation from eight clinical trials and two cohort studies plus new records from the clinical cohorts and from the TITAN, POWER, and DUET clinical studies. Drug-specific linear regression models were developed to describe the relationship between baseline characteristics (phenotypic resistance as estimated by virtualPhenotype-LM using methods revised recently for handling mixed viral sequences; viral load; and treatment history), new treatment regimen, and 8-week virologic outcome. The clinical cut-offs were defined as the estimated phenotypic resistance levels (fold change, FC) associated with a 20% and 80% loss of drug activity. The development dataset included 6550 records with an additional 2299 reserved for validation. The updated, v.4.2 CCOs were generally close to the v4.1 values, with a trend observed toward marginally higher cut-offs for the NRTIs. These results suggest that the updated CCOs provide a relevant tool for estimating the contribution to virological response of individual antiviral drugs in antiretroviral drug combinations as used currently in clinical practice.

Early virologic suppression with three-class experienced patients: 24-week effectiveness in the darunavir outcomes study

OBJECTIVE

To evaluate 24-week virologic effectiveness of novel antiretroviral regimens for treatment of three-class experienced adult patients in a clinical practice setting following the US Food and Drug Administration approval of darunavir (DRV) for this population.

DESIGN

A prospective cohort study.

SETTING

A single-center, academic HIV clinic.

PARTICIPANTS

Three-class antiretroviral-experienced patients changing regimens between July 2006 and May 2008. Sociodemographic, psychosocial, and clinical characteristics were collected at baseline and during prospective follow-up.

OUTCOME MEASURES

Plasma HIV viral load below 50 copies/ml and change in CD4 cell count at 24 weeks following regimen change. The Stanford Genotype Database was used to analyze HIV genotype resistance results and determine the number of active drugs in each regimen. Multivariate models and propensity score methods were employed to assess outcome measures.

RESULTS

Among 109 three-class experienced patients, who previously received an average of 10.5 prior antiretrovirals, 55% achieved viral load below 50 copies/ml at 24 weeks. Treatment strategy was classified as nonprotease inhibitor (n = 25), DRV/ritonavir (DRV/r) (n = 51), or other protease inhibitor (n = 33). The number of active drugs was not significantly different across strategies (P = 0.24). In multivariate analysis, patients treated with DRV/r (65%, odds ratio = 4.24 vs. nonprotease inhibitor strategy, 95% confidence interval = 1.28-14.06), raltegravir (65%, odds ratio = 3.10, 95% confidence interval = 1.12-8.62), or both were more likely to achieve viral load below 50 copies/ml.

CONCLUSION

Among antiretroviral-experienced patients changing regimens, those treated with DRV/r, raltegravir, or both were more likely to achieve a viral load below 50 copies/ml at 24 weeks. The effectiveness of these agents in routine clinical care mirrors their efficacy in clinical trials and has ushered in a new era in the therapy of three-class experienced patients.