Resistance profile of etravirine: combined analysis of baseline genotypic and phenotypic data from the randomized, controlled Phase III clinical studies

OBJECTIVE

To refine the genotypic and phenotypic correlates of response to the nonnucleoside reverse transcriptase inhibitor etravirine.

DESIGN

Initial analyses identified 13 etravirine resistance-associated mutations (RAMs) and clinical cutoffs (CCOs) for etravirine. A multivariate analysis was performed to refine the initial etravirine RAM list and improve the predictive value of genotypic resistance testing with regard to virologic response and relationship to phenotypic data.

METHODS

Week 24 data were pooled from the phase III studies with TMC125 to Demonstrate Undetectable viral load in patients Experienced with ARV Therapy (DUET). The effect of baseline resistance to etravirine on virologic response (<50 HIV-1 RNA copies/ml) was studied in patients not using de-novo enfuvirtide and excluding discontinuations for reasons other than virologic failure (n = 406). Clinical cutoffs for etravirine were established by analysis of covariance models and sliding fold change in 50% effective concentration (EC50) windows (Antivirogram; Virco BVBA, Mechelen, Belgium). Etravirine RAMs were identified as those associated with decreased virologic response/increased etravirine fold change in EC50. Relative weight factors were assigned to the etravirine RAMs using random forest and linear modeling techniques.

RESULTS

Baseline etravirine fold change in EC50 predicted virologic response at week 24, with lower and preliminary upper clinical cutoffs of 3.0 and 13.0, respectively. A fold change in EC50 value above which etravirine provided little or no additional efficacy benefit could not be established. Seventeen etravirine RAMs were identified and attributed a relative weight factor accounting for the differential impact on etravirine fold change in EC50. Virologic response was a function of etravirine-weighted genotypic score.

CONCLUSION

The weighted genotypic scoring algorithm optimizes resistance interpretations for etravirine and guides treatment decisions regarding its use in treatment-experienced patients.

[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.

Efficacy and safety of TMC278 in antiretroviral-naive HIV-1 patients: week 96 results of a phase IIb randomized trial

OBJECTIVE

TMC278 is a next-generation nonnucleoside reverse transcriptase inhibitor highly active against wild-type and nonnucleoside reverse transcriptase inhibitor-resistant HIV-1 in vitro. The week 96 analysis of TMC278-C204, a large dose-ranging study of TMC278 in treatment-naive HIV-1-infected patients, is presented.

DESIGN

Phase IIb randomized trial.

METHODS

Three hundred sixty-eight patients were randomized and treated with three blinded once-daily TMC278 doses 25, 75 or 150 mg, or an open-label, active control, efavirenz 600 mg once daily, all with two nucleoside reverse transcriptase inhibitors. The primary analysis was at week 48.

RESULTS

No TMC278 dose-response relationship for efficacy and safety was observed. TMC278 demonstrated potent antiviral efficacy comparable with efavirenz over 48 weeks that was sustained to week 96 (76.9-80.0% and 71.4-76.3% of TMC278-treated patients with confirmed viral load <50 copies/ml, respectively; time-to-loss of virological-response algorithm). Median increases from baseline in CD4 cell count with TMC278 at week 96 (138.0-149.0 cells/microl) were higher than at week 48 (108.0-123.0 cells/microl). All TMC278 doses were well tolerated. The incidences of the most commonly reported grade 2-4 adverse events at least possibly related to study medication, including nausea, dizziness, abnormal dreams/nightmare, dyspepsia, asthenia, rash, somnolence and vertigo, were low and lower with TMC278 than with efavirenz. Incidences of serious adverse events, grade 3 or 4 adverse events and discontinuations due to adverse events were similar among groups.

CONCLUSION

All TMC278 doses demonstrated potent and sustained efficacy comparable with efavirenz in treatment-naive patients over 96 weeks. TMC278 was well tolerated with lower incidences of neurological and psychiatric adverse events, rash and lower lipid elevations than those with efavirenz. TMC278 25 mg once daily was selected for further clinical development.

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.

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.

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.

Reverse transcriptase inhibitors as potential colorectal microbicides

We investigated whether reverse transcriptase (RT) inhibitors (RTI) can be combined to inhibit human immunodeficiency virus type 1 (HIV-1) infection of colorectal tissue ex vivo as part of a strategy to develop an effective rectal microbicide. The nucleotide RTI (NRTI) PMPA (tenofovir) and two nonnucleoside RTI (NNRTI), UC-781 and TMC120 (dapivirine), were evaluated. Each compound inhibited the replication of the HIV isolates tested in TZM-bl cells, peripheral blood mononuclear cells, and colorectal explants. Dual combinations of the three compounds, either NRTI-NNRTI or NNRTI-NNRTI combinations, were more active than any of the individual compounds in both cellular and tissue models. Combinations were key to inhibiting infection by NRTI- and NNRTI-resistant isolates in all models tested. Moreover, we found that the replication capacities of HIV-1 isolates in colorectal explants were affected by single point mutations in RT that confer resistance to RTI. These data demonstrate that colorectal explants can be used to screen compounds for potential efficacy as part of a combination microbicide and to determine the mucosal fitness of RTI-resistant isolates. These findings may have important implications for the rational design of effective rectal microbicides.

Antiviral activity of MK-4965, a novel nonnucleoside reverse transcriptase inhibitor

Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are the mainstays of therapy for the treatment of human immunodeficiency virus type 1 (HIV-1) infections. However, the effectiveness of NNRTIs can be hampered by the development of resistance mutations which confer cross-resistance to drugs in the same class. Extensive efforts have been made to identify new NNRTIs that can suppress the replication of the prevalent NNRTI-resistant viruses. MK-4965 is a novel NNRTI that possesses both diaryl ether and indazole moieties. The compound displays potency at subnanomolar concentrations against wild-type (WT), K103N, and Y181C reverse transcriptase (RT) in biochemical assays. MK-4965 is also highly potent against the WT virus and two most prevalent NNRTI-resistant viruses (viruses that harbor the K103N or the Y181C mutation), against which it had 95% effective concentrations (EC(95)s) of <30 nM in the presence of 10% fetal bovine serum. The antiviral EC(95) of MK-4965 was reduced approximately four- to sixfold when it was tested in 50% human serum. Moreover, MK-4965 was evaluated with a panel of 15 viruses with NNRTI resistance-associated mutations and showed a superior mutant profile to that of efavirenz but not to that of etravirine. MK-4965 was similarly effective against various HIV-1 subtypes and viruses containing nucleoside reverse transcriptase inhibitor or protease inhibitor resistance-conferring mutations. A two-drug combination study showed that the antiviral activity of MK-4965 was nonantagonistic with each of the 18 FDA-licensed drugs tested vice versa in the present study. Taken together, these in vitro data show that MK-4965 possesses the desired properties for further development as a new NNRTI for the treatment of HIV-1 infection.

Etravirine

Etravirine is a next-generation non-nucleoside reverse transcriptase inhibitor (NNRTI) that demonstrates potent in vitro activity against wild-type strains of HIV type 1 (HIV-1), as well as against numerous strains resistant to available NNRTIs. Furthermore, the potential for resistance to etravirine developing appears to be lower than for first-generation NNRTIs. In treatment-experienced patients infected with HIV-1 with NNRTI resistance, HIV-1 RNA levels of <50 copies/mL (primary endpoint) and <400 copies/mL were achieved by a significantly greater proportion of patients receiving etravirine 200 mg twice daily plus background therapy (BT) than placebo plus BT, according to the planned pooled and individual 24-week analyses of two large, well designed, continuing phase III trials (DUET-1 and DUET-2). In the pooled 24-week analysis, patients receiving etravirine plus BT achieved a significantly greater mean reduction in viral load from baseline and a significantly greater mean increase in CD4+ cell counts from baseline than patients receiving placebo plus BT. The pooled and individual findings of the DUET studies at 48 weeks indicate that the efficacy of etravirine is maintained with regard to these endpoints. In the DUET studies, etravirine was generally well tolerated in treatment-experienced patients infected with HIV-1, with a tolerability profile generally similar to that of placebo. Adverse events were mostly of mild or moderate severity.

Antiretroviral combinations implicated in emergence of the L74I and L74V resistance mutations in HIV-1-infected patients

BACKGROUND

Very little is known about the alternative L74I mutation. This lack of knowledge has led to contradictory and confusing attitudes to L74I; although this mutation is not listed by the International AIDS Society - USA, it is increasingly included in several resistance algorithms.

OBJECTIVE

To compare and clarify the role of each antiretroviral compound and the resistance background in the emergence of the L74I and L74V mutations.

METHODS

We focused on the treatment used at the exact time of any L74V or L74I emergences in 74 patients, and we compared the use of each nucleoside reverse transcriptase inhibitor (NRTI) separately and in combination between the 74I and the 74V groups. The distribution of other NRTI and non-NRTI mutations between the two groups was also analysed.

RESULTS

A majority of L74I mutations is selected under the zidovudine plus abacavir combination or under tenofovir with thymidine analogue mutations in the resistance background. The K103N substitution also plays an important role in the L74I emergence when not associated with the other non-NRTI mutations seen in this study: L100I, G190A and Y181C. Didanosine plays the principal role in the L74V emergence.

CONCLUSIONS

This study shows that the L74I and the L74V correspond to two different mutation pathways, conferring probably different resistance and replication advantages on HIV depending on the context. Taking into account more systematically the L74I mutation, whose impact is certainly currently underestimated, would increase our understanding of this substitution and its effects on the drug activity in vivo.

Simplification Strategies to Reduce Antiretroviral drug Exposure: Progress and Prospects

Current US guidelines for initial therapy of HIV type-1 (HIV-1) infection recommend daily, lifelong treatment with a combination of three antiretroviral drugs consisting of two nucleoside analogue reverse transcriptase inhibitors and a non-nucleoside reverse transcriptase inhibitor or a protease inhibitor. Although this approach has been successful in reducing morbidity and mortality from HIV-1 infection, concerns remain about adverse events from chronic drug exposure, the requirement for daily medication adherence, the risk of HIV-1 drug resistance and high treatment costs. The availability of antiretrovirals that are coformulated and dosed once daily have reduced pill burden and have simplified dosing schedules, but have not lowered drug exposure or cost. These limitations have stimulated research into drug-sparing strategies including intermittent therapy and simplified maintenance regimens. Randomized clinical trials have shown greater mortality with intermittent therapy compared with continuous therapy leading to rejection of this strategy. Pilot studies of simplified maintenance therapy with a ritonavir-boosted protease inhibitor alone have shown more promise, although concerns remain. This article reviews progress in the simplification of antiretroviral therapy, recent clinical trial results and prospects for the future.

Novel tight binding PETT, HEPT and DABO-based non-nucleoside inhibitors of HIV-1 reverse transcriptase

Non-nucleoside reverse transcriptase (RT) inhibitors (NNRTIs) are a key component of effective combination antiretroviral therapies for HIV/AIDS. NNRTIs despite their chemical diversity, bind to a common allosteric site of HIV-1 RT, the primary target for anti-AIDS chemotherapy, and noncompetitively inhibit DNA polymerization. NNRTIs currently in clinical use have a low genetic barrier to resistance and therefore, the need for novel NNRTIs active against drug-resistant mutants selected by current therapies is of paramount importance. We describe the chemistry and biological evaluation of highly potent novel phenethylthiazolylthiourea (PETT), 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT) and dihydroalkoxybenzyloxopyrimidine (DABO) derivatives targeting the hydrophobic binding pocket of HIV-1 RT. These NNRTIs were rationally designed by molecular modeling and docking studies using a novel composite binding pocket that predicted how drug-resistant mutations would change the RT binding pocket shape, volume, and chemical make-up and how these changes could affect NNRTI binding. Several ligand derivatization sites were identified for docked NNRTIs that fit the composite binding pocket. The best fit was determined by calculating an inhibition constant (Ludi Ki) of the docked compound for the composite binding pocket. Compounds with a Ludi Ki of <1 microM were identified as the most promising tight binding NNRTIs. These NNRTIs displayed high selective indices with robust anti-HIV-1 activity against the wild-type and drug-resistant isolates carrying multiple RT gene mutations. The high rate of treatment failure due to the emergence of drug resistance mutations makes the discovery of broad-spectrum PETT, HEPT and DABO-based NNRTIs useful as a component of effective combination regimens.

Comparison of genotypic resistance profiles and virological response between patients starting nevirapine and efavirenz in EuroSIDA

OBJECTIVE

To compare virological outcome and genotypic resistance profiles in HIV-1-infected patients starting non-nucleoside reverse transcriptase inhibitor (NNRTI)-containing regimens.

METHODS

NNRTI-naive patients were included who started treatment with nevirapine (NVP) or efavirenz (EFV) with genotypic resistance test results available at time of initiation (baseline). Virological failure was defined as two consecutive values > 500 copies/ml after starting the regimen. Cox models were used to investigate time to virological failure (the first of two values).

RESULTS

A total of 759 patients were included (13% antiretroviral-naive): 389 initiated NVP and 370 initiated EFV. Baseline IAS-USA NNRTI resistance mutations were detected in 3%. Using the Rega algorithm (version 7.1) to interpret resistance, 460 (64%) patients had resistance (full or intermediate) to at least one drug they were starting (69% NVP, 60% EFV, P = 0.011); 287 (74%) NVP and 168 (45%) EFV patients experienced virological failure after treatment initiation, P < 0.001. After adjustment for previous antiretroviral use, previous AIDS, year started NNRTI, CD4 cell count (baseline, nadir), viral load (baseline, maximum), and baseline drug resistance (measured by Rega), the relative hazards (EFV versus NVP) of virological failure was 0.50, 95% confidence interval: 0.39-0.65, P < 0.001. At time of virological failure, comparable levels of NNRTI resistance were detected. The K103N mutation emerged more in patients failing EFV and Y181C in patients failing NVP.

CONCLUSIONS

NVP may be associated with an inferior virological outcome compared to EFV in NNRTI-naive patients with extensive resistance to other drug classes. The profile of NNRTI resistance mutations when virologically failing an NNRTI-containing regimen appears to depend on the NNRTI the patients fail.

HIV drug resistance after the use of generic fixed-dose combination stavudine/lamivudine/nevirapine as standard first-line regimen

Early failures to stavudine/lamivudine/nevirapine used as a generic fixed-dose combination in Mali showed resistance mutations in 50% of cases (mostly M184V and Y181C). No thymidine analogue mutations were seen, suggesting that most nucleoside reverse transcriptase inhibitors could be used in a second-line regimen. This highlights the importance of the accessibility of HIV-RNA assays for monitoring treated patients in resource-poor countries to detect early virological failure in order to preserve future therapeutic options.

Darunavir (TMC114): a new HIV-1 protease inhibitor

Effective combination therapy for HIV/AIDS is now available and has made a major impact on HIV-related mortality and morbidity. The effects of even the most active of antiretroviral drugs are hampered by drug resistance and tolerability issues. Darunavir (TMC114), coadministered with low-dose ritonavir (darunavir/r), is a new HIV-1 protease inhibitor that has been designed to be active against both wild-type and multi-resistant virus. Darunavir/r 600/100 mg b.i.d. in a combination antiretroviral regimen in the POWER trials has provided treatment-experienced patients with substantially greater virological and immunological benefits compared with standard of care. This article reviews the presently available data on darunavir, its pharmacology, pharmacokinetics, drug-drug interactions and clinical trial results, as well as examining darunavir from a health economic perspective.

Reverse transcription of the HIV-1 pandemic

The HIV/AIDS pandemic has existed for >25 years. Extensive work globally has provided avenues to combat viral infection, but the disease continues to rage on in the human population and infected approximately 4 million people in 2006 alone. In this review, we provide a brief history of HIV/AIDS, followed by analysis of one therapeutic target of HIV-1: its reverse transcriptase (RT). We discuss the biochemical characterization of RT in order to place emphasis on possible avenues of inhibition, which now includes both nucleoside and non-nucleoside modalities. Therapies against RT remain a cornerstone of anti-HIV treatment, but the virus eventually resists inhibition through the selection of drug-resistant RT mutations. Current inhibitors and associated resistance are discussed, with the hopes that new therapeutics can be developed against RT.

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

BACKGROUND

Antiretroviral agents active against drug-resistant HIV-1 are needed for treatment-experienced patients. The aim of this trial was to assess the efficacy, safety, and tolerability of TMC125 (etravirine), a non-nucleoside reverse transcriptase inhibitor (NNRTI).

METHODS

DUET-1 is a continuing, multinational randomised, double-blind, placebo-controlled, phase III trial. Treatment-experienced adult patients with virological failure on stable antiretroviral therapy, documented genotypic evidence of NNRTI resistance, viral load over 5000 copies per mL, and three or more primary protease inhibitor mutations were randomly assigned to receive 200 mg TMC125 or placebo twice daily. All patients also received darunavir with low-dose ritonavir and investigator-selected nucleoside reverse transcriptase inhibitors. Enfuvirtide use was optional. The primary endpoint was a confirmed viral load below 50 copies per mL at week 24 (FDA time-to-loss of virological response algorithm). Analyses were done by intention to treat. This trial is registered with ClinicalTrials.gov, with the number NCT00254046.

FINDINGS

612 patients were randomised and treated (304 in the TMC125 group, 308 in the placebo group). By week 24, 42 (14%) patients in the TMC125 group and 56 (18%) in the placebo group had discontinued, mainly due to virological failure. At week 24, 170 (56%) patients in the TMC125 group and 119 (39%) patients in the placebo group achieved a confirmed viral load of less than 50 copies per mL (difference in response rates 17%; 95% CI 9-25; p=0.005). Most adverse events were mild or moderate in severity. The type and incidence of adverse events, including neuropsychiatric events, seen with TMC125 were generally comparable with placebo, with the exception of rash (61 [20%] patients on TMC125 vs 30 [10%] on placebo) and diarrhoea (36 [12%] patients on TMC125 vs 63 [20%] on placebo).

INTERPRETATION

In treatment-experienced patients with NNRTI resistance, treatment with TMC125 achieved better virological suppression at week 24 than did placebo. The safety and tolerability profile of TMC125 was generally comparable with placebo.

Efficacy and safety of TMC125 (etravirine) in treatment-experienced HIV-1-infected patients in DUET-2: 24-week results from a randomised, double-blind, placebo-controlled trial

BACKGROUND

TMC125 (etravirine) is a non-nucleoside reverse-transcriptase inhibitor (NNRTI) with activity against NNRTI-resistant HIV-1 in phase IIb trials. The aim of DUET-2 is to examine the efficacy, tolerability, and safety of TMC125 in treatment-experienced patients.

METHODS

In this continuing randomised, double-blind, placebo-controlled, phase III trial, HIV-1-infected patients on failing antiretroviral therapy with evidence of resistance to currently available NNRTIs and at least three primary protease inhibitor mutations were eligible for enrolment if on stable (8 weeks unchanged) antiretroviral therapy with plasma HIV-1 RNA greater than 5000 copies per mL. Patients were randomly assigned to receive either TMC125 (200 mg) or placebo, each given twice daily with darunavir-ritonavir, investigator-selected nucleoside/nucleotide reverse transcriptase inhibitors, and optional enfuvirtide. The primary endpoint was the proportion of patients with confirmed viral load below 50 copies per mL at week 24 (FDA time-to-loss of virological response algorithm). Analyses were by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00255099.

FINDINGS

591 patients were randomised and treated (295 patients in the TMC125 group and 296 in the placebo group). By week 24, 51 (17%) patients in the TMC125 group and 73 (25%) in the placebo group had discontinued, mainly because of virological failure. 183 (62%) patients in the TMC125 group and 129 (44%) in the placebo group achieved confirmed viral load below 50 copies per mL at week 24 (difference 18%, 95% CI 11-26; p=0.0003). The type and frequency of adverse events were much the same in the two groups.

INTERPRETATION

In treatment-experienced patients, treatment with TMC125 led to better virological suppression at week 24 than did placebo. The safety and tolerability profile of TMC125 was generally comparable with placebo.

Transmitted Resistance: An Overview and Its Potential Relevance to the Management of HIV-Infected Persons in Resource-Limited Settings

Transmitted resistance has become an important clinical problem in developed countries with long histories of antiretroviral use. In resource-limited settings, it is a foreseeable, if not insidiously emerging, issue. Any transmission route or currently approved antiretroviral drug may be involved. The clinical relevance of polymorphisms that commonly occur at sites known to be associated with resistance, and peculiarities of the non-B subtypes, are incompletely understood. Adverse clinical consequences that have been demonstrated with transmitted resistance include an increased risk of failing initial therapy and further development of resistance. Although treatment outcomes can be optimized by baseline resistance testing and virologic monitoring, these are impractical in most resource-limited settings at this time. The scale and impact of transmitted resistance can probably be reduced by comprehensive prevention and management strategies. Equally germane are epidemiological and clinical studies to extend understanding of the dynamics, clinical implications, and management of transmitted resistance.

The pharmacology of HIV drug resistance

Drug resistance to human immunodeficiency virus (HIV) is a major factor in the failure of antiretroviral therapy.1 In order for practitioners to provide effective pharmaceutical care to their HIV patients, it is essential that they understand the mechanisms of HIV drug resistance as well as the various factors that can contribute to its emergence. This article is based on didactic content from the infectious disease section of the Integrated Sequence II Course in the PharmD program at South University. In the course, students are first given an overview that includes key structural components of HIV and a discussion of the HIV life cycle. A detailed presentation on the pharmacology of the various classes of antiretroviral agents follows. The clinical impact and prevalence of HIV drug resistance is then discussed along with factors that might contribute to it. Mechanisms of drug resistance for each class of antiretroviral agents are presented in detail followed by a discussion of the basis and clinical utility of HIV drug resistance testing. Finally, new targets for HIV pharmacotherapy are presented along with an overview of new antiretroviral agents that are being developed. Content taught in lecture is reinforced by relevant case studies that students work on in small groups during the recitation period.

Modulation of human immunodeficiency virus type 1 synergistic inhibition by reverse transcriptase mutations

Synergy between the anti-human immunodeficiency virus type 1 (HIV) nucleoside reverse transcriptase (RT) inhibitors (NRTIs) and nonnucleoside RT inhibitors (NNRTIs) results from a general mechanism in which NNRTIs inhibit ATP-mediated removal of NRTIs from chain-terminated primers by decreasing the maximum rate of removal, thus sustaining NRTI chain termination. With this molecular mechanism of synergy, beta-D-(+)-3'-azido-3'-deoxythymidine monophosphate (AZTMP) removal was examined in the context of clinically relevant RT mutants. The IC50 value for inhibition by nevirapine against wild-type (WT) RT in our removal assay was 3 microM, but this concentration had no effect on removal by the nevirapine-resistant Y181C mutant. Rather, a approximately 83-fold increase in nevirapine was required to decrease the rate of removal by 50% for this mutant. Efavirenz displayed a 100 nM IC50 value against WT and the efavirenz-sensitive Y181C mutant, but the efavirenz-resistant mutants K103N and K103N/Y181C required a 6-fold increase in efavirenz concentration to achieve the same effect. A newer generation NNRTI, TMC125, showed potency (55 nM) against WT and all mutants, paralleling the activity of this inhibitor relative to nevirapine and efavirenz in cell culture. When tested against the AZT-resistant mutant, all NNRTIs inhibited removal by greater than 50%, showing that this mutant is hypersensitive to NNRTIs. Altogether these results illustrate that both the NNRTI and NRTI mutations can modulate chain termination. This demonstrates that sustaining synergistic HIV inhibition in combination NRTI/NNRTI therapy requires NNRTIs that are potent against WT virus and possess favorable activity profiles against clinically relevant mutations.

Impact of HIV-1 Reverse Transcriptase Polymorphism at Codons 211 and 228 on Virological Response to Didanosine

Objective

To determine the potential impact of reverse transcriptase (RT) mutations, other than those currently known to confer nucleoside reverse transcriptase inhibitors (NRTIs) resistance, on the virological response to didanosine (ddI).

Design and patients

In the placebo-controlled Jaguar trial, 168 patients were randomly assigned to receive ddI ( n=111) or placebo ( n=57) in addition to their currently failing regimen for 4 weeks.

Methods

The virological response was a reduction of HIV-1 RNA from baseline to week 4. In an univariate analysis, we investigated the impact on the virological response to ddI of all the mutations in the RT gene (codons 21–236), except those known to confer NRTI resistance. Using the removing procedure, with a test for trend (Jonckheere's test), a new potential score was calculated incorporating all potential mutations associated to the week 4 virological response.

Results

Two RT polymorphisms were associated with a reduced virological response to ddI, R211A/D/G/K/S and L228H/M/R, and one with a better virological response: F214L. A mutation score (M41L+D67N+T69D-K70R +L74V-M184V/I+T215Y/F+K219Q/E+R211A/D/G/K/S+ L228H/M/R), including two RT polymorphisms not previously described to be associated with ddI resistance (211 and 228) and RT mutations previously described, was associated with a continuum of virological response and increased the predictability of virological response to ddI.

Conclusion

RT polymorphisms should be taken into account to define algorithms able to correctly define resistance to NRTIs and more specifically ddI.

TMC125 displays a high genetic barrier to the development of resistance: evidence from in vitro selection experiments

TMC125 is a potent new investigational nonnucleoside reverse transcriptase inhibitor (NNRTI) that is active against human immunodeficiency virus type 1 (HIV-1) with resistance to currently licensed NNRTIs. Sequential passage experiments with both wild-type virus and NNRTI-resistant virus were performed to identify mutations selected by TMC125 in vitro. In addition to "classic" selection experiments at a low multiplicity of infection (MOI) with increasing concentrations of inhibitors, experiments at a high MOI with fixed concentrations of inhibitors were performed to ensure a standardized comparison between TMC125 and current NNRTIs. Both low- and high-MOI experiments demonstrated that the development of resistance to TMC125 required multiple mutations which frequently conferred cross-resistance to efavirenz and nevirapine. In high-MOI experiments, 1 muM TMC125 completely inhibited the breakthrough of resistant virus from wild-type and NNRTI-resistant HIV-1, in contrast to efavirenz and nevirapine. Furthermore, breakthrough of virus from site-directed mutant (SDM) SDM-K103N/Y181C occurred at the same time or later with TMC125 as breakthrough from wild-type HIV-1 with efavirenz or nevirapine. The selection experiments identified mutations selected by TMC125 that included known NNRTI-associated mutations L100I, Y181C, G190E, M230L, and Y318F and the novel mutations V179I and V179F. Testing the antiviral activity of TMC125 against a panel of SDMs indicated that the impact of these individual mutations on resistance was highly dependent upon the presence and identity of coexisting mutations. These results demonstrate that TMC125 has a unique profile of activity against NNRTI-resistant virus and possesses a high genetic barrier to the development of resistance in vitro.

Beyond efficacy: the impact of combination antiretroviral therapy on quality of life

Combination antiretroviral therapy (ART) with two nucleoside reverse transcriptase inhibitors (NRTIs) plus a protease inhibitor (PI) significantly improved the prognosis of patients with HIV. Nevertheless, the usefulness of the first PIs was sometimes compromised by poor tolerability, high pill burden, frequent dosing, and food and fluid restrictions. Consequently, initial ART choices evolved toward simpler PI-sparing regimens incorporating non-nucleoside reverse transcriptase inhibitors or triple NRTIs. Because these PI-sparing alternatives also are imperfect, interest in PI-based approaches to initial therapy remains, especially in light of newer PIs that have a more favorable tolerability profile. The better safety and tolerability attributes of the newer PIs suggest that highly effective therapy can be administered while preserving patients' health-related quality of life. As long as the virologic activity of these newer PIs is comparable to that of existing options, differentiating features beyond efficacy are important in the choice of an appropriate treatment regimen for patients with HIV.

Genetic barriers to resistance and impact on clinical response

The development of drug resistance and cross-resistance continues to pose a challenge to successful long-term antiretroviral therapy despite the availability of new antiretroviral agents. The genetic barrier to resistance of a regimen does not directly correlate with its effectiveness. For some regimens with a low genetic barrier to resistance, however, the emergence of only 1 or 2 key resistance mutations may confer drug resistance not only to that regimen but also to other agents, thereby limiting subsequent treatment options. In addition to the genetic barrier to resistance, factors such as efficacy, safety, tolerability, convenience, and adherence must be considered when choosing a regimen.

HIV-1 intermittent viraemia in patients treated by non-nucleoside reverse transcriptase inhibitor-based regimen

BACKGROUND

It has been demonstrated that, in patients treated by protease-inhibitor-based regimen, intermittent viraemia occurred frequently and was associated with higher concentrations of residual replication but not with virological failure. Risk factors associated with intermittent viraemia and its impact in patients treated by non-nucleoside-reverse-transcriptase-inhibitor-based (NNRTI) regimen need to be evaluated.

METHODS

We analyzed the occurrence of blips (one HIV-1 RNA > 50 copies/ml with a subsequent value < 50 copies/ml), the level of these blips (between 3 and 50 copies/ml) and their effect on CD4 cell count and the occurrence of virological failure in 43 patients with stable suppression of HIV-1 plasma viraemia (< 50 copies/ml) under NNRTI-based therapy.

RESULTS

Eight out of 43 patients had one episode of blips during the follow-up (median = 350 copies/ml). Comparing patients with and without blips, the median level of HIV-1 RNA at baseline was 7.5 versus 3 copies/ml (P = 0.008), respectively. Patients with blips had a significantly lower CD4 cell count after 12 and 18 months than the others. Plasma concentrations of NNRTI before, during, and after the blips were adequate. In addition, the occurrence of blips was not associated with virological failure.

CONCLUSION

These results suggest that blips may reflect ongoing viraemia of below 50 copies/ml and can impair the CD4 cell count recovery under an NNRTI regimen. The impairment of CD4 cell count recovery seems to be affected more by the occurrence of blips than by the level of viraemia (< 50 copies/ml) itself. Nevertheless, despite a tight genetic barrier for resistance with NNRTI drugs, no virologic failure occurred during the follow-up.

Confronting the emergence of drug-resistant HIV type 1: impact of antiretroviral therapy on individual and population resistance

Resistance to antiretroviral agents, and in particular the increasing levels of transmitted resistant virus could offset the substantial gains won with potent antiretroviral therapy. Primary and acquired antiretroviral resistance rates reflect the relative usage of different antiretroviral drugs in the population, as well as the inherent genetic barrier to the development of resistance associated with individual drugs. Data on antiretroviral resistance rates, gleaned from the growing HIV-1-infected population treated with a continuously increasing number of antiretroviral drugs and drug combinations, provide insights into patient management approaches for delaying the emergence of resistance and minimizing the degree of resistance. Evolving data suggest that the relative ease by which HIV-1 escapes the selective pressure of chronic drug exposure varies for the different antiretroviral drug classes and individual antiretroviral drugs. The development of resistance in vivo can be anticipated based on these data, in conjunction with the individuals treatment history and resistance testing results. These in turn can guide the judicious use of antiretroviral drugs to attain optimal treatment responses and to preserve therapeutic options for the time when antiretroviral-resistant strains emerge. The recent developments of new antiretroviral drugs, including the use of boosted protease inhibitors, suggest that treatment strategies can limit the development of resistance.

Novel [2‘,5‘-Bis-O-(tert-butyldimethylsilyl)-β-d-ribofuranosyl]- 3‘-spiro-5‘ ‘-(4‘ ‘-amino-1‘ ‘,2‘ ‘-oxathiole-2‘ ‘,2‘ ‘-dioxide) Derivatives with Anti-HIV-1 and Anti-Human-Cytomegalovirus Activity

New [2',5'-bis-O-(tert-butyldimethylsilyl)-beta-d-ribofuranosyl]-3'-spiro-5' '-(4''-amino-1'',2''-oxathiole-2'',2''-dioxide) (TSAO) derivatives substituted at the 4' '-amino group of the spiro moiety with different carbonyl functionalities have been designed and synthesized. Various synthetic procedures, on the scarcely studied reactivity of the 3'-spiroaminooxathioledioxide moiety, have been explored. The compounds were evaluated for their inhibitory effect on both wild-type and TSAO-resistant HIV-1 strains, in cell culture. The presence of a methyl ester (10) or amide groups (12) at the 4''-position conferred the highest anti-HIV-1 activity, while the free oxalyl acid derivative (11) was 10- to 20-fold less active against the virus. In contrast, the presence at this position of (un)substituted ureido or acyl groups markedly diminished or annihilated the anti-HIV-1 activity. Surprisingly, some of the target compounds also showed inhibition of human cytomegalovirus (HCMV) replication at subtoxic concentrations. This has never been observed previously for TSAO derivatives. In particular, compound 26 represents the first TSAO derivative with dual anti-HIV-1 and -HCMV activity.

TMC125, a novel next-generation nonnucleoside reverse transcriptase inhibitor active against nonnucleoside reverse transcriptase inhibitor-resistant human immunodeficiency virus type 1

Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are potent inhibitors of human immunodeficiency virus type 1 (HIV-1); however, currently marketed NNRTIs rapidly select resistant virus, and cross-resistance within the class is extensive. A parallel screening strategy was applied to test candidates from a series of diarylpyrimidines against wild-type and resistant HIV strains carrying clinically relevant mutations. Serum protein binding and metabolic stability were addressed early in the selection process. The emerging clinical candidate, TMC125, was highly active against wild-type HIV-1 (50% effective concentration [EC50] = 1.4 to 4.8 nM) and showed some activity against HIV-2 (EC50 = 3.5 microM). TMC125 also inhibited a series of HIV-1 group M subtypes and circulating recombinant forms and a group O virus. Incubation of TMC125 with human liver microsomal fractions suggested good metabolic stability (15% decrease in drug concentration and 7% decrease in antiviral activity after 120 min). Although TMC125 is highly protein bound, its antiviral effect was not reduced by the presence of 45 mg of human serum albumin/ml, 1 mg of alpha1-acid glycoprotein/ml, or 50% human serum. In an initial screen for activity against a panel of 25 viruses carrying single and double reverse transcriptase amino acid substitutions associated with NNRTI resistance, the EC50 of TMC125 was <5 nM for 19 viruses, including the double mutants K101E+K103N and K103N+Y181C. TMC125 also retained activity (EC50 < 100 nM) against 97% of 1,081 recent clinically derived recombinant viruses resistant to at least one of the currently marketed NNRTIs. TMC125 is a potent next generation NNRTI, with the potential for use in individuals infected with NNRTI-resistant virus.

PHI-443: A Novel Noncontraceptive Broad-Spectrum Anti-Human Immunodeficiency Virus Microbicide1

PHI-443 (N'-[2-(2-thiophene)ethyl]-N'-[2-(5-bromopyridyl)] thiourea) is a rationally designed novel thiophene thiourea nonnucleoside reverse transcriptase inhibitor (NNRTI) with potent anti-HIV activity against the wild-type and drug-resistant primary clinical human immunodeficiency virus (HIV-1) isolates. This study examined the potential utility of PHI-443 as a nonspermicidal microbicide for prevention of sexual transmission of HIV. Our goal in this study was to test the effects of PHI-443 on in vivo sperm functions under conditions shown to inactivate viruses in human cells. PHI-443 completely prevented the vaginal transmission of a genotypically and phenotypically drug-resistant HIV-1 isolate in the humanized severe combined immunodeficient (Hu-SCID) mouse model of sexually transmitted AIDS. Exposure of human sperm to PHI-443 at doses 30 000 times higher than those that yield effective concentrations against the AIDS virus had no adverse effect on sperm motility, kinematics, cervical mucus penetrability, or the viability of vaginal and cervical epithelial cells. Exposure of rabbit semen to PHI-443 either ex vivo or in vivo had no adverse impact on in vivo fertilizing ability in the rabbit model. Reproductive indices (i.e., pregnancy rate, embryo implantation, and preimplantation losses) were not affected by pretreatment of rabbit semen with PHI-443. Likewise, intravaginal application of 2% PHI-443 via a self-emulsifying gel at the time of artificial insemination resulted in healthy offspring with no apparent peri- or postnatal repercussions. Repeated intravaginal administration of 0.5%- 2% PHI-443 gel was found to be safe in rabbits and lacked systemic absorption. PHI-443 has clinical potential as a prophylactic broad-spectrum anti-HIV microbicide without contraceptive activity.

The impact of initial highly active antiretroviral therapy on future treatment sequences in HIV infection

OBJECTIVES

To determine whether the initial use of non-nucleoside reverse transcriptase inhibitors (NNRTI) or protease inhibitors (PI) differentially influences subsequent HIV therapy.

DESIGN

A cohort study using a prospective clinical database in a university-based HIV clinic.

SUBJECTS

A total of 440 HIV-seropositive patients, naive or nucleoside experienced, initiating therapy with either an NNRTI or PI between January 1998 and July 2003 and followed to December 2003.

MAIN OUTCOME MEASURES

Time until stopping the first regimen and until exposure to all antiretroviral classes (excluding tenofovir and enfuvirtide) according to the type of initial regimen.

RESULTS

A total of 291 subjects initiated HAART with PI and 149 with NNRTI; median follow-up 3.1 and 2.3 years, respectively. Subjects starting NNRTI remained on their initial regimens longer (median time to change 2.1 versus 1.6 years; log rank P = 0.03). Overall, subjects initiating NNRTI-based regimens were less likely to alter their therapy. Previous nucleoside exposure was an important predictor of treatment modification. Subjects initiating NNRTI-based HAART were also less likely to experience virological failure than those initiating PI-based HAART. Individuals starting with NNRTI were exposed to fewer regimens (15 versus 25% received three or fewer regimens), and showed a trend towards lower rates of three-class exposure (7 versus 12%).

CONCLUSION

There is a high rate of treatment modification among patients initiating HAART. The initial use of NNRTI-based HAART was associated with more durable treatment and lower rates of virological failure, which may translate into a reduced need for multiple salvage therapies.

Evolution of human immunodeficiency virus type 1 (HIV-1) resistance mutations in nonnucleoside reverse transcriptase inhibitors (NNRTIs) in HIV-1-infected patients switched to antiretroviral therapy without NNRTIs

We studied the evolution of nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance mutations among 29 human immunodeficiency virus type 1 (HIV-1)-infected patients who experienced virologic failure when receiving an NNRTI-containing regimen (nevirapine, delavirdine, or efavirenz) and subsequently switched to antiretroviral therapy without NNRTIs. Genotypic resistance was determined from plasma samples collected at the time of NNRTI withdrawal (baseline) and during follow-up. At baseline, 83% of patients had more than two thymidine analog resistance mutations (TAMs), and all had NNRTI resistance mutations. Mutations at codons 103, 181, and 190 were found in 62, 62, and 34% of the patients, respectively. Follow-up samples were available after a median time of 6 months in all patients and at 12 months in 22 patients. The mean number of resistance mutations to NNRTIs was significantly lower at months 6 (1.34 +/- 1.04) and 12 (1.18 +/- 1.05) than at month 0 (2.03 +/- 1.02) (P < 0.009). The percentages of patients with at least one NNRTI resistance mutation were 100, 76, and 73% at baseline, month 6, and month 12, respectively (P < 0.0044). Overall, 70% of the patients had a mutation at codon 103 or 181 at month 12. The mean number of TAMs did not vary significantly during follow-up. Our data show that, in the context of maintained antiretroviral therapy, NNRTI resistance mutations persist in two-thirds of the patients in spite of NNRTI withdrawal. These results argue for the low impact of NNRTI resistance mutations on viral fitness and suggest that resistance mutations to different classes of drugs are associated on the same genome, at least in some of the resistant strains.

Modeling the time course of CD4 T-lymphocyte counts according to the level of virologic rebound in HIV-1-infected patients on highly active antiretroviral therapy

OBJECTIVE

To study the influence of the level of virologic rebound during combination antiretroviral therapy on the time course of the CD4 count.

METHODS

Between January 1997 and December 1999, we enrolled 3736 patients from the French Hospital HIV Database who had an undetectable viral load on a first course of highly active antiretroviral therapy (HAART). Four levels of virologic rebound were defined on the basis of viral load values during the year following initial undetectability on HAART: group 1, all viral loads <500 copies/mL; group 2, all viral loads <5000 copies/mL; group 3, all viral loads <10,000 copies/mL; and group 4, at least 1 viral load >10,000 copies/mL. We developed a continuous time-homogeneous Markov process with 5 reversible stages defined by CD4 count intervals.

RESULTS

CD4 counts increased continuously over time in each group. The smaller the virologic rebound, the stronger was the increase in the CD4 count (P < 0.0001). The mean CD4 cell count increments between months 2 and 6 were 26, 20, 11, and 2 cells/mm3 in groups 1, 2, 3, and 4, respectively. The rate of gain fell after month 6 and was almost nil in group 4.

CONCLUSION

After achieving an undetectable viral load on HAART, immunologic reconstitution is possible whatever the subsequent level of viral replication, except among patients with high-level rebound, meaning that in patients with a long history of antiretroviral therapy and a reduced choice of antiretroviral drugs due to acquisition of resistances, delay in antiretroviral therapy switch can be possible in patients with low or intermediate rebound.

Antiretroviral drug resistance testing in adults infected with human immunodeficiency virus type 1: 2003 recommendations of an International AIDS Society-USA Panel

New information about the benefits and limitations of testing for resistance to human immunodeficiency virus (HIV) type 1 (HIV-1) drugs has emerged. The International AIDS Society-USA convened a panel of physicians and scientists with expertise in antiretroviral drug management, HIV-1 drug resistance, and patient care to provide updated recommendations for HIV-1 resistance testing. Published data and presentations at scientific conferences, as well as strength of the evidence, were considered. Properly used resistance testing can improve virological outcome among HIV-infected individuals. Resistance testing is recommended in cases of acute or recent HIV infection, for certain patients who have been infected as long as 2 years or more prior to initiating therapy, in cases of antiretroviral failure, and during pregnancy. Limitations of resistance testing remain, and more study is needed to refine optimal use and interpretation.

Interruption of nonnucleoside reverse transcriptase inhibitor (NNRTI) therapy for 2 months has no effect on levels of human immunodeficiency virus type 1 in plasma of patients harboring viruses with mutations associated with resistance to NNRTIs

A 2-month interruption of only nonnucleoside reverse transcriptase inhibitors (NNRTIs) for patients carrying mutations associated with resistance to NNRTIs was followed by no change in either viral load or CD4 cell counts. These data suggest that these compounds have lost all of their in vivo antiviral activity in such cases.

HIV-1 Reverse Transcriptase and Protease Resistance Mutations Selected during 16–72 Weeks of Therapy in Isolates from Antiretroviral Therapy-Experienced Patients Receiving Abacavir/Efavirenz/Amprenavir in the CNA2007 Study

Objective

To determine HIV-1 reverse transcriptase (RT) and protease (PRO) mutations selected in isolates from antiretroviral therapy (ART)-experienced patients receiving an efavirenz/abacavir/amprenavir salvage regimen.

Methods

Open-label, single arm of abacavir, 300 mg twice daily, amprenavir, 1200 mg twice daily and efavirenz, 600 mg once daily, in ART-experienced patients of which 42% were non-nucleoside reverse transcriptase inhibitor-naive. The virology population examined consisted of all patients who took at least 16 weeks of study drugs (n=74). Plasma population sequencing was carried out at baseline and last time point at which patients were still taking the three study drugs ± other ART. The median follow-up was 48 weeks (range week 16–72).

Results

Baseline (n=73) and on-therapy (n=49) genotypes were obtained. By 48 weeks, 51% of isolates had ≥3 non-nucleoside reverse transcriptase inhibitor (NNRTI) mutations. NNRTI mutations selected on therapy were K103N (51%), substitutions at position 190 (17/49, 35%): G to A (n=11) / S (n=4) / E (n=1) and T (n=1); L100I (37%) and V108I (20%) mutations. P225H was not observed in this study. L100I and G190A/S/E/T mutations were rarely detected in the same viral population and baseline Y181C favoured the G190 mutations (OR=8.9, P<0.001), rather than the L100I. The NRTI mutations selected were in accordance with abacavir known resistance profile, no new TAMs were observed, new L74V or I mutations developed in 39 and 16% of isolates, respectively, however, new M184V mutations were only detected in isolates from two patients, one of whom had added lamivudine + didanosine. M184V was common at baseline (55%) and maintained in 22/27 (81%) isolates (five of these 22 added lamivudine or didanosine, or both). The PRO mutations selected were in accordance with the distinct resistance profile of amprenavir compared with other protease inhibitors. Mutations D30N, G48V, N88D/S, L90M and I54V were de-selected, and mutations I50V, I or V to 54M/L, I84V, M46I/L, L33F, I47V as well mutations at position 10 were observed in 20/49 (41%) isolates.

Conclusion

Prior NNRTI and NRTI therapy influences the pathway of resistance to efavirenz. In this study, the prevalence of mutations selected by efavirenz were different from those described in less ART-experienced patients. Baseline Y181C was associated with the development of mutations at position 190, but not L100I or K103N. In this patient population, abacavir with efavirenz preferentially selected for L74V but not for thymidine analogue mutations. M184V was rarely selected and was maintained in only 77% of patients who did not add lamivudine or didanosine. Finally, amprenavir-specific mutations were selected in the background of other primary protease inhibitor mutations, confirming the distinct resistance profile of amprenavir.

Comparison of nevirapine- and efavirenz-containing antiretroviral regimens in antiretroviral-naïve patients: a cohort study

OBJECTIVE

Efavirenz (EFV) was superior to nevirapine (NVP) in two recent cohort studies; but data from clinical trials suggest that three studies are needed to validate cohort results. We performed a cohort analysis comparing time to treatment failure and change in plasma HIV-1 RNA from baseline in antiretroviral therapy (ART)-naïve individuals treated with NVP- or EFV-containing regimens.

METHOD

A cohort analysis of three observational databases (N = >10,000 patients) found 1,078 ART-naïve individuals treated with NVP-containing (n = 523) or EFV-containing (n = 555) regimens. Patients were evenly matched and received at least three antiretroviral agents. The primary endpoint was time to treatment failure defined as a rebound in plasma HIV-1 RNA > 400 copies/mL. Other endpoints were change in plasma HIV-1 RNA from baseline and percent with plasma HIV-1 RNA <400 copies/mL over time. Potential confounding variables were analyzed using the Cox proportional hazards model.

RESULTS

Compared to EFV, NVP patients had a shorter time to treatment failure (307 days vs. 589 days; p <.001), less decrease in plasma HIV-1 RNA (-0.51 log vs. -1.32 log; p <.001), and fewer patients with plasma HIV-1 RNA < 400 copies/ mL (45% vs. 51%; p <.001). Significant factors for failure were baseline CD4 count (per 100 cell increase) or viral load (per log increase), treatment center, and year of entry (p <.05 for all comparisons). Race, gender, and background nucleoside use were insignificant factors. Multivariate analysis that included significant factors for failure demonstrated improved relative hazard with EFV compared to NVP (odds ratio = 0.50, p <.001).

CONCLUSION

EFV-containing antiretroviral regimens were associated with superior clinical outcome, as measured by time to treatment failure. Results are commensurate with other large cohort studies comparing EFV and NVP.

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

OBJECTIVE

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

RESULTS

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

CONCLUSIONS

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

Genotypic and Phenotypic Resistance Patterns in Early-Stage HIV-1-Infected Patients Failing Initial Therapy with Stavudine, Didanosine and Nevirapine

The objectives of this study were to determine the genotypic and phenotypic patterns of resistance in a group of early-stage antiretroviral-naive patients failing initial therapy with didanosine, stavudine and nevirapine. These patterns of resistance were determined at baseline and at time of virological failure in 89 antiretroviral-naive patients with CD4 cells >500 cells/ml and viral load >5000 copies/ml who received initial antiretroviral therapy with didanosine plus stavudine and nevirapine as part of the SCAN study, and who failed after having reached undetectable plasma levels (<200 copies/ml). Of the 89 patients recruited in the SCAN study, 14 (16%) developed a virological failure after reaching a viral load below 200 copies/ml after a median of 20 months of follow-up. At baseline, none of these 14 patients had genotypic resistance. At time of failure, six out of 14 (43%) failing patients had wild-type genotype and no phenotypic resistance. Suboptimal compliance could be documented in four of these six patients. Seven patients (50%) had nevirapine resistance mutations (mainly K103N [4/7], Y181C/I [2/7], G190A/S [2/7] and V108I [1/7]) associated with phenotypic high-level resistance to nevirapine, delavirdine and efavirenz (nevirapine >47.4-to 58.1-fold, delavirdine >74.4- to 168.9-fold and efavirenz >56.0- to 347.2-fold). Four of these seven patients also had thymidine analogue-associated mutations (TAM) (T215Y/F [2/4], M41L [1/4], D67N [2/4] and K70R [1/4]). Finally, one patient (7%) had exclusively TAM mutations (M41L). None of the patients developed mutations associated with didanosine resistance or phenotypic resistance to didanosine or stavudine. Suboptimal compliance or selection of nevirapine resistance often with TAM mutations was frequently associated with virological failure in a cohort of early-stage chronic HIV-1-infected patients treated with a protease inhibitor-sparing regimen.