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

Identification of new genotypic cut-off levels to predict the efficacy of lopinavir/ritonavir and darunavir/ritonavir in the TITAN trial

BACKGROUND

Genotypic algorithms used to predict the clinical efficacy of lopinavir/ritonavir (LPV/r) have included a range of mutation lists and efficacy endpoints. Normally, HIV clinical trials are powered to detect a difference between treatment arms of 10-12% for the endpoint of viral load suppression <50 HIV-1 RNA copies/mL. The TITAN trial evaluated LPV/r vs. darunavir/ritonavir (DRV/r) in treatment-experienced patients with viral load >1000 copies/mL. This analysis aimed to re-evaluate resistance algorithms for LPV/r in the TITAN trial.

METHODS

Baseline genotype data were classified using seven genotypic resistance algorithms: International AIDS Society USA (IAS-USA) LPV mutations (current cut-off=6), Abbott 2007 mutation list (cut-off=3), ANRS mutations (cut-off=4), FDA mutations (cut-off=3), Stanford, REGA and IAS-USA major protease inhibitor (PI) mutations. Efficacy in the TITAN trial (HIV-1 RNA <50 copies/mL at week 48) was correlated with the number of mutations from each list, to show the 'efficacy advantage cut-off level': the number of mutations from each list associated with a difference in efficacy between treatment arms of at least 12%.

RESULTS

Multivariate logistic regression analysis identified lower genotypic cut-off levels than previously reported where there was at least 12% lower efficacy for LPV/r vs. DRV/r. These efficacy advantage cut-off levels were: IAS-USA LPV mutations, cut-off=3; Abbott 2007, cut-off=2; ANRS LPV, cut-off=3; FDA LPV mutations, cut-off=2; major IAS-USA PI mutations, cut-off=1; Stanford algorithm, cut-off=low-level LPV resistance; REGA algorithm, cut-off=intermediate-level LPV resistance. There were linear falls in HIV-1 RNA suppression rates with rising mutation counts in the TITAN, French LPV ATU, BMS-045 and RESIST trials.

CONCLUSIONS

The analysis identified more sensitive cut-off levels for LPV genotypic algorithms, below those currently used.

[Interpreting methodological and statistical considerations in studies of rescue therapy]

The methodology used in studies of rescue therapy is sometimes complex. This is because of the heterogeneity of objectives and options. Firstly, the definition of failure has multiple interpretations and subtle distinctions. Secondly, the aim of treatment in these patients has varied according to the available treatment options in each case and at each moment of time. Lastly, the methodology used to develop these studies of rescue therapy has varied over time in line with changes in their aims and options. Currently, a new change can be expected to adjust to the current situation, since the number of therapeutic options for rescue therapy has substantially increased in the last year. The present review discusses changes in the design of these studies, the main methodological issues to be taken into account and the recommendations on this subject.

Newer antiretroviral agents and how to use them

Several relatively new antiretroviral drugs have been approved or are under investigation. These include nucleoside and nonnucleoside reverse transcriptase inhibitors, protease and integrase strand transfer inhibitors, CCR5 antagonists, and an entirely new class of maturation inhibitors. Although most of these drugs were developed for patients with drug-resistant HIV-1, some have demonstrated a potential role for those starting treatment for the first time. This review incorporates data from the most recent treatment guidelines, peer-reviewed publications, and recent presentations at research meetings about some of these relatively new and emerging antiretroviral agents and offers strategies for incorporating them into clinical practice.

The fusion inhibitor enfuvirtide in recent antiretroviral strategies

PURPOSE OF REVIEW

The purpose of this review is to discuss recent pharmacological, virological, and clinical data that concern enfuvirtide usage in different antiretroviral combinations.

RECENT FINDINGS

Randomized, recent trials in multidrug-experienced patients suggest that antiretroviral combinations with enfuvirtide have excellent virological responses with new antiretroviral compounds, including darunavir, etravirine, raltegravir, vicriviroc, and maraviroc. Trials confirm long-term safety, in spite of moderate injection-site reactions or pain, and lack of significant interactions. Preliminary data suggest that switching from enfuvirtide to raltegravir is effective and using enfuvirtide in prophylaxis of mother-to-child transmission is well tolerated. To administer enfuvirtide in an intensification strategy in antiretroviral-naïve or experienced populations may accelerate virological decline.

SUMMARY

Dosage adaptations to renal insufficiency are not necessary with enfuvirtide. Spinal fluid concentrations and ombilic cord passage are negligible. Durability of virological responses with enfuvirtide in combinations has been confirmed, in spite of injection-site reactions and twice daily subcutaneous administration. Enfuvirtide should be used with at least one other fully active drug in optimized background therapy in multidrug-experienced populations, a possible exception being with entry inhibitors, which may further benefit from the addition of a third active drug. Data concerning enfuvirtide in antiretroviral combinations show accelerated viral load decline, and the possibility of switching from enfuvirtide to raltegravir without modification of optimized background therapy.

Efficacy and safety of darunavir and etravirine in an antiretroviral multi-experienced youth with vertically HIV-1 infection

Multiclass-drug resistance, often caused by poor treatment compliance, is a challenging problem in all categories of HIV-infected patients. Selective pressure is higher in youth for both biological and behavioral reasons. We report the case of a 15-year-old Caucasian male, with vertically acquired HIV-1 infection, who failed several lines of antiretroviral therapy and was successfully treated with darunavir/ritonavir and etravirine.

[Darunavir in patients with advanced HIV and multiresistance. The POWER, DUET and BENCHMRK studies]

Darunavir is a new protease inhibitor. This drug is highly active against wild-type and multiresistant HIV strains, binds strongly to the HIV-1 protease, has extremely high affinity for the protease and, when enhanced by subtherapeutic doses of ritonavir, has a favorable resistance profile differing from that of current protease inhibitors (PIs). After determining the optimal dose, phase IIb clinical trials (POWER studies 1 and 2) observed much higher virological and immunological efficacy with darunavir than with the comparator PIs. The results of a phase III clinical trial (POWER 3) provide further support for the safety and efficacy of darunavir, and the three POWER studies demonstrate the high genetic barrier of this drug against mutations conferring resistance to other PIs, although the baseline sensitivity of darunavir and the specific mutations to this PI influence the virological response. Better therapeutic responses have been obtained when there are two or more antiretroviral drugs active against multiresistant HIV strains. The phase III trials (DUET 1 and 2), in which darunavir was administered with the new nonnucleoside reverse transcriptase inhibitor, etravirine, found that if these two drugs were administered in highly treatment-experienced patients, a large percentage showed suppression of plasma viremia and immunological recovery. These data have been supported by the results of the BENCHMARK studies, in which darunavir was included in an optimized regimen in a substantial number of patients. In these trials, when darunavir was administered with the integrase inhibitor, raltegravir, undetectable viral loads both in the raltegravir arm and in the control group were substantially improved with respect to the overall results obtained in the control group.

Resistance profiles after different periods of exposure to a first-line antiretroviral regimen in a Cameroonian cohort of HIV type-1-infected patients

Background

The lack of HIV type-1 (HIV-1) viral load (VL) monitoring in resource-limited settings might favour the accumulation of resistance mutations and thus hamper second-line treatment efficacy. We investigated the factors associated with resistance after the initiation of antiretroviral therapy (ART) in the absence of virological monitoring.

Methods

Cross-sectional VL sampling of HIV-1-infected patients receiving first-line ART (nevirapine or efavirenz plus stavudine or zidovudine plus lamivudine) was carried out; those with a detectable VL were genotyped.

Results

Of the 573 patients undergoing VL sampling, 84 were genotyped. The mean number of nucleoside/nucleotide reverse transcriptase inhibitor (NRTI) mutations increased with the duration of ART exposure ( P=0.02). Multivariable analysis showed that patients with a CD4+ T-cell count ≤50 cells/ mm3 at ART initiation (baseline) had a higher mean number of both NRTI and non-NRTI (NNRTI) mutations than those with a baseline CD4+ T-cell count >50 cells/mm3 (2.10 versus 0.56; P<0.0001; and 1.65 versus 0.76; P=0.005, respectively). A baseline CD4+ T-cell count ≤50 cells/mm3 predicted ≥1 NRTI mutation (adjusted odds ratio [AOR] 7.49, 95% confidence interval [CI] 2.20-32.14), ≥1 NNRTI mutation (AOR 4.25, 95% CI 1.36-15.48), ≥1 thymidine analogue mutation (AOR 8.45, 95% CI 2.16-40.16) and resistance to didanosine (AOR 6.36, 95% CI 1.49-32.29) and etravirine (AOR 4.72, 95% CI 1.53-15.70).

Conclusions

Without VL monitoring, the risk of drug resistance increases with the duration of ART and is associated with lower CD4+ T-cell counts at ART initiation. These data might help define strategies to preserve second-line treatment options in resource-limited settings.

Predictive value of pharmacokinetics-adjusted phenotypic susceptibility on response to ritonavir-enhanced protease inhibitors (PIs) in human immunodeficiency virus-infected subjects failing prior PI therapy

The activities of protease inhibitors in vivo may depend on plasma concentrations and viral susceptibility. This nonrandomized, open-label study evaluated the relationship of the inhibitory quotient (IQ [the ratio of drug exposure to viral phenotypic susceptibility]) to the human immunodeficiency virus type 1 (HIV-1) viral load (VL) change for ritonavir-enhanced protease inhibitors (PIs). Subjects on PI-based regimens replaced their PIs with ritonavir-enhanced indinavir (IDV/r) 800/200 mg, fosamprenavir (FPV/r) 700/100 mg, or lopinavir (LPV/r) 400/200 mg twice daily. Pharmacokinetics were assessed at day 14; follow-up lasted 24 weeks. Associations between IQ and VL changes were examined. Fifty-three subjects enrolled, 12 on IDV/r, 33 on FPV/r, and 8 on LPV/r. Median changes (n-fold) (FC) of 50% inhibitory concentrations (IC(50)s) to the study PI were high. Median 2-week VL changes were -0.7, -0.1, and -1.0 log(10) for IDV/r, FPV/r, and LPV/r. With FPV/r, correlations between the IQ and the 2-week change in VL were significant (Spearman's r range, -0.39 to -0.50; P < or = 0.029). The strongest correlation with response to FPV/r was the IC(50) FC (r = 0.57; P = 0.001), which improved when only adherent subjects were included (r = 0.68; P = 0.001). In multivariable analyses of the FPV/r arm that included FC, one measure of the drug concentration, corresponding IQ, baseline VL, and CD4, the FC to FPV was the only significant predictor of VL decline (P < 0.001). In exploratory analyses of all arms, the area under the concentration-time curve IQ was correlated with the week 2 VL change (r = -0.72; P < 0.001). In conclusion, in PI-experienced subjects with highly resistant HIV-1, short-term VL responses to RTV-enhanced FPV/r correlated best with baseline susceptibility. The IQ improved correlation in analyses of all arms where a greater range of virologic responses was observed.

Effect of steady-state etravirine on the pharmacokinetics and pharmacodynamics of ethinylestradiol and norethindrone

BACKGROUND

Etravirine, a non-nucleoside reverse transcriptase inhibitor (NNRTI) active against NNRTI-resistant HIV, is an inducer of CYP3A4 and an inhibitor of CYP2C9/19.

STUDY DESIGN

The effect of etravirine on the pharmacokinetics and pharmacodynamics of ethinylestradiol and norethindrone was assessed in 30 HIV-negative females. Following a run-in cycle with ethinylestradiol/norethindrone, the pharmacokinetics of ethinylestradiol and norethindrone was assessed on Day 15 of Cycle 2. Etravirine 200 mg bid was coadministered on Day 1 to Day 15 of Cycle 3, with pharmacokinetic assessments of ethinylestradiol, norethindrone and etravirine on Day 15.

RESULTS

When combined with etravirine, the least-squares means (LSM) ratios (90% confidence interval) for ethinylestradiol AUC(24h), C(max) and C(min) were 1.22 (1.13-1.31), 1.33 (1.21-1.46) and 1.09 (1.01-1.18), respectively, compared to administration alone. LSM ratios for norethindrone parameters were 0.95 (0.90-0.99), 1.05 (0.98-1.12) and 0.78 (0.68-0.90), respectively.

CONCLUSION

These changes are not considered clinically relevant. No loss in contraceptive efficacy is expected when coadministered with etravirine.

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.

[Safety and tolerability of darunavir]

Darunavir, previously known as TMC-114, is a new protease inhibitor (PI) with a high affinity for the HIV-1 protease and strong ability to inhibit its action, even in mutated forms. Consequently, this drug is considered to have great intrinsic potency and a high genetic barrier. At the time of writing, data on the tolerability and safety of darunavir come mainly from studies of late rescue therapy (POWER, DUET), which have included more than 1,600 patients. Recent data, relating to shorter time periods, are also available from studies in early treatment-experienced patients (TITAN) and in treatment-naïve patients (ARTEMIS), increasing experience to a further 600 patients. Lastly, more than 4,000 patients who have received darunavir through the Expanded Access Program have allowed the drug's generally good safety and tolerability profile to be defined. In the studies performed to date, darunavir has been well tolerated, with a better profile than that of the PIs used in control groups in terms of adverse effects such as diarrhea, gastrointestinal tolerability and lipid alterations. Moreover, to date, no unexpected severe adverse effects have been reported.

Antiretroviral nephrotoxicities

With the introduction of combination antiretroviral therapy, there have been substantial declines in both morbidity and mortality associated with human immunodeficiency virus (HIV)-1 infection. However, data increasingly indicate that HIV-1-infected individuals are faced with accelerated rates of chronic diseases that afflict the general population such as diabetes mellitus, hypertension, and dyslipidemia, as well as cardiovascular, liver, and kidney diseases. Furthermore, this population is exposed to a variety of adverse effects from long-term use of antiretroviral medications, which may cause clinically important renal toxicities. However, it often is challenging to distinguish antiretroviral-related renal toxicity from either direct effects of HIV-1 on the kidney or from a multitude of non-HIV-related kidney diseases. A timely and coordinated effort by the HIV primary provider and a nephrologist is likely to facilitate the evaluation of HIV-1-infected patients with new kidney problems.

for the Collaborative Group for Clinical Use of HIV Genotype Resistance Test, Zaccarelli M, Lorenzini P, Ceccherini-Silberstein F, Tozzi V, Forbici F, Gori C, Trotta MP, Boumis E, Narciso P, Perno CF, Antinori A. Historical resistance profile helps to predict salvage failure

Background

This study compared the predictive value for treatment failure of extended resistance detected in the current genotype resistance test (GRT) versus those from GRT history in patients with multiple combination anti-retroviral therapy (cART) failures.

Methods

Patients who underwent three GRT between 1999 and 2007 were included. Extended resistance at genotypic sensitivity score (GSS) using the Rega 7.1 interpretation system compared with a non-standard definition (defined as class-wide resistance [CWR] on the basis of International AIDS Society–USA mutations) was assessed both for current and historical GRTs (a combination of mutations was detected in all three tests). The predictive role of extended resistance for treatment failure was evaluated with an adjusted Cox proportional hazard model.

Results

Overall, 177 patients were included. The historical GRT increased the number of patients with extended resistance to all three major drug classes by 25% in comparison with the current GRT. Using the GSS method, the absence of detection of any active drug in any drug class was predictive of failure with both the current and historical GRTs. Similarly, the number of active drugs in the cART regimen after the third resistance test, used as continuous variable, was also predictive of failure. Using both GSS approaches, current genotype had a higher effect than historical genotype on risk of treatment failure. Using the non-standard definition (CWR), historical resistance predicted failure better than current resistance.

Conclusions

Our results provide an epidemiological demonstration that analysis of a combined latest and historical GRT, which also considers archived mutations, might better identify of the more virologically impaired patients in order to assess the best salvage treatment.

Efficacy and safety of etravirine (TMC125) in treatment-experienced HIV-1-infected patients: 48-week results of a phase IIb trial

Forty-eight-week results from a randomized, multicentre, part-blinded, phase IIb clinical trial assessing the efficacy and safety of 400 and 800 mg etravirine twice daily (phase IIb formulation) and optimized background regimen versus standard-of-care regimen are presented. Both etravirine doses demonstrated sustained virological suppression at 48 weeks and a favourable tolerability profile. Etravirine demonstrated higher efficacy than control, irrespective of the number of detectable nonnucleoside reverse transcriptase inhibitor-resistance-associated mutations at baseline or active background antiretrovirals.

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.

HIV/AIDS: the management of treatment-experienced HIV-infected patients: new drugs and drug combinations

The recent availability of new antiretroviral agents for the treatment of human immunodeficiency virus (HIV) infection has increased treatment options and has improved the durability, tolerability, and long-term efficacy of antiretroviral therapy, even among patients with extensive treatment experience and high levels of drug resistance. This expansion of therapeutic options has led to a revision of current treatment guidelines, which now state that the goal of antiretroviral therapy in all patients is suppression of the plasma HIV RNA level to <50 copies/mL. Successful management of infection for treatment-experienced patients with the new agents requires an understanding of their pharmacology and resistance patterns and the appropriate use of laboratory testing to optimize regimen selection. This review discusses the use of recently approved antiretroviral agents in the management of HIV infection in treatment-experienced patients.

Canadian consensus guidelines for the optimal use of etravirine in the treatment of HIV-infected adults

BACKGROUND AND OBJECTIVES

A group of five Canadian physicians with significant experience in HIV management was convened. Their goal was to develop guidance specifically for Canadian HIV-treating physicians on the appropriate use of etravirine (TMC125, Intelence, Tibotec BVBA, Belgium) in adult HIV-infected patients.

METHODS

Evidence from the published literature, conference presentations and expert opinions of the group members were used to develop the recommendations. Feedback on the draft recommendations was obtained from this core group, and from seven other physicians across Canada with clinical HIV treatment expertise and experience in the use of etravirine, as well as two Canadian scientists with HIV expertise. The final recommendations represent the core group's consensus agreement, taking all feedback into consideration.

RESULTS AND CONCLUSIONS

The recommendations were developed to guide physicians in the optimal use of etravirine. The issues considered included HIV disease status, antiretroviral treatment history, drug resistance profiles, predictors of response to etravirine, background antiretroviral regimen and drug-drug interactions.

Efficacy and resistance of recently developed non-nucleoside reverse transcriptase inhibitors for HIV-1

Since the introduction of the HAART, non-nucleoside reverse transcriptase inhibitors (NNRTIs) have played an essential role in treating HIV: their strong antiviral potency, good metabolic profile and low pill burden make them an ideal option in the design of an optimized triple drug regimen. Nonetheless, the currently approved NNRTIs (efavirenz and nevirapine) are weighed by peculiar toxicities, while a low genetic barrier and the development of cross-resistance significantly limits their use in cases of suboptimal adherence. Many drugs are in development and they are all designed with the aim to overcome resistance problems. In this review we present data on virological efficacy and resistance profiles of some of the most promising new molecules: some (such as rilpivirine) are close to being marketed, others are in Phase II trials (IDX899 and RDEA806), others again have just completed preclinical studies and are having their first clinical evaluations (RO-5028, UK-453061 and BILR-355 BS); etravirine is already approved by the US FDA, but it is still not licensed in Europe. Other new molecules (Merck MK-4965, GlaxoSmithKline GW678284 and a pyridazinone derivative by Roche), which are currently in early-development phases, are also briefly described.

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.

Optimal use of raltegravir (Isentress(R)) in the treatment of HIV-infected adults - Canadian consensus guidelines

BACKGROUND AND OBJECTIVES

A meeting of a Canadian group with significant experience and knowledge in HIV management, consisting of five physicians, a pharmacist and an AIDS researcher, was convened. Their goal was to develop guidance for Canadian HIV-treating physicians on the appropriate use of raltegravir (MK-0518, Isentress(R), Merck Frosst Canada Inc) in HIV-infected adults.

METHODS

Evidence from the published literature and conference presentations, as well as expert opinions of the group members, was considered and evaluated to develop the recommendations. Feedback on the draft recommendations was obtained from this core group, as well as from five other physicians and scientists across Canada with expertise in HIV treatment and antiretroviral drug resistance, and experience in the use of raltegravir. The final recommendations represent the core group's consensus agreement once all feedback was considered.

RESULTS/CONCLUSIONS

Recommendations were developed to guide physicians in the optimal use of raltegravir. The issues considered included raltegravir's role in overall treatment strategy, efficacy, durability of effect, rate of viral load reduction, resistance, safety/toxicity, pharmacokinetics and drug interactions.

Anti-HIV drugs: 25 compounds approved within 25 years after the discovery of HIV

In 2008, 25 years after the human immunodeficiency virus (HIV) was discovered as the then tentative aetiological agent of acquired immune deficiency syndrome (AIDS), exactly 25 anti-HIV compounds have been formally approved for clinical use in the treatment of AIDS. These compounds fall into six categories: nucleoside reverse transcriptase inhibitors (NRTIs: zidovudine, didanosine, zalcitabine, stavudine, lamivudine, abacavir and emtricitabine); nucleotide reverse transcriptase inhibitors (NtRTIs: tenofovir); non-nucleoside reverse transcriptase inhibitors (NNRTIs: nevirapine, delavirdine, efavirenz and etravirine); protease inhibitors (PIs: saquinavir, ritonavir, indinavir, nelfinavir, amprenavir, lopinavir, atazanavir, fosamprenavir, tipranavir and darunavir); cell entry inhibitors [fusion inhibitors (FIs: enfuvirtide) and co-receptor inhibitors (CRIs: maraviroc)]; and integrase inhibitors (INIs: raltegravir). These compounds should be used in drug combination regimens to achieve the highest possible benefit, tolerability and compliance and to diminish the risk of resistance development.

Efavirenz--still first-line king?

BACKGROUND

Efavirenz is a potent, safe and tolerable non-nucleoside reverse transcriptase inhibitor (NNRTI) recommended as initial therapy. Recently, several new antiretroviral drugs, including second generation NNRTIs, protease-inhibitors, an integrase-inhibitor and a CCR5 inhibitor, have become or will be shortly available.

OBJECTIVE

This article will review relevant efficacy and safety data of efavirenz compared to these novel agents or certain common alternate drugs currently used as initial therapy in treatment-naive patients.

METHODS

Published articles and conference presentations pertaining to efavirenz and/or the newer antiretroviral agents were evaluated.

RESULTS/CONCLUSIONS

Efavirenz will continue to be preferred initial therapy for now. If longer-term studies of integrase inhibitors and second-generation NNRTIs confirm initial findings, they will eventually supplant efavirenz as preferred first-line agents.

Antiretroviral therapy in HIV-infected patients with multidrug-resistant virus: applying the guidelines to practice

Abstract Current treatment guidelines recommend maintenance of HIV-1 viral load below detectable levels (<50 copies per milliliter), even in extensively treated patients with multidrug-resistant HIV-1. Given recent advances in drug development and the availability of new agents with activity against antiretroviral-resistant HIV-1 viral strains, this goal is increasingly attainable for treatment-experienced patients. A stepwise approach to management of patients harboring antiretroviral-resistant HIV is presented, including assessment of adherence, a description of the use of resistance testing and utilization of new antiretroviral agents.

Inhibition of human immunodeficiency virus type 1 infection by the candidate microbicide dapivirine, a nonnucleoside reverse transcriptase inhibitor

Heterosexual transmission of human immunodeficiency virus (HIV) remains the major route of infection worldwide; thus, there is an urgent need for additional prevention strategies, particularly strategies that could be controlled by women, such as topical microbicides. Potential microbicide candidates must be both safe and effective. Using cellular and tissue explant models, we have evaluated the activity of the nonnucleoside reverse transcriptase inhibitor (NNRTI) dapivirine as a vaginal microbicide. In tissue compatibility studies, dapivirine was well tolerated by epithelial cells, T cells, macrophages, and cervical tissue explants. Dapivirine demonstrated potent dose-dependent inhibitory effects against a broad panel of HIV type 1 isolates from different clades. Furthermore, dapivirine demonstrated potent activity against a wide range of NNRTI-resistant isolates. In human cervical explant cultures, dapivirine was able not only to inhibit direct infection of mucosal tissue but also to prevent the dissemination of the virus by migratory cells. Activity was retained in the presence of semen or a cervical mucus simulant. Furthermore, dapivirine demonstrated prolonged inhibitory effects: it was able to prevent both localized and disseminated infection for as long as 6 days posttreatment. The prolonged protection observed following pretreatment of genital tissue and the lack of observable toxicity suggest that dapivirine has considerable promise as a potential microbicide candidate.

Phenotypic impact of resistance mutations on etravirine susceptibility in HIV patients with prior failure to nonnucleoside analogues

The phenotypic impact on etravirine susceptibility was examined in plasma specimens from 40 nonnucleoside reverse transcriptase inhibitor-experienced HIV patients with distinct nonnucleoside reverse transcriptase inhibitor resistance-associated mutations. Some etravirine resistance-associated mutations produced larger reductions in fold change than others. Y181C in combination with at least one etravirine resistance-associated mutation caused, on average, a 12.6-fold reduced susceptibility to etravirine. Two novel changes, K101H and E399D, significantly diminished etravirine susceptibility. Thus, the original etravirine resistance-associated mutation list should be updated and weighted for a suitable genotypic resistance interpretation.

Pharmacokinetics of Elvitegravir and Etravirine following Coadministration of Ritonavir-Boosted Elvitegravir and Etravirine

Background

This crossover, open-label clinical study evaluated the potential for clinically relevant drug interactions between ritonavir-boosted elvitegravir (elvitegravir/r), an HIV integrase inhibitor, and etravirine, a non-nucleoside reverse transcriptase inhibitor.

Methods

Healthy volunteers were randomized into one of two groups, each with two arms. Group 1 ( n=20) followed a sequence of 10-day dosing of elvitegravir/r (150/100 mg once daily) and elvitegravir/r plus etravirine (200 mg twice daily) or the reverse ( n=10 per sequence). Group 2 ( n=14) followed a sequence of 10-day dosing of etravirine and etravirine plus elvitegravir/r or the reverse ( n=7 per sequence), all under fed conditions. Elvitegravir, ritonavir and etravirine pharmacokinetics were determined on days 10 and 20 using non-compartmental analyses. Lack of pharmacokinetic alteration bounds for 90% confidence intervals (CI) about the geometric mean ratio (GMR; coadministration versus alone) were 70–143% for elvitegravir and ritonavir pharmacokinetics (maximum concentration [Cmax], concentration at the end of the dosing interval [Ctau] and area under the plasma concentration–time curve [AUCtau; 0–24 h] and 80–125% for etravirine pharmacokinetics (AUCtau 0–12 h).

Results

Of the 34 enrolled participants, 31 completed the study. There were three discontinuations, but none were caused by adverse events (AEs). The most common treatment-emergent AE was headache. Elvitegravir pharmacokinetic GMR was 6–7% higher following elvitegravir/r plus etravirine dosing versus elvitegravir/r. The GMR for etravirine and ritonavir AUCtau were 2.4% and 12.3% lower, respectively. Importantly, the 90% CI for elvitegravir and etravirine pharmacokinetics and AUCtau and Cmax for ritonavir were within the lack of alteration bounds.

Conclusions

Elvitegravir/r and etravirine do not undergo clinically relevant drug interactions and can be coadministered without dose adjustment.

Etravirine: a second-generation NNRTI for treatment-experienced adults with resistant HIV-1 infection

Etravirine, a second-generation non-nucleoside reverse transcriptase inhibitor (NNRTI), was approved in the USA in January, 2008, with approval in Europe expected later this year. It is dosed at 200 mg (two 100 mg tablets) twice daily foll owing a meal. It is approved for treatment of HIV-1 infection in adults failing a stable antiretroviral regimen with resistance to other NNRTIs and other antiretroviral agents. Etravirine is active against HIV with single mutations in the reverse transcriptase (e.g., K103N) that confer class resistance to first-generation NNRTIs. Clinical efficacy in Phase III trials has been demonstrated for up to 48 weeks of follow-up. In these Phase III trials, rash was the only adverse event that was significantly more prevalent with etravirine than with placebo. Etravirine has a tolerability and safety profile comparable to placebo with the exception of rash. Rash was generally grade 1 or 2, was not associated with prior NNRTI-related rash, was more common in women than in men, appeared a median of 12 days after treatment initiation and resolved spontaneously with continued therapy. Etravirine is the first agent in the NNRTI class that can be used for HIV-1 virus with resistance to other NNRTIs owing to a higher genetic barrier to resistance.

Broad Advances in Understanding HIV Resistance to Antiretrovirals: Report on the XVII International HIV Drug Resistance Workshop

The 2008 International HIV Drug Resistance Workshop explored six topics on viral resistance: new antiretrovirals; clinical implications; epidemiology; new technologies and interpretations; HIV pathogenesis, fitness, and resistance; and mechanisms of resistance. The last of these topics provided a forum for new work on resistance of hepatitis B and C viruses, which were also explored in two poster sessions. Much work focused on resistance to the two most recent antiretroviral classes (integrase inhibitors and CCR5 antagonists), a new set of entry inhibitor candidates and one new class represented by the maturation inhibitor bevirimat. Other research explored two novel non-nucleoside reverse transcriptase inhibitors, etravirine and IDX899. Epidemiological work analysed rates of transmitted resistant virus, multiclass resistance in antiretroviral-experienced patients and a heightened resistance risk in injecting drug users regardless of adherence. New research on resistance technologies involved an enhanced assay for HIV-1 coreceptor determination and improved gene-based tools for predicting coreceptor use. In the pathogenesis arena, a small study of intensification shed light on the likely source of residual viraemia in patients on successful antiretro-viral therapy. A large study in Mozambique correlated the timing of infant infection with selection, transmission and persistence of nevirapine resistance mutations. Mechanistic research explored resistance to the integrase inhibitor raltegravir, K65R-mediated resistance to tenofovir and the role of connection domain mutations in resistance to zidovudine.

Maraviroc, risks and benefits: a review of the clinical literature

BACKGROUND

Maraviroc represents the first licensed CCR5 co-receptor antagonist from the new antiretroviral (ARV) drug-class of entry inhibitors.

RESULTS

Results of Phase III clinical trials in three-drug-class experienced patients have presented maraviroc as a promising new agent for treatment of HIV-1-infection. Maraviroc (b.i.d./q.d.) + optimised background therapy (OBT) provided significantly superior virological control and CD4+ increases compared with placebo + OBT at 48 weeks, with no clinically relevant differences in the safety profile between the maraviroc and the placebo groups.

CONCLUSION

Its proven efficacy in cases of virological failure and three-class ARV-drug resistance is a major benefit of maraviroc compared to the so far commercially available drugs from existing (non-) nucleoside reverse transcriptase inhibitors ([N]NRTI) and protease inhibitors drug-classes, particularly in times of increasing ARV drug resistance. Moreover, the tolerability profile of the drug makes maraviroc particularly appealing as a combination partner in ARV therapy. As maraviroc however is only effective against CCR5-tropic HIV-1, tropism testing is required before initiation of treatment. Tropism-testing possibilities are still limited, and presently only possible at high costs. The main constraints to be considered in the clinical use of maraviroc are the declining number of CCR5-tropic patients with advanced HIV-1 disease owing to tropism-shifting and the occurrence of drug-drug interactions, requiring regular dose adaptations. The true clinical value of this new substance and its future role in the treatment of HIV-1-infection remains to be defined by further data from clinical studies and by future experiences of practitioners.

[Rational use of modern substances for the treatment of HIV-infection]

Treatment options for HIV-infection have been improved significantly. Drugs with new modes of action have been licensed (integrase inhibitor and CCR5-inhibitor) as well as drugs within the existing classes, but improved activity in case of resistance (e.g. darunavir, tipranavir, etravirin). The treatment goal today is complete and durable suppression of viral replication in treatment-naïve as well as pre-treated patients. The significance of new drugs in the clinical setting will be defined more precisely in the near future, as all new substances have been licensed for pre-treated patients only so far.