BMJ  2004;328:249 (31 January), doi:10.1136/bmj.37995.435787.A6 (published 23 January 2004)

Paper

Clinical efficacy of antiretroviral combination therapy based on protease inhibitors or non-nucleoside analogue reverse transcriptase inhibitors: indirect comparison of controlled trials

¹ Service Universitaire des Maladies Infectieuses et du Voyageur, Centre Hospitalier de Tourcoing, Faculté de Médecine de Lille, BP 619, F 59208 Tourcoing, France, ² Department of Social Medicine, University of Bristol, Bristol BS8 2PR, ³ Department of Social and Preventive Medicine, University of Bern, Switzerland, ⁴ INSERM U593, Bordeaux, France

Abstract

Objective To compare the clinical efficacy of triple antiretroviral regimens based on protease inhibitors and non-nucleoside analogue reverse transcriptase inhibitors (NNRTIs) in adults positive for antibodies to HIV-1.

Design Systematic review and meta-analysis using indirect comparisons of clinical trials comparing three drug regimens based on two nucleoside reverse transcriptase inhibitors (NRTIs) and either a protease inhibitor or an NNRTI with two drug regimens (two NRTIs). Participants had no previous exposure to protease inhibitors or NNRTIs.

Data sources Medline, the Cochrane controlled trials register, Aidstrials, Aidsdrugs, conference proceedings, and trial registers.

Main outcome measure Progression to AIDS or death.

Results 14 trials, totalling 6785 patients, were identified. Most patients had been exposed to an NRTI and had advanced immunodeficiency at baseline; 1096 progressed to AIDS or died. Seven trials assessed protease inhibitors based triple regimens and seven assessed NNRTI based triple regimens (nevirapine or delavirdine). Triple therapy was more effective than dual therapy. The effect was pronounced for protease inhibitor based regimens (odds ratio 0.49, 95% confidence interval 0.41 to 0.58) but non-significant for NNRTI based regimens (0.90, 0.71 to 1.15). Indirect comparison of the two regimens gave an odds ratio of 0.54 (0.49 to 0.73) in favour of protease inhibitor based treatments. Increases in CD4 cell counts were smaller and suppression of viral replication less with NNRTI based regimens.

Conclusions Indirect evidence shows that protease inhibitor based triple regimens are superior to regimens based on the NNRTIs nevirapine and delavirdine in patients with advanced immunodeficiency who have been exposed to NRTIs. Large trials with clinical end points are required.

Introduction

The introduction in industrialised countries of highly active antiretroviral therapy—a combination of three drugs including either a protease inhibitor or a non-nucleoside analogue reverse transcriptase inhibitor (NNRTI) and two nucleoside analogue reverse transcriptase inhibitors (NRTIs)—led to a dramatic decline in morbidity and mortality among patients infected with HIV-1.^1-3 Many different combinations of highly active antiretroviral therapy regimens are available, some of which differ in toxicity, adverse events, their ability to suppress viral replication, the development of viral resistance, and patient adherence.^4-7

No randomised clinical trials have compared the clinical effectiveness of protease inhibitor based and NNRTI based combination therapies. Thus it is unclear whether there are relevant differences between the regimens in preventing clinical progression to AIDS or death. In trials comparing highly active antiretroviral therapy regimens, the low rate of disease progression made it impractical to use clinical events as primary end points. Trials exclusively reporting surrogate endpoint data, however, have to be interpreted with caution.^{8 9}

We performed indirect comparisons between triple regimens based on protease inhibitors and NNRTIs by using clinical and surrogate endpoint data from randomised controlled trials comparing triple regimens with dual regimens.

Methods

Using Cochrane methods we searched Medline, the Cochrane controlled trials register, Aidstrials, and Aidsdrugs for randomised clinical trials of antiretroviral therapy in patients infected with HIV-1 published from January 1994 to December 2000.¹⁰ We also hand searched reference lists, reviews, and abstracts from major conferences and consulted the French Arcat Sida register, the European database on AIDS and HIV infection, and the database of the US Community Programs for Clinical Research on AIDS. Finally, we contacted experts and pharmaceutical companies.

Inclusion criteria, data abstraction, and outcomes
We included randomised controlled studies published in any language if they reported on clinical end points and enrolled patients who were HIV-1 positive, aged 16 years or older, and had not received protease inhibitors or NNRTIs. We were interested in triple antiretroviral therapy compared with dual therapy based on recommended antiretroviral agents.^{11 12} Dual therapy was defined as a combination of two NRTIs and triple therapy as two NRTIs combined with a protease inhibitor or an NNRTI.

The primary outcome was progression to a new AIDS defining disease or death.¹³ Additional outcomes included the CD4 cell count, plasma HIV-1 RNA concentration, and the proportion of patients reaching plasma HIV-1 RNA concentrations of less than 500 copies/ml at the end of follow up. We assessed the methodological quality of trials on the basis of adequacy of concealment of patients' allocation to treatment group and blinding to placebo.¹⁴

Statistical analysis
Data on clinical progression and suppression of viral replication were based on intention to treat analysis. We calculated odds ratios with 95% confidence intervals, comparing the probability of clinical progression and the probability of reaching HIV-1 RNA concentrations below 500 copies/ml between patients receiving triple antiretroviral therapy and those receiving dual therapy.

We used random effects models to combine results on the odds ratio or weighted mean difference scales. The degree of between trial heterogeneity was measured by the additive between trial variance (²). Publication bias was assessed by funnel plot. Crude and adjusted indirect comparisons were performed by fitting random effects meta-regression models. Variables entered in the model are detailed on bmj.com.

Results

We identified 14 trials that met our inclusion criteria (see bmj.com). The 14 trials totalled 6785 patients (table). Nine trials described adequate concealment of allocation and 12 used placebos to blind patients and caregivers.

View this table: [in this window] [in a new window]   Characteristics of 14 randomised controlled trials comparing protease inhibitor based triple therapy and non-nucleoside analogue reverse transcriptase inhibitor (NNRTI) based triple regimens with dual therapy

 

Clinical progression
Clinical progression occurred in 445 of 3392 patients (13.1%) receiving triple therapy and 651 of 3393 (19.2%) patients receiving dual therapy (fig 1; combined odds ratio 0.65 (95% confidence interval 0.52 to 0.81)). Heterogeneity was evident between trials, with odds ratios ranging from 0.32 to 1.31 (² = 0.073, test of heterogeneity P = 0.090).

View larger version (51K): [in this window] [in a new window]   Fig 1 Meta-analysis of randomised controlled trials comparing effect of triple antiretroviral regimens with dual regimens on progression to AIDS or death, stratified by type of triple regimen

 

In univariate meta-regression analysis, protease inhibitor based triple regimens showed larger treatment effects than those based on NNRTIs (P < 0.0001), triple regimens including didanosine showed smaller treatment effects than those without didanosine (P < 0.0001), and trials that enrolled a larger proportion of patients with AIDS tended to show larger differences in treatment effects between triple and dual regimens (P = 0.067). These variables were responsible for the between trial heterogeneity. We found little evidence for an association with other variables entered in the model, including length of follow up, year of publication of the trial, publication in full or as abstract only, median age of study populations at baseline, whether patients were NRTI naive or not, and CD4 cell count and viral load at baseline. Finally, there was little evidence that the censoring strategy (follow up censored at virological failure or not) or the quality of trials influenced results, and little evidence of funnel plot asymmetry.

When triple regimens were compared with dual regimens the odds ratio for clinical progression was 0.49 (0.41 to 0.58) for a protease inhibitor based regimen but 0.90 (0.71 to 1.15) for an NNRTI based regimen. The crude odds ratio from the indirect comparison was 0.54 (0.40 to 0.73). This changed little when adjusted for whether or not the regimen included didanosine, for the proportion of study participants with AIDS, or for both variables, although adjustments resulted in odds ratios with wide confidence intervals which included 1 (fig 2). When trials were excluded that examined saquinavir hard gel, which is no longer used, or the NNRTI delavirdine, which is not widely used, the protease inhibitor based triple regimens continued to show larger treatment effects than the NNRTI based regimens (0.54, 0.37 to 0.77).

View larger version (29K): [in this window] [in a new window]   Fig 2 Comparisons from meta-analysis of randomised controlled trials comparing the effects of triple antiretroviral regimens with dual regimens on risk of progression to AIDS or death

 

Differences in CD4 cell count and plasma HIV-1 RNA concentration
Eleven studies could be included in the analysis of CD4 cell counts. Compared with dual regimens, triple regimens led to a superior CD4 cell response (pooled difference in CD4 cell count, 40 (19 to 60) cells/µl; see also bmj.com). An indirect comparison showed an additional increase of 25 (-17 to 68) CD4 cells/µl with protease inhibitor based regimens when compared with NNRTI based regimens. Triple therapy was also superior to dual therapy, resulting in an estimated additional reduction of HIV-1 RNA concentrations of 0.56 (0.92 to 0.19) log copies/ml. The odds ratio for achieving a viral load below 500 copies/ml with triple compared with dual therapy was 9.6 (4.4 to 21.0). Again, the indirect comparison showed an additional reduction of HIV RNA concentration of -0.59 (-1.32 to 0.15) log copies/ml with protease inhibitor regimens compared with NNRTI based regimens. The odds ratio for reaching an undetectable viral load was 6.0 (2.2 to 16.6).

Discussion

Triple antiretroviral therapy is superior to dual therapy for preventing progression to AIDS or death in patients with advanced disease who have been exposed to NRTIs. Surprisingly, we found large variation between the results of the included trials. This was largely explained by the drug classes used in triple regimens: those containing protease inhibitors were clearly superior to dual regimens but this was not the case for triple regimens based on the NNRTIs nevirapine and delavirdine. Indirect comparisons indicated that the risk of clinical progression was reduced by 40-50% with protease inhibitor based regimens. In line with these findings, we found smaller increases in CD4 cell counts and less pronounced suppression of viral replication with the NNRTI based regimens.

What is already known on this topic Randomised clinical trials have strongly supported triple antiretroviral regimens in HIV infected patients No trials have compared the clinical effectiveness of protease inhibitor regimens with non-nucleoside reverse transcriptase inhibitor (NNRTI) regimens In the absence of such trials, indirect comparisons can provide useful information What this study adds Indirect comparisons suggest that triple regimens with protease inhibitors are superior to those with the NNRTIs nevirapine or delavirdine in patients with advanced disease who have used nucleoside reverse transcriptase inhibitors In the absence of large trials directly comparing these regimens these results are relevant to current antiretroviral therapy, particularly in settings where resistance testing is not widely available

Strengths and limitations
No data from direct randomised comparisons of the clinical efficacy of different triple antiretroviral regimens exist. Our systematic review is based on 6785 patients, 1096 of whom progressed to AIDS or died, from trials comparing triple regimens with dual regimens. This represents a large evidence base, suitable for indirect comparisons of the clinical effectiveness of the antiretroviral regimens. Such comparisons were appropriate because the trials were of high methodological quality.

Our findings should, however, be interpreted with caution. Firstly, the finding of superior efficacy of protease inhibitor based regimens by indirect comparison is observational and therefore vulnerable to bias. Baseline characteristics of the participants were heterogeneous in both groups, with large variations in the proportion of patients with AIDS, the median CD4 cell count, and viral load. Furthermore, didanosine was more often used with NNRTIs than with protease inhibitors. When we adjusted for these differences in meta-regression models, the coefficients were not noticeably altered. We acknowledge that we could only adjust for information that was aggregated at the trial level. Individual patient data would have been preferable but were not available. Indirect comparisons adjusted at the aggregate level usually agree with direct comparisons.¹⁵ Finally, the smaller gains in CD4 cell counts and less pronounced suppression of viral replication with NNRTI based triple regimens support the finding of higher progression rates.

Our results are limited to the regimens and patient populations of the included studies—for example, the NNRTI efavirenz was not included in the triple regimens. The trials involving efavirenz that we identified did not assess clinical end points and had to be excluded. Several observational cohort studies have shown efavirenz to be more efficacious than nevirapine.^16-18 However, the recent 2NN trial, which directly compared these two drugs in antiretroviral naive patients showed that they did not differ in their ability to suppress viral replication.¹⁹ Furthermore, most of the patients enrolled in the trials in our meta-analysis used NRTIs. Thus, it is not possible to extrapolate these results to HIV-1 infected patients who have never used antiretroviral drugs, a population in which NNRTI based regimens are widely used. It may be postulated that due to cross resistance, patients who have previously undergone prolonged therapy with NRTIs would be resistant to all drugs in the NRTI class. In this situation, a regimen containing one protease inhibitor and two NRTIs could be more effective than a regimen based on one NNRTI and two NRTIs because the genetic barrier to resistance is greater with protease inhibitors.²⁰

Our results provide important information for clinical practice, and may be especially relevant for doctors working in countries where resistance testing is not generally available. In these countries, patients tend to be at an advanced stage when starting therapy and, particularly in urban settings, a proportion will have been exposed to NRTI monotherapy or dual therapy.²¹

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This is the abridged version of an article that was posted on bmj.com on 23 January 2004: http://bmj.com/cgi/doi/10.1136/bmj.37995.435787.A6

Editorial by Loewenson and McCoy and Education and debate p 280

Contributors: See bmj.com

Funding: None.

Competing interests: YY has received travel grants from various pharmaceutical companies including Aventis, Boehringer Ingelhem, Bristol-Myers Squibb, Gilead Sciences, GlaxoSmithKline, Pfizer, Roche, and Schering Plough. He has received honorariums for presentation at workshops and consultancy honorariums from Boehringer Ingelheim, Bristol-Myers Squibb, GlaxoSmithKline, and Pfizer. ME has received travel grants, grants, or honorariums from Boehringer Ingelheim, Bristol-Myers-Squibb, and GlaxoSmithKline. YM has received travel grants, grants, or honorariums from Abbott, Aventis, Boehringer Ingelheim, Bristol-Myers Squibb, Gilead Sciences, GlaxoSmithKline, Merck Sharp and Dohme, Pfizer, Roche, and Schering. GC has received consultancy honorariums from Aventis, Bristol-Myers Squibb, Gilead Sciences, GlaxoSmith-Kline, and Roche.

Ethical approval: None required.

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(Accepted 6 January 2004)

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