Dual nucleoside analogue treatment in the era of highly active antiretroviral therapy (HAART): a single-centre cross-sectional survey

Roberto Manfredi,*, Leonardo Calza and Francesco Chiodo

Department of Clinical and Experimental Medicine, Division of Infectious Diseases, University of Bologna, S. Orsola Hospital, Via Massarenti 11, I-40138 Bologna, Italy


    Abstract
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Since limited literature exists regarding the outcomes of dual nucleoside analogue reverse transcriptase inhibitor (NRTI) treatment in the highly active antiretroviral therapy (HAART) era, a cross-sectional survey was carried out in a population of around 1000 HIV-infected patients in a single northern Italian university hospital, to assess the frequency, background and long-term evolution of anti-HIV treatment conducted with two NRTIs. An appreciable proportion (20.4%) of the 798 HIV-infected patients currently treated with antiretrovirals at our centre still take a dual NRTI combination, and the great majority of them (68.7%) have a stable disease course (characterized by a viral load <3.7 log10 HIV RNA copies/mL, a maintained CD4+ lymphocyte count and absence of HIV disease progression after at least 24 months of follow-up), regardless of the selected regimen, prior antiretroviral therapy use, and baseline virological and immunological situation. Further studies are warranted to establish whether dual NRTI regimens may have residual indications in the HAART era, and whether the shift to a triple antiretroviral combination is expected to lead to long-term advantages in patients with a low risk of disease progression while on dual NRTI treatment.


    Introduction
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Since the widespread introduction of highly active antiretroviral therapy (HAART; usually defined as three active agents of one or two classes) in 1996, there is no apparent need for the use of isolated dual nucleoside analogue reverse transcriptase inhibitor (NRTI) combinations, which appear significantly less potent and durable compared with a triple therapy containing protease inhibitors or non-nucleoside reverse transcriptase inhibitors in patients with a detectable viral load and immune system abnormalities.13 Consequently, very limited controlled data have become available since 19974,5 with respect to patients who started or continued treatment with nucleoside analogues because of a comparably low plasma viral load and a moderate to absent concurrent immunodeficiency.1,6,7 In particular, data from the Delta trial analysed retrospectively by Flandre6 showed that a viral load <3.0 log10 HIV RNA copies/mL was maintained for at least 48 weeks by all the 83 patients receiving dual NRTI treatment (zidovudine plus didanosine or zalcitabine). This result was related to a baseline viraemia <4.0 log10 and an initial CD4+ count >200 cells/µL. Later, Morlat et al.7 reported a prospective cohort study of 130 antiretroviral-naive patients with a CD4+ lymphocyte count >350 cells/µL who were treated favourably with a combination of two nucleoside analogues in the period 1996–1998; a lower viraemia at initiation of dual NRTI therapy was significantly associated with complete viral suppression maintained after 1 year.

A broad range of reasons suggests the continuation of successful dual NRTI combination in everyday clinical practice.6,7 Therefore, we performed a cross-sectional survey in order to assess the frequency, background and long-term evolution of anti-HIV treatment conducted with dual NRTI in a population of around 1000 HIV-infected patients referring to a single tertiary care centre in northern Italy.


    Patients and methods
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Of 968 patients currently treated with antiretrovirals at our centre, 798 were eligible for the present study by the critera that they had not had their anti-HIV drugs changed during the previous 6 months, had appropriate virological and immunological assessment performed at least at quarterly intervals, and had an appropriate (>=90%) adherence to antiretroviral therapy (as checked by monthly direct drug distribution and accountability performed at our outpatient service). Failure of dual NRTI antiretroviral regimen occurring within the previous 6 months did not represent an exclusion criterion.

Plasma HIV RNA levels were assessed by three highly sensitive techniques (a reverse transcriptase PCR, a NASBA assay or a branched-DNA test), with undetectable levels ranging from 40 to 200 copies/mL (<2 log10). Clinical staging was assessed on the grounds of the 1993 CDC classification.8 Genotypic resistance testing (carried out with an open gene automated DNA sequencing system supplied by Visible Genetics Inc., Toronto, Ontario, Canada) was performed throughout the follow-up, when this testing became available (i.e. mid-1999), when plasma viral load was above 3.7 log10 HIV RNA copies/mL.

Statistical analysis was carried out by Student's t-test, Mantel-Haenszel {chi}2 test, or Fisher's exact test where applicable, with significance levels set at P < 0.05.


    Results
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
As of September 2000, 163 of the 798 evaluable patients (20.4%) who had received consistent antiretroviral therapy for at least 6 months were treated with dual NRTI: 120 were at CDC disease stage A, 29 at stage B, and the remaining 14 subjects were at disease stage C. Among these patients, the leading drug combination was lamivudine plus stavudine (82 of 163 cases, 50.3%), followed by zidovudine–lamivudine (41 cases, 25.2%), didanosine–stavudine (32 cases, 19.6%), zidovudine–didanosine (six cases, 3.7%), and zidovudine–zalcitabine (two cases, 1.2%). Most of the patients (127 of 163, 77.9%) began their treatment with nucleoside analogue monotherapy (59 cases, 36.2%) or dual treatment (68 cases, 41.7%), while the remaining 36 patients had previously been treated with a triple combination, but declined the adjunct of a third anti-HIV compound (other than nucleoside analogues) after experiencing adverse events due to protease inhibitors (31 cases, 19%) or non-nucleoside reverse transcriptase inhibitors (five cases, 3.1%). On the whole, the current dual NRTI combination had been taken for between 6 and 44 consecutive months (mean 24.9 ± 10.1 months). When initiating this last nucleoside analogue association, 59 patients (36.2%) were naive to antiretrovirals, while the remaining 104 had received prior antiretroviral treatment (administered for 6–69 months; mean 21.5 ± 14.1 months). At the time of start of the current dual NRTI therapy, mean plasma HIV RNA level was 3.8 ± 0.8 log10 copies/mL (range undetectable to 4.8 log10 copies/mL) in the 156 patients of the 163 who had this determination done, while mean CD4+ lymphocyte count was 368.8 ± 101.2 cells/µL (range 235–768 cells/µL).

During the subsequent follow-up (24.2 ± 7.1 months on average, ranging from 6 to 44 months), nearly 70% of the patients examined (113 of 163) had a plasma viral load persistently ranging from undetectable levels to 3.7 log10 copies/mL (5000 copies/mL), and did not experience a rise of viremia >1.0 log10 at any time throughout their treatment with dual NRTI. These results occurred regardless of the different nucleoside analogue combination used (including use of lamivudine), baseline viral load, initial CD4+ cell count and prior antiretroviral experiences (data not shown). Of the remaining 50 patients, 31 subjects presented a history of at least one peak plasma HIV RNA assay ranging from >3.7 to 4.3 log10 HIV RNA copies/mL while treated with dual NRTIs, whereas the remaining 19 subjects had >4.3 log10 HIV RNA copies/mL at least once. All these patients declined to commence or re-introduce a triple antiretroviral regimen, including a protease inhibitor or a non-nucleoside reverse transcriptase inhibitor, even though it was repeatedly advised based on international guidelines for antiretroviral therapy.3 A genotyping resistance assay was available for 27 of these last 31 subjects, and showed an appreciable frequency of mutations involving mostly codons 184 (25.9%), 215 (22.2%) and 41 (14.8%). A remarkable immunological deterioration (i.e. a drop of CD4+ lymphocyte count >150 cells/µL or >20% compared with baseline levels) occurred in only 32 of 163 cases (19.6%), all but one belonging to the patient group with a history of viraemia exceeding 3.7 log10 HIV RNA copies/mL at least once (P < 0.0001 versus the remaining 113 patients).

No cases of newly recognized AIDS diagnoses or deaths were detected during the whole study period.


    Discussion
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Our experience is clearly limited by its characteristics of single-centre, uncontrolled, observational survey of a cohort including both antiretroviral-naive and -experienced patients with varying baseline virological and immunological features. According to this study, an appreciable proportion (slightly more than 20%) of patients currently treated at our outpatient centre still takes a dual NRTI combination, and the great majority of them (68.7%) have a stable disease course (characterized by a viral load <3.7 log10 HIV RNA copies/mL, a satisfactory CD4+ lymphocyte count, and absence of signs and symptoms of HIV disease progression after 24 months of mean follow-up), irrespective of the selected regimen, prior antiretroviral therapy use and baseline surrogate markers.

When considering the 50 remaining patients, who experienced some virological (with or without immunological) failure, the frequent refusal by patients of the recommended triple drug regimens (occurring in 38% of these cases) is noteworthy, as is the contained frequency of genotypic mutations conferring resistance to one or more nucleoside analogues (with that involving the 184 codon occurring in >25% of evaluated patients with a viral load >3.7 log10 HIV-RNA copies/mL).

Despite the fact that our cross-sectional survey included a great number of subjects who were already experienced in antiretroviral therapy (63.8% of cases), a more favourable overall outcome was seen compared with that of previous studies reported in antiretroviral-naive individuals followed up for a shorter time than our patients.1,6,7 The reason for this different response is probably related to a significantly lower mean baseline viral load in our series (<104 log10 copies/mL). In particular, in a report early in the HAART era, Rhone et al.1 treated 245 antiretroviral-naive subjects with a mean baseline viral load of 58 000 copies/mL (using zidovudine–lamivudine in 63% of cases and stavudine–lamivudine in 19%) and observed a 39% rate of viral suppression (i.e. a plasma viral load <500 copies/mL) soon after treatment introduction; this success rate decreased to 13% when subjects who had at least two laboratory examinations available were considered.1

Later, Flandre6 reported a 48 week follow-up of 591 treatment-naive patients with an initial mean viraemia of 4.7 log10 copies/mL treated with zidovudine combined with either didanosine or zalcitabine: in 83 cases (14%) a viral load <3.0 log10 was maintained throughout the follow-up, and the therapeutic response proved significantly related to a better initial virological and immunological situation compared with that of patients failing dual NRTI.6

Finally, in contrast to our patient series, individuals enrolled in the Aquitaine cohort study7 had a greater initial median viraemia (4.52 log10 copies/mL) and a higher baseline CD4+ count (466 cells/µL), while a comparable baseline disease staging was observed. Surprisingly, French patients received a less effective and durable nucleoside analogue combination (i.e. zidovudine plus zalcitabine)4,5,9 as the most frequent regimen (38% of cases, compared with 1.2% in our series), while only 5% of patients were treated with lamivudine plus stavudine (compared with over 50% of cases treated in our centre). During the evaluable follow-up time (median 12 months, ranging from 1 day to 26 months), an apparently limited mean virological gain was obtained (–1.6 log10), especially when compared with baseline viraemia. Since 45% of patients reached a viral load <500 copies/mL, and in 70% of cases overall a viral load <5000 copies/mL was attained, at least 30% of patients were expected to suffer from an evident virological failure. In fact, at an extended follow-up analysis (median 28 months), only 18 of the 55 patients who remained evaluable had a viral load <500 copies/mL, and 40% of these subjects had switched to a triple anti-HIV therapy, although their follow-up was still considered evaluable by the authors.7 Overall, 33% of enrolled patients changed their initial dual NRTI therapy during their first year of follow-up, and nearly 8% of patients switched to a triple regimen. Finally, although 96% of patients maintained a CD4+ count >350 cells/µL throughout the study period, clinical deterioration occurred more frequently compared with our experience: three patients developed AIDS and one died.7 Compared with our experience, not all quoted literature studies1,6,7 gave the frequency of double nucleoside use in an unselected patient population and excluded previously experienced subjects, while they did include patients with a comparatively higher initial viral load (and therefore prone to experience failure after an isolated double therapy) and pointed out a significant relationship between therapeutic response and a significantly lower initial viraemia (a viral load <10 000 copies/mL in the Aquitaine study),7 but failed to identify a threshold value of viraemia that had a significant predictive value of a satisfactory and sustained response to a dual NRTI therapy. As in our series, no significant difference was noticed when stratifying data according to the different possible nucleoside analogue associations.1,6,7

Until the year 2000, antiretroviral therapy ‘in the real world' seemed to allow a persistent recourse to, or maintenance of, dual NRTI combinations, either in patients with a stable clinical and laboratory picture (who do not seem to need a triple combination), or in subjects who voluntarily refuse regimens containing more than two drugs (especially when poor compliance or toxicity with protease inhibitors and non-nucleoside reverse transcriptase inhibitors are of concern). Our experience underlines the fact that dual NRTI associations may represent a continuing therapeutic option for patients with viral load levels not exceeding 104 copies/mL and a CD4+ cell count of at least 300–350 cells/µL, since it seems to ensure a stable virological, immunological and clinical disease evolution after at least 2 years of follow-up. Controlled studies are therefore warranted to establish whether the shift to a triple antiretroviral combination will lead to a real long-term advantage in patients with a stable disease while on a dual NRTI therapy, or whether dual NRTI therapy itself may significantly affect long-term HIV disease course (compared with a deferred treatment initiation) in patients with such a favourable baseline virological and immunological situation.2,10,11 In fact, the great majority of controlled data confirmed the benefit of early HAART introduction in patients with a CD4+ count <350 cells/µL and/or an appreciable plasma viral load (at least 3.7–4.0 log10 HIV RNA copies/mL).2,3,11 Dual NRTI combinations are known to compare favourably with all triple drug regimens in terms of toxicity, drug–drug interactions, patient adherence and comprehensive costs.2,4,6,1113 Therefore, they might have residual indications as an initial antiretroviral strategy, sparing the most effective anti-HIV compounds (protease inhibitors and non-nucleoside reverse transcriptase inhibitors) for patients with a very low risk of disease progression who are prone to undergo a close surveillance of laboratory markers of HIV disease progression and viral resistance profile. In fact, the major drawback of dual NRTI therapy is the failure to obtain a complete and sustained suppression of viraemia, and the consequent increased risk of viral resistance.1,2,11,14,15


    Notes
 
* Corresponding author. Tel: +39-051-63-63-355; Fax: +39-051-34-35-00; E-mail: manfredi{at}med.unibo.it Back


    References
 Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
1 . Rhone, S. A., Hogg, R. S., Yip, B., Sherlock, C., Conway, B., Schecther M. T. et al. (1998). Do dual nucleoside regimens have a role in an era of plasma viral load-driven antiretroviral therapy? Journal of Infectious Diseases 178, 662–8.[ISI][Medline]

2 . Hirschel, B. & Opravil, M. (1999). The year in review: antiretroviral treatment. AIDS 13, Suppl. A, A177–87.

3 . Carpenter, C. C. J., Cooper, D. A., Fischl, M. A., Gatell, J. M., Gazzard, B. G., Hammer, S. M. et al. (2000). Antiretroviral therapy in adults. Updated recommendations of the International AIDS Society—USA Panel. Journal of the American Medical Association 283, 381–90.[Abstract/Free Full Text]

4 . Delta Coordinating Committee. (1996). Delta: a randomized double blind controlled trial comparing combinations of zidovudine plus didanosine or zalcitabine with zidovudine alone in HIV-infected individuals. Lancet 348, 283–91.[ISI][Medline]

5 . Staszewski, S., Hill, A. M., Bartlett, J., Eron, J. J., Katlama, C., Johnson, J. et al. (1997) Reductions in HIV-1 disease progression for zidovudine/lamivudine relative to control treatments: a meta-analysis of controlled trials. AIDS 11, 477–83.[ISI][Medline]

6 . Flandre, P. on behalf of the Delta Coordinating Committee. (1999). Patients with HIV-1 RNA below 1000 copies/mL after 48 weeks on dual nucleoside analogue combination therapies. AIDS 13, 430–1.[ISI][Medline]

7 . Morlat, P., Marimotou, C., Dequae-Merchadou, L., Pellegrin, I., Mercie, P., Neau, D. et al. (2000). Dual nucleoside regimens in nonadvanced HIV infection: prospective follow-up of 130 patients, Aquitaine Cohort, 1996 to 1998. Journal of Acquired Immune Deficiency Syndromes 23, 255–60.[ISI][Medline]

8 . Centers for Disease Control and Prevention. (1992). 1993 revised classification system for HIV infection and expanded surveillance case definition for AIDS among adolescents and adults. Morbidity and Mortality Weekly Report 41, 1–19.

9 . Molina, J. M., Chêne, G., Ferchal, F., Journot, V., Pellegrin, I., Sombardier, M. N. et al. (1999). The Albi trial: a randomized controlled trial comparing stavudine plus didanosine with zidovudine plus lamivudine and regimen alternating both combinations in previously untreated patients infected with human immunodeficiency virus. Journal of Infectious Diseases 180, 351–8.[ISI][Medline]

10 . Levy, J. A. (1998). Caution: should we be treating HIV infection early? Lancet 352, 982–3.[ISI][Medline]

11 . Harrington, M. & Carpenter, C. C. (2000). Hit HIV-1 hard, but only when necessary. Lancet 355, 2147–52.[ISI][Medline]

12 . Fäktenheuer, G., Theisen, A., Rockstroh, J., Leutner, C., Sauerbruch, T. & Spengler, U. (1997).Virological treatment failure of protease inhibitor therapy in an unselected cohort of HIV-infected patients. AIDS 11, 113–6.[ISI][Medline]

13 . Carr, A., Samaras, K., Burton, S., Law, M., Freund, J., Chisholm, D. J. et al. (1998). A syndrome of peripheral lipodystrophy, hyperlipidemia and insulin resistance in patients receiving HIV protease inhibitors. AIDS 12, 51–8.

14 . Raboud, J. M., Montaner, J. S., Conway, B., Rae, S., Reiss, P., Vella, S. et al. (1998). Suppression of plasma viral load below 20 copies/ml is required to achieve a long-term response to therapy. AIDS 12, 1619–24.[ISI][Medline]

15 . Pillay, D., Taylor, S. & Richman, D. D. (2000). Incidence and impact of resistance against approved antiretroviral drugs. Review of Medical Virology 10, 231–53.[ISI][Medline]

Received 23 November 2000; returned 27 February 2001; revised 20 March 2001; accepted 21 May 2001