Disease Progression, Adherence, and Response to Protease Inhibitor Therapy for HIV Infection in an Urban Veterans Affairs Medical Center

Summary : Indinavir therapy has demonstrated promise in the treatment of HIV-1 infection in clinical trials; however, its efficacy in a U.S. Veterans Affairs Medical Center, where access to therapy is generally unimpeded, is unknown. A review of the Miami cohort was conducted for the year beginning May 1996 to evaluate response to indinavir plus two nucleoside analogues. Of 483 HIV-1-positive patients (97% male; mean age, 46.7 ± 9.7 years), 266 were offered indinavir based on their having CD4 counts <200 cells/μl or viral loads >10,000 copies/ml. Of these patients, 36% were adherent and experienced significant reductions in viral loads (-93,325 ± 147,911 copies/ml) and elevations in CD4⁺ (111 ± 103 cells/μl) and CD8⁺ (225 ± 338 cells/μl) T cell counts. Adherent patients with baseline CD4 counts <100 cells/μl were 4.5 times more likely to have follow-up viral loads >10,000 copies/ml than those with CD4 >200 cells/μl. Adherent patients with CD4 counts <100 cells/μl did not show evidence of immune exhaustion because they were equal to those with CD4 counts >200 cells/μl in their capacity to replenish CD4 cells. Nonadherence to the regimen resulted in loss of therapeutic benefit and suggested that strategies to enhance adherence may become an essential component of treatment.

Protease inhibitor (PI) therapy for treatment of HIV-1 has demonstrated promise in lowering viral burden and limiting disease progression ^(1-3). These agents act by inhibiting viral maturation and thereby prevent formation of infectious virions ^(4-8). When coupled with the nucleoside reverse transcriptase inhibitors (NRTIs), they provide an effective level of viral suppression that has been termed highly active antiretroviral therapy (HAART). Although this therapy has demonstrated promise in clinical trials ^(9-12), its efficacy in actual clinical practice has not been determined. In this study, the response to therapy of HIV-positive veterans from a large urban Veterans Affairs Medical Center (VAMC), designated an HIV Clinical Center, is presented. The veterans had access to HAART regimens through a multidisciplinary clinic, without financial impediments. This report represents the first analysis from the VAMC, Miami, Florida, U.S.A., concerning the changes in viral activity and immune parameters following treatment of patients with the HIV-1 PI, indinavir, plus at least two RTIs.

MATERIALS AND METHODS

Patients

The patient population consisted of HIV-1-positive patients seen at the VAMC, in Miami, Florida (n = 485; 97% male; mean age, 46.7 ± 9.7 years). Patients were offered triple drug combination therapy if their CD4 count was <200 cells/μl or if their HIV RNA viral load was >10,000 copies/ml and they had attended two earlier scheduled clinic appointments. By these 1996 criteria, 266 patients were offered triple drug therapy which consisted of indinavir, (800 mg every 8 hours), lamivudine (150 mg every 12 hours), and either zidovudine (200 mg every 8 hours) or stavudine (40 mg every 12 hours). Of the 205 patients who accepted triple drug therapy, 152 (74%) had been treated previously with non-PI antiretroviral therapy. For these patients, indinavir was added to their existing antiretroviral regimen. Before starting therapy, baseline assessments were conducted that included complete blood count (CBC), T-cell subset quantitation, and viral load. After starting therapy, patients were observed on a follow-up basis for ∼1 year. During this period, all patients were counseled by a clinical doctor of pharmacy during each of their clinic visits to promote therapy adherence. Based on pharmacy records, the patient population was divided into four treatment groups as follows:

Adherent group consisted of 79 patients who consistently refilled their prescriptions for >4 consecutive months following initiation of therapy and were assumed to represent the most adherent population.

Nonadherent group consisted of 128 patients who failed to consistently refill their triple combination prescriptions over the first 4 months or who ceased therapy due to adverse drug reactions, intolerance or unknown reasons.

Reverse transcriptase inhibitor therapy (RTI-Tx) group consisted of 150 patients who were previously treated with nucleoside analogues and who continued this therapy without indinavir.

No treatment (No-Tx) group consisted of 126 patients who filled no antiretroviral prescriptions during the study period.

Flow Cytometry

In this study, 100 μl of heparinized whole blood was incubated for 15 minutes at room temperature with optimal concentrations of fluorochrome-conjugated antibodies (CD45-FITC, CD14-RD1, CD8-FITC, CD4-RD1, CD3-ECD, and isotype controls). Following incubation, samples were lysed and fixed with Q-Prep and analyzed on an Epics XL-MCL Flow Cytometer. Instruments and reagents were purchased from Coulter Corporation, Hialeah, Florida, U.S.A. Analyses were performed by collecting 2500 events in the lymphocyte region. All determinations were corrected for purity of the lymphocyte gate ⁽¹³⁾.

Viral Load Assay

Plasma HIV-1 RNA levels were measured with the Quantiplex HIV-1 RNA assay (Chiron Corp., Emeryville, CA, U.S.A.). At the outset of the study, this assay had a lower limit of detection of 10,000 copies/ml that was later reduced in the second generation assay to 500 copies/ml. For some analyses, viral load data were grouped as either <10,000 copies/ml or >10,000 copies/ml.

Statistics

Immune and viral measures were determined at baseline and compared with the average of posttreatment measures repeated over the 3-to 8-month follow-up. Data were analyzed using the Wilcoxon signed rank, Spearman's correlation, Mann-Whitney U-test, McNamar's tests, as well as exact probability and linear regression analyses. Data in text are reported as mean ± 1 standard deviation (SD).

RESULTS

To study the response to therapy, patients were assigned to one of four groups, depending on type of treatment and level of adherence. Because, at the start of this study (June 1996), triple combination therapy (i.e., indinavir + two nucleoside analogues) was offered to patients with the most advanced disease or those with the highest viral loads, the baseline health status of the treatment groups differed (Table 1;Fig. 1). The adherent and nonadherent groups were drawn from the same population and did not differ significantly from one another at baseline. Compared with these two groups, the RTI-Tx group had significantly (p < .05) higher lymphocyte count, CD4 percentage, CD4 count, CD8 count, and CD4:CD8 ratio. Compared with these three groups, the No-Tx group had significantly higher CD4 percentage, CD4 count, CD8 percentage, and CD4:CD8 ratios at baseline. The RTI-Tx and No-Tx groups had similar distributions of viral activity at baseline that were lower than those for the adherent and nonadherent groups. Following therapy, the proportion of adherent patients having the highest levels of viral RNA (>10,000 copies/ml) was reduced from 73% at baseline to 16% at follow-up. Conversely, in the adherent group, the proportion of patients having <10,000 copies/ml of virus increased from 27% at baseline to 84% at follow-up (Fig. 1) In the nonadherent group, the proportion of patients having >10,000 copies/ml of viral RNA at baseline was reduced from 69% to 59% at follow-up. The reduction in viral load of the adherent group was highly significant (p < .0001) whereas that of the nonadherent group was marginally significant (p < .05). Changes in the viral loads of the RTI-Tx and No-Tx groups were not significantly different.

Table 1

Fig. 1

Within the adherent group, patients were stratified according to their baseline CD4 count. At baseline, the average viral load of individuals with CD4 counts <200 cells/μl (138,787 ± 194,657 copies/ml) did not differ significantly from that of those with CD4 counts >200 cells/μl (66,481 ± 90,418 copies/ml). Although on average, both the high and low CD4 count subgroups of the adherent population achieved significant reductions in viral load, at follow-up, those with CD4 levels >200 cells/μl achieved significantly lower levels than those with CD4 levels <200 cells/μl (1207 ± 2996 and 118,952 ± 649,197 copies/ml, respectively;p < .01). In addition, 94% of adherent patients with baseline CD4 counts >200 cells/μl had follow-up viral loads of <10,000 copies/ml compared with 18% of those with CD4 counts <200 cells/μl.

In the Adherent group, there was a significant elevation in the mean lymphocyte count of 403 ± 534 cells/μl (p < .004;n = 69) over the 3-to 8-month follow-up period. There were no significant changes in the mean lymphocyte counts for the nonadherent or RTI-Tx groups but there was a significant decrease of 126 ± 422 lymphocytes (p < .0001;n = 50) in the No-Tx group over the 3-to 8-month follow-up. With respect to CD4 percentage in the adherent group, there was a small but significant increase of 4% ± 4% (p = .006;n = 69), whereas there were no significant changes in any of the other treatment groups. Similarly, there was a significant increase in the number of CD4 cells that averaged 111 ± 103 cells/μl in the adherent group, but no significant changes in the nonadherent, RTI-Tx, and No-Tx groups in the course of the follow-up period. The follow-up CD4 count in the adherent group was linearly correlated to the baseline CD4 count and fit the following equation: follow-up CD4 count = 1.1 × baseline CD4 count + 89, r² = 0.74, p < .001. The slope of this regression line is close to unity and suggests the magnitude of this increase was consistent over the entire complaint population, irrespective of baseline CD4 count. Each patient achieved an average increase of 89 CD4 cells/μl, regardless of whether their pretreatment CD4 count was 10 or 500 CD4 cells/μl. The adherent group also experienced a significant increase in the number of CD8 cells that averaged 225 ± 338 cells/μl (p = .005;n = 68). The nonadherent and RTI-Tx groups showed no significant difference in CD8 counts on follow-up but the No-Tx group experienced a significant elevation that averaged 39 ± 243 CD8 cells/μl (p < .04;n = 25). With respect to the mean CD8 percentage, there were no significant changes in any of the treatment groups studied.

DISCUSSION

This study included a review of 483 HIV-positive patients seen at the VAMC in Miami, Florida. Of these, 266 patients were offered triple combination therapy that included indinavir plus two nucleoside analogues, based on their having either CD4 counts below 200 cells/μl or HIV viral RNA levels >10,000 copies/ml. Following a 4-month observation period, patients were liberally defined as adherent if pharmacy records indicated that the patients consistently refilled their prescriptions on schedule. This method for measuring adherence was chosen as it was considered more objective than other measures available in this retrospective analysis. A review of reports from the 6th Conference on Retrovirology and Opportunistic Infections showed that physician assessments and patient self-reports are not reliable measures and tend to overestimate antiretroviral adherence rates ^(14-18). Pill counting demonstrates lower rates of adherence and the use of electronic counting devices yield lower rates yet ^(15,17). Patterson et al. ⁽¹⁴⁾ used the MEMS electronic tracking device to assess adherence; their data suggested that patients had to take their medications on schedule >90% of the time to achieve viral reductions similar to those of our Adherent population. Although pharmacy records provide an objective measure of drug acquisition, the method assumes that patients who do not pick up their medications cannot be adherent because they do not have outside sources of medication. This assumption is supported by two studies that reported that within their VA facilities, between 98% and 100% of the patients relied on the VA pharmacy as the sole source for their medications ^(19,20). The second and less likely assumption of this method is that those who come to the pharmacy to acquire their medications take their medications consistently as prescribed. Because of this, our definition of adherence likely overestimated the number of patients who consistently received the recommended dosages, yet despite this, only 79 of 266 eligible patients (30%) was categorized as adherent. The finding that such a small proportion of eligible patients were adherent was both dramatic and unexpected, given the unimpeded accessibility to care and pharmaceuticals in the VA setting. A preliminary report ⁽¹⁶⁾ from the 6th Conference on Retrovirology showed that only 22% of their hospital based population achieved perfect adherence, confirming our findings of low adherence rates in hospital clinic settings.

Consistent treatment of HIV-positive patients with triple drug therapy resulted in a significant decrease in the plasma viral RNA level. Although the average baseline viral load of patients with CD4 counts >200 cells/μl did not differ from that of patients with CD4 level <200 cells/μl, patients with higher baseline CD4 counts achieved a reduction of viral load at 5 to 9 months that was significantly greater than that of those with low CD4. Patients with baseline CD4 counts <100 cells/μl were 4.5 times more likely to have follow-up viral loads of >10,000 copies/μl compared with those with CD4 counts >200 cells/μl. Between these two subgroups of adherent patients, there were no statistically significant differences in the duration of antiviral therapy before initiation of PI therapy. The relation of baseline CD4 to viral suppression is likely due to the presence of a more complete lymphocyte clonal repertoire at baseline among patients with higher CD4 values. These findings suggest that therapeutic intervention earlier in the course of HIV infection is more likely to lead to complete viral suppression. Inconsistent treatment with PIs or continued treatment with nucleoside analogues alone resulted in less complete reduction of viral load (Table 2). In this study, the decreased viral loads in the adherent population were accompanied by increases in both CD4⁺ and CD8⁺ lymphocytes. Although CD4 cells increased an average of 111 cells/μl, the ratio of CD4:CD8 changed only slightly, from 0.24 to 0.34 because of parallel increases in CD8 levels. This suggests that patients have achieved some degree of immune reconstitution; however, the relative subset distributions remain altered. When the baseline status of the patient was considered, the ability to produce CD4 cells appeared to be consistent (∼89 cells/μl), irrespective of stage of disease at the start of therapy. In fact, the change in CD4 cells in individuals with baseline CD4 counts <100 cells/μl was not significantly different from those of patients with baseline CD4 counts of 200 to 600 cells/μl. This suggests that patients with advanced disease do not show a greater degree of immunologic exhaustion than relatively healthy patients. However, the functional nature of the T cells produced remains to be discerned and will be the subject of future reports.

Table 2

CONCLUSION

The findings of this report support the efficacy of PI therapy in reducing viral burdens and limiting disease progression. We also document that in the setting of an urban VAMC, adherence was low (30%) and produced a direct impact on the success of treatment as judged by immunologic and virologic parameters. Adherent patients experienced significantly reduced viral burdens and elevated CD4 counts. The likelihood of suppressing viral activity depended on baseline CD4 count but the degree of CD4 reconstitution was not. These findings further support the concepts that intervention early in the course of HIV infection is more likely to result in antiretroviral benefit and that adherence to the regimen is crucial for treatment success.

Although these findings support those of multicenter clinical trials, the data presented here are unique in several important respects. Clinical trials suggest that between 65% and 88% of treated subjects achieved undetectable viral loads in the initial months of therapy ^{(9,11,12,21-23)}. In this study, among all who received triple drug therapy, ∼37% achieved undetectable levels. Here, treatment populations were drawn from the total HIV-1-positive cohort at a single VAMC center and as such were homogenous with respect to treatment and standard of care. Within this group, patients were offered therapy based on viral and immunologic parameters and their attendance at clinic. Because this enrollment procedure differs from the selection process inherent in clinical trials, adherence rates reported here are likely to be more representative of care received at regular clinical facilities.

Implications about adherence to regimens and potential to develop rapid resistance underscore the difficulty in translating clinical trials data to practical clinical use. Short-term benefits certainly have occurred. Yet, in this clinic population, in whom adherence starkly contrasts with that seen in controlled trials, the consequence of the rush to ensure HAART therapy and to implement the consensus guidelines of the U.S. National Institutes of Health ⁽²⁴⁾ is yet to be determined. If the efficacy of clinical trials is accepted as true, in practical terms, the implications are: patients do not take their medication reliably more than half the time, resistance to regimens is likely to occur sooner than clinical trials indicate, short-term gains of taking the medications (even inconsistently) are significant.

Acknowledgments:

We wish to gratefully acknowledge the expert technical assistance of Brenda Mattocks and Peter Bocul, the pharmacy data management of Gary Di Patrizo, and the statistical analyses of Robert Morgan, without whom this work would not have been possible. This project was supported in part by grant NIMH5 PO1-MH49548.