The study included 221 eligible participants drawn from the REACH (Research on Access to Care in the Homeless) cohort of HIV positive homeless and marginally housed individuals in San Francisco.
A majority of patients were men, the median age was 44 years, and the median CD4 T-cell nadir (lowest-ever level) was 206 cells/mm3. Most were taking non-nucleoside reverse-transcriptase inhibitor (NNRTI)-based (37%), ritonavir-boosted protease inhibitor (PI)-based (28%), or unboosted PI-based (25%) combination regimens.
The investigators determined adherence to ART through pill counts conducted during unannounced visits to each participant's place of residence. Viral suppression was defined as maintaining a viral load < 50 copies/mL, while virological failure was defined HIV RNA > 50 copies/mL.
Results
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Comparing the probability of virological failure just after achieving viral suppression versus after 12 consecutive months of suppression, there was a statistically significant decrease in the probability of failure with longer suppression, as long as adherence was greater than 50%. |
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The estimated difference in risk, comparing the probability of virological failure after 1 month versus after 12 months of continuous viral suppression, was as follows: |
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0.47 less among patients with 50%-74% adherence; |
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0.29 less among patients with 75%-89% adherence; |
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0.36 less among patients with 90%-100% adherence. |
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"The risk of virologic failure for adherence greater than 50% declines with longer duration of continuous suppression," the study authors concluded. "While high adherence is required to maximize the probability of durable viral suppression, the range of adherence capable of sustaining viral suppression is wider after prolonged periods of viral suppression."
In their discussion, the researcher noted that these findings are supported by several recent induction-maintenance ART studies. It has been shown, they wrote, that lopinavir/ritonavir (Kaletra) monotherapy "leads to higher rates of viral suppression once patients achieve suppression on standard regimens" than when monotherapy is used initially.
In addition, they continued, use of a triple nucleoside/nucleotide reverse transcriptase inhibitor (NRTI) regimen "appears to be more effective after viral suppression is achieved than when the regimen is used as initial therapy."
Finally, the authors wrote, "While the adherence proportion required to sustain viral suppression may decline over time, the goal of near perfect adherence should remain unchanged."
In addition, they stated that while both more potent therapy and sustained viral suppression may lessen the virological consequences of missed drug doses, "improving adherence will increase the probability of durable and sustained viral suppression."
Department of Medicine, University of California at San Francisco, San Francisco, CA; Division of Biostatistics, School of Public Health, University of California at Berkeley, Berkeley, CA; Massachusetts General Hospital Center for Global Health, Harvard Medical School, Harvard Initiative for Global Health, Boston, MA.
10/06/09
Reference
M Rosenblum, SG Deeks, M van der Laan, and DR Bangsberg. The risk of virologic failure decreases with duration of HIV suppression, at greater than 50% adherence to antiretroviral therapy. PLoS One. September 29, 2009. (Abstract).
