The need for perfect or near-perfect adherence to HIV treatment is less important after a patient has had an undetectable viral load for at least a year, US research published in PLoS One suggests.
The research, in 221 patients, suggests that – after one year with an undetectable viral load – a patient may miss up to half of his or her doses and have no more than a 2% probability of viral rebound, compared to a 49% probability of viral rebound at this adherence level after just one month with undetectable viral load.
Adherence is the single most important factor under a patient’s control to the success of his or her antiretroviral therapy. Near-perfect adherence was necessary for sustained HIV suppression with older HIV drugs, and even newer antiretroviral agents require very high levels of adherence.
However, new research suggests that higher levels of adherence are needed to suppress HIV in the initial period after antiretroviral therapy is started than are required once viral load has been undetectable for a sustained period.
A team of investigators led by Dr David Bangsberg of the Harvard Initiative for Global Health, with researchers from the University of California, San Francisco, hypothesised that the impact of adherence on the risk of viral load becoming detectable would differ according to how long a patient had previously maintained an undetectable viral load.
They therefore undertook a study involving 221 patients to determine the effect of adherence on viral load after differing periods of HIV suppression.
The study ran between 1998 and 2007. Adherence was measured by an unannounced pill count at the patient’s home every three to six months, and each individual was enrolled in the study for twelve months.
The level of adherence ranged from 0 to 100%, with a median of 92%.
All 221 patients in the study initially achieved virological suppression, but 108 (49%) experienced a subsequent rebound in their viral load.
Statistical analysis showed that a lower risk of virologic failure was associated with a longer duration of viral load being suppressed to undetectable levels, and taking a non-nucleoside reverse transcriptase inhibitor (NNRTI)-based combination of drugs.
For all levels of adherence of 50% or above, there was a significant fall in the risk of viral load rebounding after twelve months of HIV suppression compared to after one month of viral load being undetectable.
An adherence level of between 50 and 74% after a month of successful HIV suppression was associated with a 50% risk in viral load becoming detectable. However, after a patient had maintained an undetectable viral load for a year, adherence of this level was associated with a risk of approximately 2% of HIV rebounding to detectable levels.
Nevertheless, the investigators caution that “while the adherence proportion required to sustain viral suppression may decline over time, the goal of near-perfect adherence should remain unchanged.”
They conclude, “While both more potent therapy and sustained viral suppression may lessen the virologic consequences of missed doses, improving adherence will increase the probability of durable and sustained viral suppression.”
Rosenblum M et al. The risk of virologic failure decreases with duration of HIV suppression, at greater than 50% adherence to antiretroviral therapy. PLoS One: 4 (9).