A failure to respond to HAART with a 2 log drop in viral load within four weeks doesn't necessarily indicate total treatment failure, according to a study of 335 individuals starting HAART at the Frankfurt UNI Clinic. Viral load after eight weeks on treatment is probably a better guide.
An analysis by Alessandro Cozzi-Lepri of Royal Free and University College Medical School, London, showed that only 40% of those who started treatment hit the level (a 2 log decline in VL after four weeks) defined as the expected treatment response by US treatment guidelines.
"The way I interpret this guideline is that patients whose viral load does not drop by 2 log by week 4 would be possible non-responders" said Alessandro Cozzi-Lepri, "yet there are not many data to support this recommendation".
Even data supporting the opportunity to detect potential failure at week 8 are limited.
John Mellors told the Seventh Conference on Retroviruses last month that it was very difficult to predict long-term response when looking at viral load measured eight weeks after starting treatment. Only 10-20% of patients could be identified as "off-track" after eight weeks, and that poor performance at week 8 was not predictive of the subsequent viral response (Huang).
In the Frankfurt UNI Clinic cohort viral load was still detectable in the majority of patients at week 4.
However by week 8, 70% of patients were responders, and by week 16 80% were responders.
The value of checking viral load at week 4 may be greatest in patients who start treatment with very high viral load (above 1 million copies). Only three out of 12 individuals who started with high baseline viral load went on to achieve undetectable viral load (below 500 copies) if they did not experience the 2 log viral load decline within four weeks.
In contrast, 11 out of 14 people with viral load between 100,000 copies and 1 million copies achieved undetectable viral load at week 16 despite failing to experience a 2 log drop in viral load within four weeks of starting treatment.
The Frankfurt study suggests that week 8 viral load is a more reliable guide to subsequent response.
In those with viral load below 10,000 copies but still detectable at week 8, however, the chances of achieving undetectable viral load by week 16 seem to diminish. Only 38% of those who remained above 10,000 copies at this point went on to reach undetectable viral load.
Reference
Cozzi-Lepri A et al. The viral response to HAART over the first 16 weeks of therapy according to the pre-HAART and the 4-8 week viral load. Sixth Annual Conference of the British HIV Association (BHIVA), abstract O19, 2000.