July 27, 2005
Last summer, at the XV International AIDS Conference, we were presented with the results of the courageous lopinavir/ritonavir (LPV/r, Kaletra)-monotherapy study.1 In that study, led by Joseph Gathe, a group of 42 HIV-infected patients with long-term virologic suppression were randomized to continue on their current regimen or to simplify it to lopinavir/ritonavir monotherapy. Over 48 weeks, virologic suppression was maintained in 95% of the control group as compared to 81% of those on monotherapy. In this latter group, 4 patients had detectable viremia; this included 1 person lost to follow-up and 3 true virologic breakthroughs.
There was some concern that it was only a matter of time before the other patients receiving monotherapy experienced the same fate: They may still have "undetectable" plasma viral loads, skeptics said, but those viral loads must be rising under the measurable threshold, and would surely break through soon.
To assess this possibility, J.E. McKinnon, from the University of Pittsburgh, and colleagues in Madrid, Spain, used an experimental Roche Amplicor PCR assay with a limit of quantitation of 3 copies/mL, and applied it to samples collected at weeks 4, 8, 12, 24 and 48 in both of the lopinavir/ritonavir-monotherapy study groups.
In patients with undetectable viral loads, the researchers were able to demonstrate a stable, low-level viremia of 3 to 5 copies/mL in more than 70% of the samples, with no trend towards an increase in any of the samples in either group. In the 3 patients who did have a virologic breakthrough in the lopinavir/ritonavir-monotherapy study, each breakthrough was preceded by a slow, steady increase in viral load beginning at week 8 and eventually exceeding 50 copies/mL by week 32.
This study clearly demonstrates that full virologic suppression can be maintained with a single agent in selected patients who have previously experienced long-term suppression while on HAART. This means that it is ethical, and even important, to pursue clinical trials on this approach. Doing so may allow us to better define the type of patient for whom single-agent therapy might be most appropriate, as well as which specific agents can be used. (For instance, trials of atazanavir [ATV, Reyataz] + ritonavir [RTV, Norvir] are ongoing.) Until the results of these studies are available, however, the single-agent approach will remain an experimental one -- and one that should not (at least, not yet) be offered to our patients as a standard of care. Perhaps next year.
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