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Predicting Response to DDI
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"Prediction of Early HIV-1 RNA Reduction in the Jaguar Study Using Phenotypic Susceptibility to DDI"
12th CROI Feb 2005
Reported for NATAP by David Margolis, MD
Univ of Texas, Southwestern Medical Center Dallas; VA Dallas; ACTG
The likelihood of response to ddI has been notoriously hard to assess with genotypic or phenotypic assays. Michael Bates of ViroLogic (abstr. 105) made a valiant attempt to provide data to aid those using the Phenosense phenotype in assessing the potency of ddI. Patients experiencing a virologic failure on combination therapy were randomised in the Jaguar study to receive ddI (n = 110) or ddI-placebo (n = 58). They assessed 2 virologic outcomes: the magnitude of reduction in HIV-1 RNA by week 4, or the protocol-defined virologic response of ≥ 0.5 log10 viral load reduction or week 4 viral load < 50 copies/mL. 98 patients in the ddI arm were available for analysis. had both fold change in ddI and week-4 virologic response available. The median decrease in HIV-1 RNA was 0.57 (Inter Quartile Range, 0.15 to 1.02) and the median fold change in ddI was 1.65 (IQR 1.46 to 1.97).
Patients with a fold change to ddI £ 1.3 were very likely to respond to ddI (15 of 18; 83% responders). Conversely, patients with a fold change to ddI ≥ 2.2 were unlikely to respond to ddI (4 of 14; 29%). However, the bulk of the patients studied had an intermediate fold change (1.3 < fold change < 2.2) and a 50% chance of responding (33 responders of 66). Bates presented reassuring data showing that the FC assay was reproducible within a very tight range, given the narrow range of FC's reported. These findings are a step forward, albeit an incomplete one. If the data is widely applicable, about one-third of patients will have FCs that predict ddI success ( 1.3) or failure ( ≥ 2.2), and two-thirds will have FCs that are as useful as a coin flip. But some information is better than none.
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