Selection of Antiretroviral Therapy Guided by Genotypic or Phenotypic Resistance Testing
 
The phenotype/genotype (PhenGen) open-label, randomized, multicenter study evaluated the genotype/virtual phenotype (vPt) and real phenotype (rPt) for choosing a new HAART regimen at failure.

Patients with a plasma viral load (pVL) between 2000 and 200,000 copies/mL and a CD4 cell count >200/muL, failing >/=2 regimens (<6 drugs), were randomized for vPt or rPt.

Three hundred three patients were enrolled: 111 and 108 patients received a new treatment in the vPt and rPt arms, respectively. The 2 groups were comparable for baseline patient characteristics and treatment history.

Results

The new therapy was in agreement with expert advice in 58.5% of cases.

After 6 months, no statistical differences were found in the mean absolute change from baseline CD4 cells (+55 and +46 cells/microliter; P = 0.7), mean pVL log decrease (-1.35 and -1.37; P = 0.8), or proportion of patients with a pVL <400 copies/mL (54.8% in vPt arm and 52.6% in rPt arm; P = 0.9).

At multivariate analysis, variables independently associated with failure of the new regimen were: pVL at baseline, number of nucleoside reverse transcriptase inhibitor-associated mutations, number of protease mutations, and recycling of indinavir.

Patients' adherence to the prescribed regimen, number of active drugs in the new regimen, and adherence to expert advice predicted virologic response.

The authors conclude, “The virtual genotype is as predictive of treatment outcome as the real phenotype.”

“Use of expert advice significantly improved the response to therapy.”

12/10/04

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