About The Study

To compare the impact of multiple Virtual phenotypes (VP) versus multiple Virtual Phenotypes plus baseline phenotype (VPP) resistance testing in the treatment of heavily pretreated individuals initiating multiple drug rescue therapy (MDRT).

Study Approach

This was a prospective randomized study. Participants who had experienced failure with multiple courses of antiretroviral (ARV) therapy and whose multiple genotypes (interpreted by Virtual Phenotypes) revealed decreased susceptibility to at least two classes of ARV medications were randomized to receive either a MDRT tailored according to their existing Virtual Phenotypes only, or a MDRT further tailored according to a baseline phenotype (performed at study entry). The first group would receive up to 10 antiretroviral drugs, selected according to history of drug exposure, tolerability and lab test results (including up to four nucleoside reverse transcriptase inhibitors; up to three protease inhibitors; one or two non-nucleoside reverse transcriptase inhibitors; plus the drug hydroxyurea for the purpose of enhancing the activity of the nucleosides. The second group would receive a regimen of at least four drugs tailored by excluding the drugs to which the virus was shown to be resistant on the phenotype at baseline. All participants interrupted treatment for at least one month before starting their new ARV regimen.


Initial target population was 60. At the end of the trial, 28 participants with extensive ARV experience and in whom these drug regimens had failed, had been enrolled. The median age was 37 years.


The study was terminated with 28 patients enrolled. New drugs became available after the beginning of the study and these drugs tended to be used for all participants in both study groups. Ultimately, the predominant and most powerful drugs in both groups were identical.

Participants received a median of five and six drugs in the VP and VPP groups, respectively. All patients received a boosted PI. Three VP and four VPP participants took an NNRTI. The overall proportion of participants who ever achieved viral load below 50c/mL was 50% and was the same in both groups. Median time to reach this viral load was 12 weeks for both groups. CD4 counts, viral loads and the proportions of participants with viral load below 50c/mL at weeks 12, 16 and 20 were the same in both groups, as were negative drug reactions and drug discontinuation.


In a setting where multiple Virtual Phenotypes are available, additional information obtained from baseline phenotypic testing (to determine what drugs each participant’s virus was still vulnerable to) did not substantially affect the complexity, tolerability or efficacy of MDRT regimens. The widespread use of boosted PI regimens in this study probably affected this outcome

Note: This summary summary was taken from the 1st International Aids Society Conference on HIV Pathogenesis and Treatment, 2001.