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Experts Differ In Interpretation of Resistance Testing Results
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"Experts select different antiretroviral drug regimens whenpresented with resistance data in the form of genotype, phenotype, or combined genotype plus phenotype"
XIII International HIV Drug resistance Workshop
Canary Islands, Spain 8--12 June 2004
I am emailing selected program book abstracts from conference to you in addition to my reports to be followed by summary reports and interpretation by researchers attending conference and writing for NATAP.
ABSTRACT 116
Antiviral Therapy 2004; 9:S130.
AR Zolopa1, M Bates2 and N Parkin2
1 Stanford University, Stanford, Calif., USA; and 2 ViroLogic, Inc.,
South San Francisco, Calif., USA
Note from Jules Levin; this study shows that the leading world resistance experts can look at the same resistance tests reports and have different interpretations. Like other similar studies previously reported these study results show how difficult it is to interpret test results and make appropriate treatment recommendations to patients. Oftentimes, a medical provider will use and rely on the interpretation of test results provided by the lab testing the patient blood sample. This interpretation should be subject to perhaps more scrutiny. The best advice to provide in interpreting test results is to realize the limitations of the data provided and to realize your own limitations in interpreting the information and in making treatment choices. Using a patient's treatment history in combination with good intuition based on knowledge of HIV drug resistance are important tools. Caution is advised to patients and care providers.
BACKGROUND: The clinical utility of combined phenotype (PT) and genotype (GT) resistance test results (PTGT) compared to PT or GT alone for theselection of antiretroviral (ARV) regimens in treatment experienced patients has not been demonstrated. We sought to determine if the provision of PTGT test results changed ARV choices by an expert advisory panel, compared to having the same GT or PT but given separately.
METHODS: Thirteen experts attending a closed advisory meeting recommended ARV regimens for five patients based only on actual GT (GeneSeqHIV), PT (PhenoSenseHIV) or PTGT (PhenoSenseGT) results.No other clinical information was provided. All samples had at least one drug with GT/PT discordance. Causes of the discordance included the presence of mixtures, suppressive effects, and cross-resistance not accounted for by the genotype.
RESULTS: In a three-way comparison of ARV choices based on GT, PT or PTGT, differences were seen for all 15 ARVs selected by at least one expert (delavirdine and zalcitabine were not selected by any). The degreeof difference for each drug (percentage of differences compared to maximum possible differences based on frequency of selection) ranged from 100% for nevirapine and atazanavir to 13% for lamivudine. The mediandifference was 47% -- that is, nearly half the time a drug was chosen based on one test result it was not chosen based on at least one of the other tests. The number of differences was larger for GT vs PT and GT vs PTGT compared to PT vs PTGT, especially for tenofovir and to a lesser extent for abacavir, amprenavir, indinavir and saquinavir. GT tended to result in less abacavir, didanosine and efavirenz selection compared to PT or PTGT, and more tenofovir and saquinavir selection. Lamivudine and lopinavir/ritonavir tendedto be used more frequently based on PTGT compared to PT alone.
CONCLUSION: Expert clinicians/virologists make different regimen choices based on GT, PT, or PTGT. Since provision of PTGT results can lead to different ARV choice there is potential clinical value to having the combined results, at least in certain settings. We cannot determine if these differences in ARV choice lead to differences in clinical outcomes.
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