|Understanding PhenoSense comprehensive profiles
Jul 19, 2001
I have been diagnosed with AIDS since 1994. I have been on all the current drugs in combinations with failure to increase my CD4 count or maintain a low viral load. I have had two Genotype test done over a two year period, each showing mutation and resistance. My doctor wanted to see the results of a PhenoSense test. He circleed the last column which showed blackened bars for every drug each reaching in varying degrees to maximum drug resistance. He told me I am resistant to all but some bars are not as long as others. Does this mean some are a little less resistant? He would like to get me on the expanded access for tenofovir the new nuclueotide but I am hesitant about added one more drug due to my track record. I would prefer to take my chances and wait for another drug with it,like T=20. I know his concerns have been recent bouts with pneumonia and KS.I did stop my Zerit without telling him because I figure It is resistant and has cause such lipatropy, and increase pain with my peripheral nueropathy despite 1200 daily of neurontin and darvocet. I seem to feel less tire. How acturate are these phenotype and genotype testing in directing care? Where do I go from here. I now am a firm believer in starting HAART drug later than sooner. I know sometimes there isn't a choice when initial T=cell counts are in single or double digits. I am sorry for such a long written inquiry but I am curious over the clinical information these test offer to the physcian in dictating care. Thank you for your time Tom
Response from Dr. Little
Dear Tom, You are correct that the presence of dark bars to the right of the desired range on a PhenoSense test do indicate drug resistance. To a degree, lower bars may mean less drug resistance, but this is not universally true. That is, for drugs like d4T (stavudine) and ddI (didanosine), we rarely see high level drug resistance on these test - DESPITE the fact that someone may have complete drug resistance as demonstrated by failing this drug when used in an otherwise ineffective treatment regimen. When faced with drug resistance by phenotype and genotype testing, I generally look to the CD4 count for guidence. If the CD4 count is high enough (ideally greater than 200), then you have a bit more room to wait for something better to come along (for instance, something to combine with T20). However, if the CD4 count is quite low (for instance less than 50), then you may benefit in the short term from some therapy, even if it is not sufficient to make the viral load undetectable or to make the CD4 count rise substantially. CD4 counts between 50 and 200 represent a kind of grey zone - for me, this means that I look to what trials (generally the best access to investigational drugs in combination, rather than expanded access, which is more likely to offer one new drug to combine with several of your older drugs) are available in your area and which ones you might qualify for. I understand your physician's concern about waiting at all if you are having trouble with pneumonia and KS. In general, if you are at risk of developing HIV-associated diseases (such as opportunistic infections or cancers), because of advanced immunosuppression, then I would talk to your doctor about making up the best available regimen (in a clinical trial or the best the two of you can come up with together) and start. As far as which drugs to pick based upon the PhenoSense test, you can discuss this with your doctor based upon your test results. If you want more information on the PhenoSense test and how the results are interpreted, why don't you look up the web site: www.virologic.com - there is a great deal of information on this site. Good luck.
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