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Genotype and Phenotype Results
Sep 6, 2002

Hello doctor:

I was on Viracept, AZT and Epivir for over 2.5 years and have been HIV+ for about the same.. My viral load went up for several visits so I took the above listed tests. My first question is, why does the genotype list Viracept as a drug I have "NO" reistance to, yet the bar graph of the phenotype is to the right where it indicates it as a non effective agent? Also, I show resistence to Sustiva, Rescriptor and Viramune, yet I never have taken an NNRTI.. How is this possible? I show that I am still VERY responsive to Retrovir, Bascially, what I ended up doing was change my epivir (which had a bar to the right off the page clearly showing major resistance) to Viread (Tenofovir) and am contuning to use Viracept and Retrovir. Because Viracept is one of those protease inhibitors with the unusal characteristic of not having much cross resistance to other PI's and the fact that I can not use Sustiva or any other NNRTI in the future, I decided just to change my NRTI, Epivir, to Viread... Hopefully now my VL will go back down. I mean, if the genotype says I have no resistance and the phenotype says I do then what do I go by? My doc feels comfortable with my choice. Please advise!!! Jason From NYC

Response from Dr. Little

First - regarding what appears to be a conflict between the genotype and phenotype test. If the bar graph of the phenotype test shows that you are not sensitive to viracept and yet the Genotype shows no resitance to viracept, I would guess that the reason your phenotype test is showing resistance is on the basis of other protease inhibitor resistance mutations. With the protease inhibitors, there is some degree of partial resistance that comes with multiple resistance mutations to protease inhibitors, some times despite the fact that the one PI in question does not have the typical mutation for that drug that is associated with drug resistance.

Regarding the apparent resistance to the NNRTI class, if you have been infected for about 2.5 years and have never taken this class of drugs, then it would appear that the person who transmitted HIV to you passed a drug resistant virus. This is called transmitted drug resistance and is on the rise in North America.

Overall, if your phenotype shows that you have resistance to viracept, I would be reluctant to continue this drug as your protease inhibitor. The PI Lopinavir/ritonavir (known as Kaletra) is one that I typically recommend in patients who have some degree of PI resistance. Based upon your description of your complex phenotype and genotype results, I think that someone who is very familiar with HIV drug resistance should review the test results and discuss your therapy with you to help you make the best possible decision.


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