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What is the deal with the VIRCO Assay(s)
Jul 21, 1998

I read that a group in Belgium, VIRCO, is developing something called the RT-antivirogram which provides phenotypic resistance testing of the nucleoside

analogue drugs and the non-nucleoside reverse transcriptase inhibitors. Is it only for nukes and NNRTIs? What about PIs? Is this test available to the general public at all? And do you think it is a really helpful test? Have there been any clinical trials or the like to validate the effectiveness of the test(s)? Thank you for your work here.

Response from Dr. Holodniy

The VIRCO antivirogram is an assay which takes the reverse transcriptase and protease enzymes from a patient's strain of HIV, and inserts them into the backbone of lab adapted strain of HIV. Initially used to look at the RT inhibitors, the assay has been expanded to also look at PIs as well. The advantage of this assay is it simulates the antiviral response a specific patient strain might have to various drugs. Some people believe that measuring the growth of the patients virus is a better indicator of future response than genotyping the virus. This constructed virus is grown in the presence of each drug individually. Thus it suffers from not being able to put 3 or 4 drugs into culture simultaneously (too toxic to cells necessary to grow the virus)that would better simulate what we would be giving patients. The assay is becoming more widely available in the US, with plans to set up labs here. The cost is several hundred dollars and results may take a few weeks to get. It has been used alot in survey studies to assess the amount of drug resistance in various communities, and as a test tube aid in predicting responses to newer agents. Although alot of anecdotal info from treating docs is out there (differing opinions on it's utility), no prospective studies have been completed which demonstrate a virologic or clinical advantage to the patient after using the information.

MH



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