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HIV Drug ResistanceHIV Drug Resistance
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Stop antivirals while await resistance test results
Apr 29, 2001

I could swear I read somewhere that all antivirals should be stopped while awaiting resistance test results. Your thoughts? Thank you.

Response from Dr. Little

Unfortunately, I do not have a universally agreed upon answer. In general, ongoing viral replication in the setting of drug resistance may permit further (ie more) selection of drug resistance mutations. That is, in general, the longer you stay on therapy that is failing, the more likely you are to acquire more drug resistance over time to this drug. Now for some drugs, you only need one resistance mutation to cause high level drug resistance (ie nevirapine, efavirenz, 3TC). For these drugs, it seems possible that once you have drug resistance, the damage is done and ongoing therapy with the drug is unlikely to make things worse (at least with regard to these drugs). On the other hand, for drugs which require (in general) multiple mutations or changes to occur in order for the drug to fail, the continued use of these drugs in the setting of treatment failure (ie, a detectable viral load) has the potential of making things worse over time. I think that most physicians in the field would probably agree, that it is desirable to change therapy in the setting of drug resistance sooner rather than later, that is, while the viral load is still relatively low (perhaps less than 10,000 copies/ml), but this is more opinion than data. In general, if you can get drug resistance test results back in 2-3 weeks, there is probably not a great deal of harm in continuing therapy during this period. However, if one of the drugs in the regimen is nevirapine, efavirenz, or 3TC, I would probably be at least tempted to stop all therapy while awaiting test results - not because I am worried about resistance to one of these drugs getting worse, but because if the cause of the increase in viral load is because of failure of a different drug in the regimen, then the 2-3 weeks you wait for drug resistance test results might be sufficient to develop drug resistance to one of these three drugs. Overall, though, most providers I expect will continue therapy while awaiting test results unless there are cirucmstances such as these (or perhaps other concerns about toxicity) which would suggest that it would be safer to stop temporarily.

The Roche T20 Trial
differences between pheno and geno testing

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