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When to do genotype and Viral load tests
Jan 20, 2002

After starting a new drug regemine is there any guideline for how soon after should a viral load test be done? Secondly, how much of a decrease should one expect on the drugs in a given period of time to be sure they are working?

Response from Dr. Little

This should be - but is not - a simple question. In a person who has never taken any therapy who is started on treatment, most physicians would test after 3 months. The rationale to test earlier, is in cases where there are concerns about drug resistance or treatment compliance, or potency. But in general, every three months is considered fairly standard. Once on therapy, every three months is also fairly standard, but again, there are many circumstances where more frequent monitoring may be warrented.

In terms of how much of a decrease should one see - again, this depends on the starting viral load. In general, one would like to see the patient reach an undetectable viral load by week 16-24 of therapy (it will take longer for someone with a high starting viral load). This generally means that you will see more than a log HIV RNA drop in the first 4-8 weeks. Again, the drop may be slower in someone with drug resistant virus - which is why as proposed above, we may check sooner than 12 weeks to determine if we think things are going too slowly and want to intensify or change therapy. The failure to reach complete viral suppression (ie viral load less than 50) by week 20 or 24 is a sign of impending failure in most cases. Also, the failure to see a drop of at least a log HIV RNA by week 4-8 is also a warning of impending failure in many cases.

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