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5-on and 2-off
Jun 13, 2002

Dr. Cohen,

A friend of mine was told by his doctor that he could try a 5-day on and 2-day off regimen. My viral control and cd4 count is similar to his (undetectable and > 350), and this is something I am interested in learning more about. However, what is the risk of viral resistance developing?

Response from Dr. Cohen

Good question. Not sure where you are located, but this is actually the focus of research that our group is just starting - to answer your question and to see how well that approach would work.

We have learned in the past year that for those with a viral load below 50 copies for some time for some regimens, there can be some flexibility in terms of dosing. Meaning that in a very small study of ten people whose viral loads were suppressed for years to <50 copies on a combo of zerit, epivir, and crixivan with low dose norvir, they were able to maintain control of their HIV even if they took their regimen just for 7 days on, followed by 7 days off, followed by 7 on, etc. After about a year, the group of ten have maintained control. With, as far as we've heard, no resistance developing. Now, there are some "blips" of viral growth in the 7 day off period, but they resuppress after a week on.

But that is the only strategy of "brief" interruptions that has been studied with successful results presented. While other schedules may work, we don't know yet. And other studies of brief interruptions were stopped early when they were not working. For example, there was a short study using the reverse of what you ask about - five OFF, two ON - and that was stopped quickly after there was a loss of suppression in the first 3 people. So other work is now underway to evaluate other ratios of offs and ons. And whether this is limited to those who are on a PI based regimen, versus one with other meds such as nonnucleosides.

As I mentioned, our group in Boston is just near to launching two studies exploring this schedule you ask about - (assuming the FDA allows us to proceed). But the studies have not been done to answer your question. So I cannot say what the risk of resistance is - yet. But we hope to answer it in these next months. And we are certainly interested in those who live near to Boston or Springfield Massachusetts getting in touch with us to join these small studies to help us quickly answer these questions. We plan to explore this issue for those on both PI and nonPI based combos. To see if these studies are an option for you - click here to get to our web site to see where we are and how to contact us.

So - your friend's doctor may have an informed guess or even a prediction of the answer - but some pauses in regimens have worked out, while others have not. And when the research by our group, and perhaps others is done, we should be better able to answer this question about flexibility...

Tenofovir & Didanosine Dosing
in the pipeline...

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