Could it be some resistance between abacavir and sustiva?

Thank you for your answer.

Well... not clear what exactly you mean. But let me take a guess...

These meds are from two different classes of antivirals. Abac is a nucleoside, and sustiva is a non-nucleoside. As a result of being in two different classes, when/if HIV has a chance to develop resistance to one of these drugs, it would not also create cross resistance to the other drug. Say, if you were on an abacavir containing combo, but not on sustiva nor on any other non-nucleoside (viramune and rescriptor are the others) -- and if HIV was growing while you were on abacavir -- you will likely start developing resistance to the abacavir, but you would NOT expect that resistance to give you resistance to the Sustiva. Since it is a different type of antiviral. And there is no cross resistance. And the same is true in reverse...

Now just to clarify further. If you are on any nucleosides other than abacavir and HIV starts growing -- this resistance can over time "teach" HIV how to ignore other meds you haven't used yet -- including abacavir. That is because abacavir is a cousin of the other nucleosides, and HIV takes the tricks it uses to ignore some of them to learn how to ignore all of them. That is why we tend to want to do something to the combo when we start to see resistance -- to avoid the risk of losing other meds as well.

Hope that clarifies.

Cal Cohen, M.D., M.S.