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Nov 6, 2000

I am taking Combivir and Viracept - what is considered a missed dose? and if I miss one dose is that bad?

Response from Dr. Cohen

Well -- first. It is easier to talk about this not so much as bad or good, but what might happen if... since the issue with a missed dose is whether that given enough of a chance for HIV to restart growing and then maybe "learn" how to become resistant to the very meds that were working.

In general, the answer is no, one missed dose ain't enough. As for what is a missed dose, we usually mean that it is a dose you missed. Meaning you didn't take it. There is some flexibility in time usually -- so if you took it but it was a few hours late, that may still be OK. That would be a near missed dose. If however you missed a dose, you should not just take twice as much the next time. This doesn't help and may just add side effects.

It also might matter what the viral load was when you missed the dose. Since, if the viral load was "undetectable" meaning below 50 copies, it appears on average to take over a week when someone completely stops the meds for HIV to grow back above 50 copies. And when HIV is controlled to this degree (<50), a rare missed dose probably doesn't cause trouble. On the other hand, if the viral load is detectable and more HIV is growing, this might give it more of a chance. This is mainly an issue when starting a cocktail and establishing suppression for the first time -- since when just starting with a detectable viral load, HIV will be sensitive to the meds, and an occasional missed dose might allow a lower blood level of the med while it is still growing -- this lower blood level would not be enough to stop it from growing, but enough to encourage it to mutate in a way that helps it learn to ignore that med.

We have seen in studies that perhaps 5% of those who missed even one dose in a week will lose some of the potent effects of the combo -- so it can happen on some of these combos -- but is not likely.

Good luck.


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

Viral Blips
Starting Sustiva again

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