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Meds and Timing
Jun 30, 2004

I am taking Sustiva, Epivir and Viread. I also take Pentasa for Crohn's disease. I'm doing very well. My question is what is the maximum time variance allowable? If you usually take it at 6:00 AM what would be the latest that you could take the combo on the weekend? I've heard three hours is the max. What's the truth? Thanks, Mike

Response from Dr. Sherer

This is an important question for the entire regimen, and its useful to understand that the answer varies with each drug.

Sustiva has the longest half-life, up to 40 hours. Tenofovir also has a long half life that allows for once daily dosing, e.g. 26 hours. Epivir has a shorter half life, 4-6 hours, in the plasma, but has been shown to be effective when used twice daily, and more recently once daily, due to the accumulation of active drug in the intracellular compartment.

So the principal concerns with delays in the am dose in a once-daily regimen are the lamivudine (Epivir), and to a lesser extent the tenofovir (Viread) and the efavirenz (Sustiva).

Both efavirenz and lamivudine are genetically vulnerable, i.e. a single mutation leads to resistance, and with both drugs this can occur very quickly, i.e. within hours or days of an inadequate blood level of drug.

So with that knowledge of the risk, and the absence of reliable data on this regimen used once daily, I am not willing to give a number of hours within which it is 'safe' to take the drug. Any delay is a bad idea, and I would discourage planning for it. I would reframe the question: How can you gradually change the usual time of day that you take your medications to allow for sleeping late on weekends?

I urge you to talk to your doctor about this question.


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