Switching to Sustiva
Aug 8, 2003
Dear Dr. Boyle, I have been on Trizivir plus Viramune now for 4 months and my VL has not yet gone to undetectible - it hovers between 200 and 400. Before completely switching my cocktail, my doctor suggested switching from Viramune to Sustiva and see if that makes a difference. Do you think it will? Also, if I'm not able to tolerate Sustiva and need to return to Viramune, will I have to do the half pill dose for 2 weeks again before going to full dose Viramune? I worry about that will allow the virus time to become even more resistant to Viramune. Thank you for your time.
Response from Dr. Boyle
Since you've been on Trizivir and Viramune for only 4 months it may be too early to tell if you are going to eventually get to <50. Some patients, especially those who start with high viral loads, may take 6 months or longer to get to <50. So, I would consider giving it a little more time. As far as your other questions, unfortunately, we don't have definite answers. Since Sustiva (efavirenz) appears to be a more potent antiretroviral than Viramune (nevirapine), it is possible that you may get some additional viral suppression with it. As far as the dosage adjustment of Viramune when switching from Sustiva to Viramune, there is very little information. Since Viramune is metabolized by the Cytochrome P450 isozymes, and predominantly the CYP3A family, and Sustiva induces these enzymes, one would think that if you have been on Sustiva for some time that the correct starting dose for Viramune would be 400mg (i.e., no lead in dosing); however, I am unaware of any data that establishes the safety of this approach. Of course, there are risks of either approach: If you don't use the lead in dose (i.e., 200mg daily for the first 2 weeks then 400mg daily) you may be at higher risk for hepatotoxicity and rash and if you do use the lead in dose, you may be at higher risk of virologic failure. While I cannot make a recommendation, since I don't ahve the data to do so, my clinical practice is to use the lead in dose if the patient has been on Sustiva for <1 month, and to start with 400mg if the patient has been on Sustiva for >1 month. Fortunately, almost all of my patients tolerate Sustiva well, and almost all of those who don't stop it within the first two weeks, so I rarely have to make this difficult decision. Finally, if you make the switch and don't tolerate Sustiva an alternative approach is to avoid the issue and switch to a protease inhibitor, and now with Reyataz (atazanavir) available you have a once-daily protease inhibitor to choose from.
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