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Efavirenz and Rifafour interaction?
Jan 15, 2006

I was just diagnosed with HIV, CD4 count of 4, and although no TB was found, my doctor suspected I have it. I have completed about 1 week of therapy. I am on 4 tabs of Rifafour/day and Combivir and 600mg of Efavirenz. Should my dosage of Efavirenz be increased b/c of potential Rifafour interaction? I have been trying to find out more info but can't find anything conclusive. I am around 60kg. thank you very much for your help.

Response from Dr. Pierone

Hello and sorry to hear about your recent HIV diagnosis. Rifampicin is the main ingredient in rifafour that interacts with Efavirirz (Sustiva). Drug-drug interaction studies showed about a 20% reduction in Efavirenz blood levels from Rifampin. A reduction of 20% should not lead to a dose adjustment of Efavirenz because the levels are typically a good deal higher than needed to achieve virologic suppression. Best of luck to you!

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