Dear Dr.,

I'm about to start treatment with Atripla. I just found out on one of the forums that the Sustiva portion of it might interact with Propecia which I've been taking for years now for managing hair loss (both meds utilize the same enzyme - 3A4). My Dr didn't mention anything to me about that so I doubt he's aware of it (there's no warning on either med's leaflet). My question is: do you think that that interaction is substantial? Should I be halting my Propecia intake or just be monitoring it, and if so - what should I be monitoring for??

Thank you very much!

Thanks for your question.

It is true that both medications are metabolized by the liver using the same enzyme (P450 CYP3A).

Sustiva is an inducer of CYP3A, which means it speeds up its effect. Medications that are metabolized by CYP3A, such as propecia, may be cleared from the body more quickly when they are given along with Sustiva. Therefore, the blood level of the propecia may drop. There have been no reported studies that actually measured the effect, but this is what might be expected. It would be best to carefully monitor the combination since the expected effect would be to lower rather than raise the level of propecia.

Best, Joe