The purpose of the study is to look at whether changing directly from one medication for HIV
(efavirenz) to a new medication for HIV (TMC125) has any effect on the levels of TMC125 in
the blood, compared to when TMC125 is taken without efavirenz having been taken immediately
beforehand.
The study aims to help the investigators understand whether it is safe to change directly
from efavirenz to TMC125 (with no gap between the treatments) in patients who need these
treatments.
The study will investigate the blood levels of TMC125 when it is taken both once and twice a
day.