We found that patients who used rifampicin-based regimens had a higher mortality rate, even though not confirmed in multivariate analysis. One hypothesis to explain such observation is the possibility of multidrugresistant tuberculosis (MDR-TB). However, culture and sensitivity test to antituberculosis drugs were not routinely performed, so we could not estimate the prevalence of MDR-TB in our sample. On the other hand, uncertain enteric absorption in critically ill patients [23] and subtherapeutic serum levels of rifampicin, especially in HIV-positive population [24, 25] , have been reported [26] [27] [28] . Drug interactions among antituberculosis drugs and HAART are also important factors to be considered. In addition, low serum albumin levels could impair drug absorption and was associated with low rifampicin and ethambutol concentrations [29] . Whereas the great majority of our study sample is composed by HIV-positive patients and hypoalbuminemia was a prevalent finding, it is possible that some patients had low serum rifampicin levels that went undetected.