Antiretroviral therapy regimens containing efavirenz (600 mg per day) were less compromised by concomitant use of rifampicin than were those that contained nevirapine (400 mg per day) in patients with concurrent HIV-1 infection and TB. Low drug exposure and low body weight are important predictive factors for treatment failure.

Nevirapine-based ART is an option for HIV-infected patients who receive rifampin in resource-limited countries or those who cannot tolerate efavirenz.

Seventy-one human immunodeficiency virus-infected patients with tuberculosis who were receiving a rifampin (rifampicin)-containing regimen were initiated on treatment with efavirenz at 600 mg/day plus stavudine-lamivudine. Fasting efavirenz concentrations at 12 h after dosing (C 12 ) were monitored. The mean ؎ standard deviation efavirenz C 12 at weeks 6 and 12 and after rifampin discontinuation were 4.5 ؎ 4.3, 3.8 ؎ 3.5, and 3.5 ؎ 2.7 mg/liter, respectively. High body weight was associated with a low efavirenz C 12 at weeks 6 and 12 (P ‫؍‬ 0.003, r ‫؍‬ ؊0.255). The efavirenz C 12 regression prediction line at 1 mg/liter intercepted a mean body weight of 57.5 kg.N 2 R was a randomized clinical trial comparing the clinical efficacies of two nonnucleoside reverse transcriptase inhibitorbased highly active antiretroviral therapy (HAART) regimens for patients coinfected with human immunodeficiency virus (HIV) and tuberculosis who received rifampin (rifampicin) (9). A secondary objective was to assess body weight as a cutoff for selecting the daily dosage of efavirenz. Patients were enrolled and followed through 60 weeks after HAART. Inclusion criteria were described previously (9). All patients were started on twice-daily stavudine-lamivudine and efavirenz at 600 mg/day at bedtime. The dosages of rifampin were 450 mg/ day for body weights of Յ50 kg and 600 mg/day for body weights of Ͼ50 kg. Fasting efavirenz concentrations at 12 h after dosing (C 12 ) were measured with a validated highperformance liquid chromatography assay at weeks 6 and 12 and at 6 to 12 weeks after rifampin discontinuation. This assay was developed at the Department of Clinical Pharmacology of the University Medical Center Nijmegen, Nijmegen, The Netherlands (5).All statistical analyses were performed with SPSS version 11.5 (SPSS Inc., Chicago, IL). Pearson's correlations were used to study the relationships between parameters. Factors possibly predictive of efavirenz C 12 and an elevated serum alanine aminotransferase (ALT) activity at week 12 were evaluated with a linear-regression model. Inter-or intrapatient variability was expressed as a coefficient of variation (CV). The institutional ethics committees of the Bamrasnaradura Infectious Diseases Institute and the Thai Ministry of Public Health approved this study.Seventy-one patients were enrolled; 65% were male, and the mean Ϯ standard deviation (SD) baseline body weight was 53 Ϯ 10 kg. The mean Ϯ SD baseline CD4 cell count was 75 Ϯ 68/l, the median (interquartile range) log plasma HIV type 1 RNA copy number was 5.8 (range, 5.6 to 5.8), and the mean Ϯ SD serum ALT activity was 29 Ϯ 18 U/liter. Six (8.5%) patients were positive for hepatitis B surface antigen, and 18 (25.4%) were positive for hepatitis C antibody. The mean Ϯ SD efavirenz C 12 at weeks 6 and 12 and after rifampin discontinuation are shown in Fig. 1. After stratification into four groups by body weight (35 to 45, 46 to 55, 56 to 65, and Ͼ66 kg) at week 6, the mean C 12 were 7.6 mg/liter, 4.1 mg/liter, 2.4 mg/liter, and 1.8 mg/...