Background. The pharmacokinetics of rifampin and ethambutol in HIV-infected patients with tuberculosis (TB) are incompletely characterized. We examined the pharmacokinetics of rifampin and ethambutol in a cohort of patients with HIV-related TB who were treated in the United States. Methods. Serum drug concentrations were determined 2, 6, and 10 h after dosing in 36 HIV-infected patients with TB who were taking rifampin and in 49 who were taking ethambutol. Observed serum concentrations were compared with published normal ranges and published data. Results. With daily dosing of rifampin (600 mg), 26 (77%) of 34 patients (95% confidence interval [CI], 59%-89%]) had a low maximum concentration of rifampin (<8 μg/mL), and 12 (35%; 95% CI, 20%-54%) had a very low maximum concentration (<4 μg/mL). With intermittent rifampin dosing (600 mg), 13 (68%) of 19 patients (95% CI, 44%-85%) had a low maximum concentration of rifampin, and 5 (26%; 95% CI, 11%-50%) had a very low maximum concentration. With daily ethambutol dosing (20 mg/kg), 33 (69%) of 48 patients (95% CI, 55%-81%) had a low maximum concentration of ethambutol (<2 μg/mL), and 18 (38%; 95% CI, 24%-53%) had a very low maximum concentration (<1 μg/mL). With intermittent ethambutol dosing (50 mg/kg twice weekly or 30 mg/kg thrice weekly), 13 (72%) of 18 patients (95% CI, 47%-88%) had a low maximum concentration of ethambutol (<4 μg/mL), and 5 (28%; 95% CI, 12%-54%]) had a very low maximum concentration (<2 μg/mL). Conclusions. In HIV-infected patients with TB who are receiving rifampin and ethambutol, low maximum concentrations of rifampin and ethambutol were common. For patients with HIV-related TB, therapeutic monitoring of rifampin and ethambutol levels may help clinicians achieve target serum concentrations.
Bibliographical noteFunding Information:
Financial support. Adult AIDS Clinical Trials Group, funded by the National Institute of Allergy and Infectious Diseases (1U01AI46370, UO1A127673, A12015802, A6201, A1802, A5802, A2205, AO603, A5901, A1701, A2503, IUO1A13844, PHS NCRR MO1 RR05096, and AI 38855). Potential conflicts of interest. All authors: no conflicts.