Factors Associated with Reduced Antituberculous Serum Drug Concentrations in Patients with HIV-TB Coinfection

We describe correlates of reduced antituberculous serum drug concentrations (SDCs) in HIV-infected patients receiving treatment for active tuberculosis (TB). Cross-sectional analysis of individuals diagnosed with HIV and active TB in Northern Alberta, Canada, was performed. Of the 30 HIV-TB cases, 27 underwent measurement of SDCs. Rates of low SDCs were 9 of 26 (34%) for isoniazid (INH) and 16 of 25 (64%) for rifamycins. Increased weight and elevated body mass index (BMI) correlated with low SDCs for rifampin (P < .05) and increased weight also correlated with reduced SDCs for INH (P < .05). This suggests that conventional antituberculous dosing may be too low and consideration should be given to increase the maximum initial weight-based doses in HIV-infected patients.