Primary Objectives:

1) To determine the proportion of patients with HIV-related tuberculosis who have abnormal pharmacokinetic parameters for isoniazid and rifabutin.

Secondary Objectives:

1. To determine risk factors for abnormal pharmacokinetic parameters for isoniazid and rifabutin.
2. To evaluate the correlation between pharmacokinetic parameters of isoniazid and rifabutin and the occurrence of toxicity attributed to antituberculous therapy.
3. To evaluate the correlation between pharmacokinetic parameters of isoniazid and rifabutin and the efficacy of TB therapy.
4. To define and correlate phenotypic INH acetylator status with the results of genotypic acetylator data obtained in the parent trial.

This study will seek to enroll every eligible patient enrolled in TBTC Study 23. Consenting patients will be asked to undergo measurements of isoniazid (if receiving), rifabutin and 25-OH desacetyl rifabutin levels at a time point in the study when steady state rifabutin levels are expected to have been achieved (at least two weeks following the start of rifabutin).

Inclusion:

1. Patient enrolled in TBTC Study 23
2. Informed consent

Exclusion:

1. Severe anemia (Hct <25%)