 Cell pellets from PK sampling once will be combined and stored for a DNA extraction, amplification, and gel electrophoresis. The genotype analysis will be completed one time per study participant. All subjects receiving INH will be genotyped for NAT2. All subjects receiving NVP will be genotyped for CYP 2B6. These genotypes will be used as covariates in the population PK analyses of NVP and INH to determine their impact on CLF clearance apparent. 