<qa>  What is the relationship between rifapentine exposure and response by time to conversion inAn important knowledge gap in TB clinical trials is how to efficiently and economically assess new drug efficacy, as biomarkers now commonly used in phase 2 trials have had varying success in predicting drug efficacy in phase 3 trials. However, optimal use of a drug can be achieved through population pharmacokinetic-pharmacodynamic PKPD studies that combine pharmacokinetic properties of a drug and efficacy outcomes of treatment. In TBTC Study 29-29X PKPD, the relation between rifapentine exposure and response by time to conversion in sputum cultures was established. 