 An 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. 