2. Population PK/PD analysis of the bactericidal activity of sutezolid and its major metabolite against intracellular Mtb in whole blood cultures of TB patients Tong Zhu 1, Sven Friedrich 2, Andreas Diacon 2, and Robert Wallis 1 1 Pfizer, Groton CT; 2 Stellenbosch University, Cape Town, South Africa

3. Sutezolid First oxazolidinone developed for TB Parent: PNU-100480 or U-480 Metabolite: PNU-101603 or U-603 MICs are similar when tested on agar After oral dosing, plasma concentrations of metabolite are several fold higher than parent Louie & Drusano found killing of extracellular Mtb in hollow fibers mainly due to the metabolite Converse & Nuermberger found killing of intracellular Mtb in cell culture models mainly due to the parent

4. Objective To develop a PK/PD model describing the relative contributions of sutezolid and its metabolite against intracellular Mtb in vivo in patients with pulmonary tuberculosis.

5. Methods Data (plasma concentrations of U-480 and U-603, and corresponding whole blood bactericidal activity [WBA]) came from patients treated with sutezolid 600 mg BID (N=25) or 1200 mg QD (N=25) enrolled the sutezolid EBA trial (B1171003). A 4 parameter sigmoid curve was used to describe the concentration-activity relationship, based on prior observations that killing was concentration-dependent at low concentrations, but did not increase further once a maximal response (Imax) was reached. The activities of U-480 and U-603 were assumed competitive, based on prior observations that U-603 did not further increase the activity of optimal concentrations of U-480.

6. Equations Predicted result Value in the absence of drug Maximal effect Fraction of IC 50 Shape (Hill) factor Dilution factor

7. Data set 690 PK and 345 WBA determinations at 0, 1, 2, 3, 6, 8, and 12 hrs post dose measured on days 13-14 The median ratio of U-603/U-480 plasma concentrations was 7.1 (range, 1 to 28). High ratios mainly occurred at late time points in the dosing interval. The wide range of values facilitated modeling of the relative contributions of parent and metabolite.

8. Diagnostic plots

9. Parameters ParameterEstimate90% CI Fixed effects WBA 0 0.1820.154 to 0.209 I max 0.5970.559 to 0.636 IC 50 480 ng/mL70.456.0 to 84.9 IC 50 603 ng/mL1200839 to 2960  480 2.251.7 to 3.2  603 (0.94)- Random effects WBA 0 (%)27.419.4 to 35.2 Sigma (%)31.027.4 to 33.8 17x 2x

10. Predicted drug activity (in vitro) 11x

11. Predicted drug activity (in vivo) Discrete timepoints Cumulative activity 80% of activity due to parent BID superior to QD

12. Conclusions Killing of intracellular Mtb by oral sutezolid is mainly due to the parent, despite the higher plasma concentrations reached by the metabolite. Intracellular drug accumulation may account for this Mtb subpopulations have distinct roles in TB: Extracellular: resistance and treatment failure Intracellular: persistence and relapse Factors that differentially affect exposure to parent and metabolite (e.g., dosing schedules, induction of metabolism) may have different effects on these 2 outcomes.