1. Role(s) of EBA Studies – Substitute for Dose Ranging JL Johnson, MD Case Western Reserve Univ

2. Mitchison. Thorax 1950;5:144 Quantitative Culture in Response to TB Treatment

3. Nairobi EBA Study 27 regimens of single drugs or combinations Sputum cfu on day -2, -1, 2, 4, 6, 8, 10, 12, 14 days Day 0-2 mean decrease in cfu 0.422 logs Day 2-14 mean decrease in cfu 0.129 logs Jindani. ARRD 1980;121:939

4. Fall in CFU during Chemotherapy  cfu 0-2  cfu 2-14 Nil-0.02 H 3000.720.11 R 10 per kg0.190.10 S 1g0.090.13 E 25 per kg0.250.16 Z 2g0.040.11

5. Nairobi EBA Study First 2 days of therapy - significant differences identified between drugs Days 2-14 differences between drugs was smaller & less frequently statistically significant ARRD 1980; 121: 939; AJRCCM 2003; 167: 1348

6. Bacillary Killing During Early Treatment Phase 1 (Day 0-2) Rapid, exponential killing of rapidly dividing organisms. Rate determined by action of drug on log phase bacilli Phase 2 (Day 2 and beyond) – killing of slowly dividing bacilli; sterilizing action of drugs; rate determined by bacterial metabolism & rapidity of action of drug(s)

7. Response to TB Treatment

8. EBA EBA = EBA 0-2 – penetration into lesions & bactericidal action against rapidly dividing bacilli Extended EBA = EBA 2-7 – rough estimate of possible sterilizing activity

9. EBA for Current Drugs S. African MRC EBA Studies DRUGEBA 0-2EBA 2-5 INH0.600.06 OFL0.390.17 EMB0.25 RMP0.200.30 CIP0.21 STM0.13 RBT0.08 AMIK0.05 PZA0.003

10. EBA in Different Studies DrugStudyEBA INHJindani ’800.72 Chambers ’980.60 Gosling ’030.77 Dietze ’050.67 RMPChan ’920.29 RMPSA MRC0.20 RBTChan ’920.05 RBTSA MRC0.08 CIPROKennedy ’930.20 CIPROSA MRC0.21 OFLOChambers ’980.32 MXFGosling ’030.53

11. Sources of Variation between Patients in the Same EBA Study EBA unrelated to age, sex, weight, HIV status EBA correlated w/ radiographic severity of disease, cavitary disease in 2 studies

12. Source of Variability in EBA Studies In 8 studies from S Africa, overall variability was 0.03 log 10 cfu/ml/day –due to laboratory processing 0.0011 –due to pt characteristics & sputum collection 0.0212 EBA is reproducible; greatest source of variation is interpatient variation due to disease characteristics & sputum sampling

13. Risk of Acquired Drug Resistance in EBA Studies Not examined carefully in all studies, but appears to be low Only 1 pt in studies to date (over 880 patients)

14. Need for Untreated Nil Group Weighted mean EBA 0-2 for nil in 9 studies was 0.00036 Can test drug arms vs. zero. Should measure pretreatment cfu for 2 days for pts Sirgel. J Antimicrob Chemother 2001;47:177.

15. Need for INH Comparator Group Mean EBA 0-2 for INH 300 was 0.575 (95% CI 0.515-0.636) INH 300 arm useful as positive comparator & to assess whether assay is working Sirgel. J Antimicrob Chemother 2001;47:177.

16. Contemporary EBA Study Design 1.Newly Dx, sputum smear + TB; 10-12 pts per arm 2.No recent Rx w/ drugs w/ known anti-TB activity 3.Pts w/ severe TB (miliary, meningeal) excluded 4.Treatment w/ monotherapy for up to 7 days acceptable to IRBs, then all treated w/ std chemotherapy

17. Contemporary EBA Study Design 5.Able to produce adequate amounts of sputum 6.Daily overnight sputum collections w/ 2 pretreatment collections 7.INH 300 comparator group useful 8.PK sampling 9.Pre- and post-Rx drug susceptibility

18. Types of Trials

19. Use in Dose Ranging

20. Example of possible use of EBA (0-2) to identify doses to be further evaluated Donald. AJRCCM 1997;156:895

21. EBA 0-2 of INH, Rifampicin and Streptomycin Sirgel. AJRCCM 2005;172:128.

22. EBA - RMP & Rifapentine Sirgel. AJRCCM 2005;172:128

23. Use in Comparing Different Drugs in a Class

24. EBA Day 0 to 2 95% CI for Mean Drugn Mean EBA SD Lower Bound Upper Bound INH Levo Gati Moxi 10 0.67 0.45 0.35 0.33 0.17 0.35 0.27 0.39 0.55 0.20 0.15 0.05 0.80 0.71 0.54 0.62

25. EBA Day 2 to 7 95% CI for Mean Drugn Slope B2-7SD Lower Bound Upper Bound INH Levo Gati Moxi 9 10 9 0.14 0.24 0.27 0.24 0.16 0.12 0.10 0.11 0.02 0.15 0.20 0.11 0.27 0.33 0.34 0.37

26. Use in Evaluating Combinations

27. Fall in CFU during Chemotherapy  cfu 0-2  cfu 2-14 H 3000.720.11 SH0.510.07 EH0.700.05 RH0.710.22 HZ0.490.10 Am Rev Respir Dis 1980;121:939

28. EBA of Drug Combinations Am Rev Respir Dis 1980;121:939

29. What Might Be Learned from Combination EBA Studies? Drug-drug interactions Synergy vs antagonism vs indifference Increased toxicity

30. Two Drug Combination EBA 1-78-14 > HRZE XH HRZE XR HRZE XZ HRZE XEXSHRZE

31. EBA Method - Advantages Reproducible; small # of pts required Can detect significant differences between drugs during the initial days of administration Drugs can be compared with one another Different doses can be evaluated to define dose for phase 2b & 3 trials PK can be compared to bactericidal activity Short term toxicity in humans with TB can be evaluated

32. EBA - Disadvantages May not tell us much about sterilization by a drug or regimen as later measurements. Not useful for some drugs. Rifampin & PZA have little & no EBA but are best current sterilizing drugs. Less valuable for comparing regimens particularly in combination w/ INH Little experience w/ EBA of drugs that accumulate or are given infrequently

33. EBA Study of New Drug Evaluate highest tolerable dose based on initial toxicology data If EBA 0-2 less than 0.2, further EBA studies unlikely to be helpful If EBA 0-2 significant, conduct dose ranging studies to define therapeutic margin Do PK sampling of all subjects