1 / 34

Animal Efficacy Studies for Antitubercular Agents

Animal Efficacy Studies for Antitubercular Agents. V. Balasubramanian. ASTRAZENECA R&D BANGALORE, INDIA. Some questions…. Do we need animal model(s) for determining antitubercular efficacy? Is the determination of blood levels sufficient to predict the outcome against infection?.

micheal
Download Presentation

Animal Efficacy Studies for Antitubercular Agents

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Animal Efficacy Studies for Antitubercular Agents V. Balasubramanian ASTRAZENECA R&D BANGALORE, INDIA

  2. Some questions…... • Do we need animal model(s) for determining antitubercular efficacy? • Is the determination of blood levels sufficient to predict the outcome against infection?

  3. Some generalizations….. • Drug Class In vitro mode in vivo efficacy • of killing parameter • b-lactams Time dependent T > MIC • Aminoglycosides Concentration dependent AUC/AUIC ratio • Fluoroquinolones Concentration dependent AUC/AUIC ratio • Macrolides Time dependent AUC [half-lives and PAE high] • T > MIC [half lives and PAE low]

  4. Pharmocokinetic Properties of Anti-mycobacterial Drugs Drug [mg/kg] MIC Cmax Fold T1/2 T > MIC [ug/ml] [ug/ml] [h] [h] Isoniazid [25] 0.02 7 350 2 18 Rifampicin [25] 0.1 10 100 3.5 28 Rifabutin [25] 0.05 10 200 45 10 d Rifapentine [25] 0.02 15 750 13.2 5 d Pyrazinamide [100] 6 30 5 10 36 Ethambutol [100] 2 4 2 3 6

  5. Pharmocokinetic Properties of Anti-mycobacterial Drugs Drug [mg/kg] MIC Cmax Fold T1/2 T > MIC [ug/ml] [ug/ml] [h] [h] Ethambutol [100] 2 4 2 3 6 Ethionamide [100] 1 2 2 2 4 Streptomycin [200] 0.5 3 6 2 8 Amikacin [200] 1 30 30 2 12 Kanamycin [200] 6 30 5 2 6 Sparfloxacin [50] 0.12 2.8 5.6 5 18 Ofloxacin [200] 1.0 10 20 7 35 Linezolid [50] 17.7 1.4 PNU-100480 [50] 7 0.7

  6. ED50 [mg/kg] Isoniazid (H) 2.7 - 3.4 Rifampicin (R) 4.5 - 6.5 Ethambutol (E) 35 - 55 Ethionamide (A) 75 - 107 Streptomycin (S) 75 - 108 Effect of Chemotherapy on Survival - Kradolfer et al • Design • Intravenous infection with M. bovis Ravenal strain • Oral administration of drugs - day 11 & 12 post infection (Sm - s.c.) • Minimal effect: Prolonging the survival of 50% mice in the treated groups - ED50 H R E A S Data from: Kradolfer, F. 1970. Antibiotica et Chemotherapia. 16:352-360

  7. Bactericidal Effect of Chemotherapy - Kradolfer et al • Design • Intravenous infection with M. bovis Ravenal strain • Bactericidal effect: Culture negativity after prolonged oral treatment Ref: Kradolfer, F & Schnell, R. 1971. Chemotherapy. 16:173-182

  8. Bactericidal Effect: An Initial Measure for Comparison Iv infection (~107 cfu); treatment by gavage started 1 wk pi., for 4 wks. Isoniazid, Rifamycins Oxazolidinones • Cynamon, M. H., Klemens, S. P., Sharpe, C. A., Chase, S. 1999. A. A. C. T. 43:1189-1191 • Klemens, S. P., Grossi, M. A., Cynamon, M. H. 1994. A. A. C. T. 38: 2245-2248

  9. Bactericidal Effect: An Initial Measure for Comparison Iv infection (~107 cfu); treatment by gavage started 1 day pi., for 4 wks. Aminoglycosides & Quinolones • Baohong Ji, Lounis, N., Truffot-Pernot C., Grosset, J. 1995. A. A. C. T. 39: 1341 - 1344 • Lounis, N., Baohong Ji, Truffot-Pernot C., Grosset, J. 1997. A. A. C. T. 41: 607 - 610

  10. iv infection (~105 cfu) iv infection (~107 cfu) Bactericidal Effect: Infection Dose As a Variable Treatment by gavage started 1 day pi., for 4 wks. • Miyazaki, E., R. E., Bishai, W. R. et al. 1999. A. A. C. T. 43: 85-89

  11. PK Parameters Significant bactericidal activity in mice H >>> Z > Emb > Eth [Cmax, T > MIC] H > Z > Emb > Eth Rfp = Rlz = Rbu> Rif [Cmax, T > MIC] Rlz = Rfp > Rbu > Rif Ami > Sm = Kan [Cmax] Ami > Sm = Kan Spar > Lev = Ofla [Cmax] Spar > Lev = Ofla H > Linezolid > PNU100480 [?] H > PNU100480 > Linezolid No single parameter can independently Rlz = Rfp > Rbu > Rif = Spar > H predict across drug classes H > PNU100480> Lin > Z Z = Ofla > Emb > Eth

  12. Markers Factors • Early Bactericidal Activity • Sputum Conversion • Emergence of resistance • Relapse Rates • Combination Regimen • Duration of Rx • Frequency of Dosing Clinical Efficacy in Tuberculosis

  13. Inh, Rif, Emb 108 107 106 105 Cfu/ml in sputum Pza 104 103 Rif 102 2 4 6 Time (months) Why combination is needed and why is it at least six months long? [Early Bactericidal Activity] [Sterilizing Activity]

  14. Early Bactericidal Activity [EBA] Sterilizing Activity Cfu from sputum for 1st 2 days after onset of treatment Relapse rates, 30 mo. after onset of treatment Measured by Importance Community Individual Drug Isoniazid +++ + Rifampicin ++ +++ Pyrazinamide + +++ Ethambutol + - Streptomycin + -

  15. Model for the Initial and Continuation Phases of Rx iv infection (107 cfu/animal) Rx: Oral gavage started 14 days pi. Initial Phase Log10 cfu /spleen Spontaneous Relapse [once daily for 2 months] (6 mo. post) Untreated 0 6.65 ± 0.19 Inh+Rif 25 + 10 3.00 ± 0.54 Rif+PZA 10 + 150 0.86 ± 0.44 *Inh+Rif+PZA 25 + 10+ 150 2.79 ± 0.73 Continuation Phase% mice with [once daily for 4 months] +ve spleen cultures *+* 25+10+150 0 35% *+Inh+Rif 25+10 0 38% *+Rif+PZA 10+150 0 9% Ref: J. Grosset, Truffot-Pernot, C., Lacroix, C., Ji. B. 1992. A.A.C.T. 36: 548-551

  16. Spleen Lungs Inh+Rif Inh+Rif+Pza Inh+Pza+Rfp 7/7 6/7 0/8 7/7 7/7 3/8 7/7 6/7 0/8 7/7 7/7 3/8 Shortened Course - Daily Treatment with Rifapentine Ref: Cynamon, M. H. et al. 1999. A. A. C. T. 43: 2356-2360

  17. Rifr mice 61% 47% Intermittent treatment with Rifapentine iv. infection ~107 cfu / animal Rx 8 weeks Rx 12 weeks Grosset J. et al. 1998. Am J Respir Crit Care Med. 157:1436-1440 Cynamon, M. H. et al. 1999. A. A. C. T. 43: 2356-2360

  18. Prophylaxis 0 28 44 100 128 8 wk 12 wk BCG Infection Dosing Ref: Jabes, D., Bruna, C. D., Rossi, R., Olliaro, P. 1994. A. A. C. T. 38:2346-2350 *

  19. Wks. 2 9 15 23 26 32 35 Inh+Pza 7 wks Test Rx 6 wks Cort 3 wks Cort 3 wks Infect iv 8.8x105 Sac Sac Cornell Model for Effect on Reactivation Disease • Question: After the initial phase, what confers sterilization? • Test regimens were R [15mg/kg]; RH [H25]; RZ [Z150]; RHZ • % positive organs : R 81; RH 63; RZ 65; RHZ 71 [p = 0.3] • However, trend chi-square suggested than addition of H or Z improved the sterilization effect of R • Answer: At least in the Cornell model, none of the existing regimens confer complete sterilization Ref: Dhillon, J., Dickinson, J. M., Sole, K., Mitchison, D. A. 1996. A. A. C. T. 40: 552-555

  20. 0 12 16 34 41 44 48 Inh+Pza 12 wks No Rx Test Rx 18 wks No Rx No Rx Cort Infect iv 3.95x105 Culture -ve organs Sac Cornell Model for Effect on Reactivation Disease Treatment Dosing % Positive Log10cfu Log10cfu organs spleen lungs Placebo 100 3.24±2.2 5.77±0.11 Inh 25 daily 50 1.93±2.11 0.71±1.34 Rif 10 twice weekly 100 4.11±0.40 5.39±0.49 Rpt 10 once weekly 100 3.63±1.18 4.67±2.35 Inh+Rpt once weekly 37.5 1.46±2.04 1.78±2.49 Ref: Miyazaki, E., Chaisson, R. E., Bishai, W.R. 1999. A. A. C. T. 43:2126-2130

  21. Rifapentine • Animal Data • Daily dosing with Rfp offers the possibility of reduced Rx. • However, due to long half life, possibility of accumulation • Based on animal studies, twice weekly better than once weekly • Based on daily dosing in animals, HZRfp > HZRif (relapse rates) • However, relapse rates not determined in the case of intermittent Rx!) • Intermittent Rfp approved by FDA in 1988 (1st in >15 yrs for TB) • Clinical Trial data (surprises!) • 2HRZ/4H2R2 better than 2HRpZ/H1Rp1, based on relapse data • 4/5 HIV+ patients in 2HRpZ/H1Rp1 developed Rifres Ref: Vernon, A. et al. 1998. Am. J. Resp. Crit. Care. Med. 157: A467

  22. Peritoneal 3.7% 14.6% Meningeal 4.2% Bone/Joint 8.5% Other 9.3% Miliary 9.8% Tuberculosis Genitourinary 16.0% Pulmonary 84.5% Pleural 21.5% Lymphatic 27.0% ROUTE OF INFECTION AS A VARIABLE • Infection RouteIntravenousRespiratory • Infection Dose 106 cfu/animal10 cfu/animal • Quantitationcfu / spleencfu / lungs • Infrastructure SimpleSpecialized

  23. Infect with M. tuberculosis 84 14 Model for Evaluating Primary Efficacy Respiratory Challenge (10 cfu / animal) Intravenous Challenge (106 cfu / animal) Log10 cfu / lungs Time (days)

  24. Combination Rx in the Respiratory Infection Model Log10cfu / organ Days • Resp infection (100 cfu / animal) • Once a week oral Rx • Brooks, J & Orme, I. 1998. • A. A. C. T. 42: 3047-3048 35 Similar results 1/wk; 5 wks (resp) vs 6/wk;12 wks (iv)

  25. Infect with M. tuberculosis Test 3wk. RZ:8wk 1wk Model for Evaluating Sterilization [20 wk. assay]

  26. Bactericidal Effect Determined in Guinea Pigs Ref: Smith, D. W., Balasubramanian, V., Wiegeshaus, E. H. 1991. Tubercle. 72:223-2310

  27. Towards clinical use... Compounds exhibiting statistically significant reduction in cfu • Rlz = Rfp > Rbu > Rif = Spar > H • H > PNU100480 > Lin > Z = Ofla = Lev • Z > Emb > Eth • All significantly better than untreated control PK predictive of efficacy within but not across Culture negativity • No drug given singly • HRZ > HR > RZ > HZ • RE, RS, HE, not effective • Limitation: poor thera. Index • Not predictable from PK/PD Relapse rates 2HRZ/4RZ > 6HRZ > 2HRZ/4HR [8%] [34%] [38%] • In humans 2HRZ/4HR = 6HRZ [~8%]. • 2HRZ/4RZ not given due to Z toxicity Clinical Trial?

  28. Humans Expt. animals • EBA • Sputum conversion • Drug resistance • Relapse rates @ 30 mo. • Duration of Rx • Frequency of Rx • ?? • Rate of culture negativity • Resistance of survivors • Relapse rates @ 6 mo. • Time to culture negativity + relapse rates @ 6 mo. • PK profiles such as T1/2 Clues from Animal Efficacy for Clinical Efficacy

  29. Efficacy Models During the Course of Development • Effect (singly or combination) during early phase of infection • Survival • Bacterial counts • Spontaneous Relapse after initial and continuation phase • Reactivation following immunosuppression - Cornell • Prophylaxis • Effect on immunocompromised hosts • All of the above in animals infected via the airway will be more efficient and relevant

  30. Summary of important variables for the different efficacy models Variables Bactericidal effect Spontaneous relapse* Vaccination - - Vaccination-infection interval - - Route of infection i.v. or resp i.v. or (resp) Infection inoculum ~107cfu or 100 cfu ~107cfu or (100 cfu) Infection-Drug interval 2-4 weeks 2-4 weeks Duration of initial treatment 8 wks (iv); 2 wks (resp) 8 wks; (4 wks) Duration of continuation Rx - 16 wks; (8 wks) Duration of immunosuppression - - Post treatment interval 1 day 1 day, 3 & 6 months Measure of efficacy Cfu / spleen or lungs Cfu / spleen or lungs % mice with +ve organ cultures *conditions shown in parentheses not yet established

  31. Summary of important variables for the different efficacy models Variables Sterilization* Prophylaxis Vaccination - BCG Vaccination-infection interval - 4 weeks Route of infection i.v. or (resp) i.v. or resp Infection inoculum ~107cfu or (100 cfu) ~107cfu or 100 cfu Infection-Drug interval 2-4 weeks 2-4 weeks Duration of initial treatment 12 weeks 8-12 weeks Duration of continuation Rx 12 weeks - Duration of immunosuppression 3 weeks - Post treatment interval 1 day, 2-4 weeks 1 day Measure of efficacy Cfu / spleen or lungs Cfu / spleen or lungs % mice with +ve organ cultures *conditions shown in parentheses not yet established

More Related