Use of in vitro models to study the emergence of resistance

1. Use of in vitro models to study the emergence of resistance Professor Inga Odenholt Department of Infectious Diseases University hospital, Malmö Sweden

2. The university hospital in Malmö

4. How to study the emergence of resistance? • In vitro with static concentrations (MPC concept) • In in vitro kinetic models with fluctuating concentrations • In in vitro foreign body kinetic model • In animal models • In human clinical trials

5. Different types of in vitro kinetic models • Diffusion models • Two compartment models • Dilution models, • without filter-membranes • with filter-membranes

6. The study of enoxacin to determine the Cmax/MIC ratio for bactericidal activity and emergence of resistance Blaser et al.AAC :31;1054-60, 1987

7. Diffusion model

8. The concentration of enoxacin given as 500 mg BID or 1000 mg OD

9. Resistence was studied by population analysis and by inoculating the bacteria on antibiotic containing plates 0.33, 1 and 3 mg/L In conclusion: A Cmax/MIC > 8 was needed to prevent regrowth

10. The efficacy of enoxacin against P. aeruginosa with a MIC of 1 mg/l

11. Dose ranging and fractionation of ciprofloxacin against P. aeruginosa Marchbanks et al.AAC:37:1756-63, 1993

12. Hollow fiber cartridge

13. Marchbanks etal. AAC 1993

14. Killing of P.aeruginosa at three different dosage regimens of ciprofloxacin Marchbanks et. Al. AAC 1993

15. Initial MIC=1 mg/l. Sampled at 24 h

16. Dilutions models

17. II. Dilution model with filter-membrane Löwdin et.al AAC, 40: 2478-2482, 1996

19. C=Co x e-kt K= the rate of elimination Co= the concentration in the vessel at time 0 K=F/V F=V x 0.693/t1/2

20. Pharmacodynamics of Penicillin G vs S. pneumoniaewith different susceptibility for penicillin Odenholt et al AAC; 47:518,2003

21. T>MIC PSP 46% PIP 6% PRP 0%

22. T>MIC PSP 75% PIP 38% PRP 0% T>MIC PSP 100% PIP 100% PRP 48%

23. Cmax Serum or tissue drug concentration MPC Mutant Selection Window MIC Time post-administration The concept of Mutant Selective Window

24. Emergence of resistant S. pneumoniae exposed to moxifloxacin inside and outside the MSW Zinner et al. JAC, 2003:52

25. Selection of ciprofloxacin resistance in E. coli Olofsson et al. JAC;57:1116-21, 2006.

26. Methods • 2 quinolone susceptible strains (ATCC and Nu 14) and one gyr A mutant (nu 118) • The MPC was 16xMIC for the susceptible strains and 4 x MIC for NU 118.

27. Ciprofloxacin concentration fixed at MPC for different time points. T>MPC for 18 h was needed to prevent growth of resistant bacteria

28. A Cmax of 64xMIC was needed to prevent growth of resistant bacteria for both susceptible strains (64xMIC)

29. Selection of resistant mutants from Nu 14 (MIC=0.008 mg/l) as a function of Cmax

30. Results • T>MPC of 18 h was sufficient to prevent selection of resistance • A Cmax of 64xMIC was needen to prevent selection for the susceptible organisms (8 x MIC for Nu 118). • The parameter best predicitve of emergence of resistance was AUC/MPC

31. Synergy of colistin with rifampin and trim/sulpha against multi-resistant S. maltophilia Giamarellos et al. Diag Microb Inf Dis 44:259-63, 2002

33. Regrowth was noted at 24 h when the strain was exposed to colistin alone at 1 and 4 xMIC • Even though the strain of S. maltophilia was resistant to rifampin, regrowth was prevented at 24 h.

34. Minocycline + colistin against imipenem-resistant A. baumannii Yen Tan et al. JAC July, 2007

36. Neither minocycline or colistin alone demonstrated bactericidal activity. Regrowth appeared at 6 hs. • However, the combination was synergistic and bactericidal

37. Thank you for your attention