1. Overview on determination of ECOFF, PK/PD breakpoints ,clinical cut-offs and the setting of Clinical breakpoint by VetCAST
VMAS symposium/workshop
Uppsala December 2017
Pierre-Louis Toutain,
Royal Veterinary College,
London & National Veterinary School of Toulouse, France

2. Objectives of the presentation
To explain how VetCAST expect to establish veterinary clinical breakpoints
As a subcommittee of EUCAST, VetCAST will follow the general procedure implemented by EUCAST Based on its SOP ,
Position paper
“En route towards European Clinical Breakpoint for veterinary antimicrobial susceptibility testing: the VetCAST approach”

3. 1-What is VetCAST

4. VetCAST is a Subcommittee of EUCAST

5. Acronyms EUCAST CLSI CLSI/VAST
European Committee on Antimicrobial Susceptibility Testing
CLSI
The Clinical and Laboratory Standards Institute
CLSI/VAST
Sub-committee of CLSI dealing with the susceptibility testing of veterinary pathogens and determination of veterinary CBP

6. 2-What is the mission of VetCAST

7. To establish CBP
ECOFF
COCL
PK/PD BP

8. Definitions Cut-off Clinical breakpoints (CBP)
the values of MIC (mg/L) selected by an ad hoc committee to be used by testing laboratories to qualitatively report the results of AST as Susceptible (S), Intermediate (I), or Resistant (R). Not to be confused with cut-offs
Cut-off
A threshold value for MICs to separate two entities or targets (ECOFF, PK/PD cut-off, Clinical cut-off)

9. Definitions ECOFF Clinical cut-off
Epidemiological (bacteriological) cut-off
PK/PD breakpoint (EUCAST) or PK/PD cut-off (CLSI)
the MIC value for which a targeted PK/PD index value can be achieved with a routine dosage regimen in a given percentage of animals (usually 90%)
Clinical cut-off
Term not used by EUCAST; for CLSI, Clinical cut-off is the MIC value for which probability-of-cure can be achieved with a routine dosage regimen in a given percentage of animals

10. Terminology: EUCAST vs. CLSI/VAST
Organisation
Epidemio
PK/PD
Clinics
Decision
CLSI/VAST
COWT
COPD
COCL
CBP
EUCAST
ECOFF
PK/PD breakpoint
VETCAST
PK/PD cutoff

11. VETCAST modus operandi: A risk analysis approach
assessment
Risk management
Risk communication
Cut-offs
Clinical breakpoint
Expert rules
Science
Decision
Harmonisation

12. Development of a (clinical) Breakpoint (BP)
Diameter
Clinical BP
COWT
ECOFFs
COPK/PD
COCL

13. 3-Establishing ECOFFs Epidemiological/microbiological cut-off

14. Epidemiological cut-off values (ECOFFs)
ECOFFs are related to the distribution of MICs of wild type organisms lacking acquired or mutational resistance to the antimicrobial agent in question.
The ECOFF is essentially the upper MIC value of the wild type distribution.
EUCAST SOP 7.0

15. MIC-data available tetra/doxycycline EUCAST

17. ECOFF at VetCAST
A minimal total number of 100 MIC values in the putative wild type population for each bacterial species, originating from at least 5 accepted MIC data sets are required to define an ECOFF
Stakeholders are encouraged to send their in-house data for aggregation, after review by VetCAST, with the already published MICs

18. Methods for defining the wild type distribution (determining the ECOFF)
The “eyeball” method (Kahlmeter)
The 95% rule (Pfaller)
The Normalised Resistance Interpretation (Kronvall)
The iterative statistical method (Turnidge)
Multimodal analysis (Meletiadis)
From John Turnidge, CLSI Workshop, Tampa, January 2013

19. Ciprofloxacin & Acinetobacter baumannii

20. Statistical method for ECOFF/COWT

21. For more details

22. ECOFF at VetCAST A CBP will never lower than the ECOFF
(see rule 10.2 of the SOP 1.2 (European Committee on Antimicrobial Susceptibility Testing, 2013)
As a surrogate of CBP
Local administrations, when several CBP are required …
For surveillance
ECOFF is a parameter, not CPB

23. 3-The setting of a PK/PD breakpoint

24. The human PK/PD breakpoint reflect clinical data
AUC/MIC or T>MIC magnitude predictive of cure

25. The PK/PD breakpoint at VetCast
For veterinary medicine in the EU, reference to PK/PD concepts was only introduced in 2016 by EMA/CVMP in its latest guidance on the demonstration of efficacy of antimicrobial substances, although only for preclinical investigation (European Medicines Agency, 2016).
No clinical data regarding PK/PD as for human medicine
PK/PD will only reflect preclinical data and is equivalent to the PK/PD cut-off of the CLSI

26. The setting of a PK/PD BP
Step1
Selection of a PK/PD index predictive of clinical efficacy and/or prevention of resistance
Step 2
Determination of the critical value (magnitude) of the selected PK/PD index
Step 3
Computation , for a given animal species and for all possible (not probable) MICs of the percentage (proportion) of animals able to achieve the critical value of the selected PK/PD index (computation of so-called Probability Target Attainment (or PTA)

27. Step 1:Selection of a PK/PD index
fAUC24h/MIC
fCmax/MIC
fT>MIC
fCmax/MIC was historically seen with aminoglycosides but is now losing favour, aminoglycosides being now managed as an AUC/MIC drug class ,
Rem: it was shown that for all drugs/formulations having a long half-live that AUC/MIC is the appropriate index (AU/MIC: universal index?)

28. Rodents + clinical validation
Step 1: Determination of the best PK/PD index and of its critical value (magnitude )
PK/PD index
Default value
Experimental value
Preclinical
In vitro/In vivo
Dynamic: killing curves
In vivo
Rodents + clinical validation
Clinical

29. Dynamic: killing curves
Step 1: Determination of the best PK/PD index and of its critical value (magnitude )
PK/PD index
Default value
Experimental value
Preclinical
In vitro/In vivo
Dynamic: killing curves
In vivo
Target species
Clinical

31. Dynamic: killing curves
Step 1: Determination of the best PK/PD index and of its critical value (magnitude )
PK/PD index
Default value
Experimental value
Preclinical
In vitro/In vivo
Dynamic: killing curves
In vivo
Target species
Clinical

32. PK/PD indices critical values: Killing curves & hollow fibers test systems

33. Modeling approach of killing curve to determine PK/PD index
PD parameters
Florfenicol
EC50 (mg/L)
0.447
Emax (1/h)
2.01
Hill
2.7

34. In silico dose fractionation trials
Solving the semimechanistic PD model with PK parameters corresponding to a given dosage regimen and a given formulation, the time-development of the bacterial population can be predicted (in silico clinical trial)

35. Benzylpenicillin; ceforuxime; erythromycin; gentamicin; moxifloxacin and vancomycin
The in silico predictions based on the in vitro PKPD confirmed previously established PK/PD indices
The selection and magnitude of the PK/PD index were shown to be sensitive to differences in PK and dosing intervals.
This study supports the use of PKPD models built from in vitro time-kill curves in the development of optimal dosing regimens for antibacterial drugs.

36. AUC/MIC vs. Time>MIC to predict florfenicol effect (in silico simulations)
AUC/MIC= h for 120h
T>MIC=43-49% ( 120h)
AUC/MIC
T>MIC

37. The case of fT>MIC
For a given dose, T>MIC is dependent of the shape of the curve
influence of modalities of administration
E.g. dosage interval
Top feeding vs. pump
Influence of the formulation

38. Short (Black) vs. LA formulations (Blue) (same AUC and T>MIC=50%)
Are they equivalent in terms of T>MIC?

39. Short vs. LA formulations
Curves
T>MIC
(%)
AUC
Black 50
5000
Blue
100
10000
Magenta
6250
-----MIC
2 options: two different CBP for Blue and Magenta or alternatively to consider the AUC s

40. AUC/MIC: an universal PK/PD index for veterinary medicine?
It is quoted: For drugs like the b-lactams where the efficacy generally have been found to be correlated to T.MIC, the best PK/PD index shifts toward AUC/MIC dependence as the half-life increase, as seen in patients with a reduced renal function e.g., elderly or neonates.

41. The setting of a PK/PD CO
Step1
Selection of a PK/PD index predictive of clinical efficacy and/or prevention of resistance
Step 2
Determination of the critical value (size) of the selected PK/PD index
Step 3
Computation , for a given animal species and for all possible (not probable) MICs of the percentage (proportion) of animals able to achieve the critical value of the selected PK/PD index (computation of so-called Probability of Target Attainment (PTA)

42. What is PTA? More literally the question is:
E.g. What is the critical (maximal) MIC for which we can guarantee that plasma drug concentration will be:
above a possible MIC for X% of the dosage interval (often 50 or 80%) for fT>MIC
or≥ to a given fAUC/MIC
for the intended dosage regimen in at least 90% of subjects of the targeted population

43. PTA (Quantile) 90 with or without its 90% Confidence interval

44. What PTA target value at VetCAST?
Statistically, the PK/PD breakpoint is related to the notion of a prediction interval (PI).
The appropriate choice of percentile ( for instance 90 or 95% but surely not 50% ) has not yet been decided at VetCAST,
but VetCAST anticipates that due to the large inter-animal variability and the paucity of data, a very wide prediction interval could have large consequences for the establishment of a CBP

45. Prediction interval vs Confidence interval
A Prediction interval (PI) is a range that is likely to contain a specified proportion (e.g. 90%) of the population.
PI is a random variable and it has its own confidence interval (e.g 95 or 99%)
Same conceptual difference as between a SD and a SE

46. PTA mean vs quantiles Breakpoint for amoxicillin in pigs (CLSI)
Q_91%: 0.125mg/L
Q_59%=0.5mg/L
NO PK variability (mean): 0.5mg/L

47. How to compute PTA From already published PK parameters
The CLSI approach
From raw data (meta-analysis)
Recommended by VetCAST

48. Florfenicol in calves as an example

49. Florfenicol
Three data set
50 calves
Rich data

50. Computation of the PTA by Monte Carlo Simulations (MCS)
PK raw data From clinics & preclinical unbalanced data
Population modeling
Monte Carlo Simulation
(n=5000 animals)
PTA(%)

51. PTA using MCS
We need a model (exponential) to simulate the 5000 curves

52. Why we need a population modeling
To aggregate sparse and unbalanced data
Data collected in clinics
From different companies/lab
The only fair approach for a meta-analysis
To document covariates to generate expert comments (rules)
Formulation effect?
Breed effects?
Preruminant vs ruminant cattle ?

53. Florfenicol: Unbalanced data
Three data set
50 calves
Rich data
LOQ of 0.25 (RED) vs 0.05 (Blue and grey) µg/ml

54. Unbalanced data for florfenicol 3 data sets & 2 models!
JVPT 2011
What about T>MIC for low MIC?
Other source

55. Unbalanced data for florfenicol 2 data sets & a single POP model

56. IM administration 30mg/kg

57. Clinical cutoff

58. The clinical CO (COCL)
The COCL is based upon the collection of isolates obtained during the clinical effectiveness studies.
COCL reflects the upper limit of the MIC values associated with a high likelihood of clinical success [probability of cure (POC)].
There is no set method for establishing the COCL, and no hard target for POC.
POC=0.9
POC= Probability of cure
MIC/Dose

59. Issues for to determine the clinical cutoff
No  public data relating MIC to outcome
Rem: EMA, not FDA require to sample isolates during clinical trials
An assumption that needs to be consolidated
It exist a relationship between MIC and clinical outcome or between AST results (S,I,R) and clinical outcomes

60. Conclusions and Clinical Relevance—Recovery of tilmicosin-resistant M haemolytica or P multocida isolates was rare, and no association was detected between MIC of tilmicosin and treatment response

61. MIC vs. clinical cure for sensitive strains (n=160) for a quinolone

62. AST results and clinical outcomes (Merged results for 4 AMDs from 3 different classes)
Percentage
AST
cure
failure
improvement S
(n=364)
72.5
19.5
8.0 I
(n=23)
69.6
21.7
8.7 R
(n=17)
52.9
41.2
5.9
Pulmonary conditions; Pasteurella multocida and Manheimia haemolytica

63. Decision step: The CBP

64. Decision steps VetCAST will follow EUCAST procedures involving
transparency
consensus (not a vote)
Independence
For VetCAST, as currently is the case for EUCAST, the veterinary pharmaceutical industry will be a partner and will have an active consultative role, but will not have a financial role or participate in decision-making.

65. Decision step
There is no generally accepted formula or mechanism for combining these different pieces of information into a single CBP to define the Susceptible category.
Decisions in the final analysis are a matter of judgment by experts drawn from several disciplines and based on reflective consideration of all available information.
in addition any other factors, scientific or non-scientific, that are relevant to practical conditions, to ensure harmonization between EU countries will be also considered

66. Clinical breakpoint vs ECOFF

67. CBP and dosage regimen
Operationally, if the PK/PD breakpoint is below the ECOFF, it probably means that the current dosage regimen for that AMD is too low to treat the wild-type population. In this case, VetCAST will not establish a CBP dividing the wild-type MIC distributions

68. Diameters vs. MICs Diameter is a surrogate of MIC
What is the value of this surrogate?
Convenience
Reliability?
For harmonisation

69. For a quinolone: MIC vs. Diameters
Diameters (mm)
MIC: µg/mL
MIC should be the independent variable when discussing this relationship

70. Expert comments
To assist clinical microbiologists in preparing their report, VetCAST will provide ad hoc guidance documents for interpretation of ASTs. This will ensure the adequate and contextually correct interpretation of AST results in the light of the animal’s local or regional circumstances.

71. Conclusion Position paper
“En route towards European Clinical Breakpoint for veterinary antimicrobial susceptibility testing: the VetCAST approach”