Presented by Ms. Hindler at the 40th Annual Symposium "Diagnostic and Clinical Challenges of 20th Century Microbes", held on Nov 18, 2010 in Philadelphia.

1. Coping with Updated CLSI Antimicrobial Susceptibility Testing (AST) Challenges Janet A. Hindler, MCLS MT(ASCP) Sr. Specialist, Clinical Microbiology UCLA Medical Center [email_address] “ and a consultant with the Association of Public Health Laboratories”

5. Ceftriaxone Prescribing Information - FDA Breakpoints http://media.pfizer.com/files/products/uspi_ceftriaxone.pdf

12. www.eucast.org

14. www.eucast.org MEROPENEM MIC distribution example Blue = wild type isolates Red = isolates w/ acquired “R” mechanism

16. PK/PD Goal (“Target”) for β -lactams = % of time during dosing interval that drug level in the patient exceeds MIC (%T > MIC) (hypothetical) Serum Concentration (µg/ml) Time (hours) MIC Time above MIC dose dose Cmax (peak concentration)

21. Probability of Target Attainment Imipenem 1g every 8h 4 2 Percent of patients likely to attain desired target 1 Breakpoints ( µ g/ml): Revised = ≤ 1 Old = ≤ 4 Sakka et al. 2007. AAC. 51:3304. S I R

22. Enterobacteriaceae - Carbapenems Revised… Breakpoints (MIC µ g/ml) Corresponding disk diffusion breakpoints also revised CLSI M100-S20-U CLSI 2010 (Old) CLSI June 2010 (Revised) Agent Susc Int Res Susc Int Res Doripenem - - - ≤ 1 2 ≥ 4 Ertapenem ≤ 2 4 ≥ 8 ≤ 0.25 0.5 ≥ 1 Imipenem ≤ 4 8 ≥ 16 ≤ 1 2 ≥ 4 Meropenem ≤ 4 8 ≥ 16 ≤ 1 2 ≥ 4

23. CLSI M100-S20-U Revised Carbapenem Breakpoints and Dosing Correlates S I R S I R

25. Imipenem Probability of Target Attainment 2 4 Revised Breakpoints ( µ g/ml): ≤ 1S 2I ≥ 4R 1 2 4 1 Sakka et al. 2007. AAC. 51:3304. S S R I R I

26. Carbapenem MIC - Reporting Strategy 1 Perform MHT if MIC 2-4 µ g/ml and “R” to ≥ 1 3 rd gen cephalosporin 2 MHT not needed for routine patient reporting; may perform for Infection Control but DO NOT change “S” or “I” to “R” 3 Change from CLSI M100-S20 January 2010 Meropenem Breakpoints ( µ g/ml) CLSI M100-S20-U Int Res Res Res 3 Res 3 Res Report if MHT positive Susc Susc 2 Res Res 8 Revised BPs 2 Susc Susc 4 Int Int 8 Old BPs 1 Int Int 2 4 Meropenem MIC ( µ g/ml) Res Report if MHT negative Res Report if MHT not done Revised Old ≥ 4 2 ≤ 1 ≥ 16 8 ≤ 4 Res Int Susc

29. What criteria are used by FDA to determine if commercial AST system results are acceptable?* http://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/ucm080564.htm * must also meet criteria for very major, major and minor errors. >89.9 % Test S, I, and R agree with REF S, I, R Category Agreement (CA) >89.9 % Test MIC within +/- 1 doubling dilution of the REF MIC Essential Agreement (EA) FDA Acceptable Limits Defined as… Criteria

33. S, I, R Test MIC AST (revised breakpoints) S, I, R Reference AST* (revised breakpoints) * Disk diffusion, reference broth or agar dilution MIC, other MIC? Acceptable = ≥ 90% overall categoric agreement No very major errors (false “S”) ≤ 7% combined major (false “R”) and minor errors (I/R or I/S) Verify Revised Breakpoints Determine Categoric Agreement vs JH Suggestion (not CLSI recommendation)

34. Ceftriaxone MIC ( µ g/ml) vs. Zone Diameter (mm) CLSI Previous (MIC ≤ 8; zone ≥21) vs. Revised (MIC ≤ 1; zone ≥23) Breakpoints for Enterobacteriaceae Jones et al. 2005. Diagn Microbiol Infect Dis. 52:235-246. previous Susc Res revised

35. Example: Categoric (S, I, R) Agreement Test MIC Panels vs. Reference Disk Diffusion Old vs. Revised Breakpoints - Ceftriaxone Old Breakpoints: 1 minor error Revised Breakpoints: 1 major errors (false R) 1 minor error Revised Breakpoints (S, I, R) OLD Breakpoints (S, I, R) 5 4 3 2 1 Strain R I S S S ≥ 21, 14-20, ≤ 13 Reference DD 12 19 21 23 25 Ref DD (mm) ≥ 23, 20-22, ≤ 19 ≤ 1, 2, ≥ 4 ≤ 8, 16-32, ≥ 64 R R I S S Reference DD R R R R S Test MIC 32 8 4 4 1 Test MIC ( µ g/ml) R S S S S Test MIC

37. www.clsi.org

38. Thank you!