2. Antimicrobial Susceptibility Tests Measure either MIC or zone diameter Report result as S, I or R Clinical utility depends on predictive value (PV) PV rarely reported in clinical trials Can we make it a reporting standard? If it is poor, can we improve it?

3. Predictive Value of AST PV = T / (T+F) PVs = TS / (TS+FS) = TS / AS PVr = TR / (TR+FR) TR / AR CF S RFRFR TS TR FSFSAS AR ACAF Clinical Response ASTAST

4. 0 50 100 Percent Clinical Success S 909493928991 I 739678839079 R 507765638662 NitFurCefotetCefotax1Cefotax2CipFlox1CipFlox2 Poupard JA, Walsh RA, Kleger B. Antimicrobial Susceptibility Testing. New York: Plenum, 1994; 15-25.

5. Predictive Values of AST 0 10 20 30 40 50 60 70 80 90 100 NitFurCefTetCefTax1CefTax2CipFlx1CipFlx2 PVsPVr

6. Antimicrobial Susceptibility Testing Isolated pathogen - is it likely to be the cause? Site of infection - expected antimicrobial concentration? MIC or zone diameter Immune status of the patient Dose, frequency and route of the drug [Evans ER et al. NEJM 1998 Jan 22; 338:232-8.].]

7. Clinically Useful Report P = a  MIC + b   g/mL + c  IS  g  Dose, Route, Frequency, PK If P = probability of cure with an antibiotic, then Where and IS = immune status

8. Clinically Useful Report Specimen: Urine Isolate: E. coli Antibiotic Penicillin G Sulfadimidine Nitrofurantoin Coamoxiclav Ciprofloxacin P of Success 0.40 0.80 0.90 0.85 0.90

9. 0 50 100 Percent Clinical Success S 909493928991 I 739678839079 R 507765638662 NitFurCefotetanCefotax1Cefotax2CipFlox1CipFlox2 Poupard JA, Walsh LR, Kleger B. Antimicrobial Susceptibility Testing. New York: Plenum Press, 1994; 15-25.

10. 0 50 100 Percent Clinical Success S 909493928991 I 739678839079 R 507765638662 NitFurCefotetanCefotax1Cefotax2CipFlox1CipFlox2 Poupard JA, Walsh LR, Kleger B. Antimicrobial Susceptibility Testing. New York: Plenum Press, 1994; 15-25.

11. Antimicrobial Susceptibility Tests vs. Clinical Response Empyema due to S.  -hemolyticus “susceptible” to penicillin G No response to high doses of penicillin G Aspirated pus contained no penicillin, and also inactivated added penicillin Rapid recovery when treatment changed to doxycycline! [Barnes P, Waterworth PM. BMJ 1977 Apr 16; 1:991-3.]