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Antimicrobial Susceptibility Tests

Antimicrobial Susceptibility Tests

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Antimicrobial Susceptibility Tests

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  1. 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?

  2. C F Clinical Response S TS FS AS R FR TR AR A S T AC AF Predictive Value of AST • PV = T / (T+F) • PVs = TS / (TS+FS) = TS / AS • PVr = TR / (TR+FR) TR / AR

  3. 100 Percent Clinical Success 50 0 NitFur Cefotet Cefotax1 Cefotax2 CipFlox1 CipFlox2 90 94 93 92 89 91 S 73 96 78 83 90 79 I 50 77 65 63 86 62 R Poupard JA, Walsh RA, Kleger B. Antimicrobial Susceptibility Testing. New York: Plenum, 1994; 15-25.

  4. Predictive Values of AST PVs PVr 100 90 80 70 60 50 40 30 20 10 0 NitFur CefTet CefTax1 CefTax2 CipFlx1 CipFlx2

  5. 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.].]

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

  7. Antibiotic Penicillin G Sulfadimidine Nitrofurantoin Coamoxiclav Ciprofloxacin P of Success 0.40 0.80 0.90 0.85 0.90 Clinically Useful ReportSpecimen:UrineIsolate: E. coli