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Second Line Drugs Susceptibility Testing: Study Progress Report Alex Sloutsky

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Second Line Drugs Susceptibility Testing: Study Progress Report Alex Sloutsky Massachusetts State TB Laboratory Paris, 2005. B ACKGROUND: Clinical significance of DST.

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Second Line Drugs Susceptibility Testing: Study Progress Report

Alex Sloutsky

Massachusetts State TB Laboratory

Paris, 2005

b ackground clinical significance of dst
BACKGROUND: Clinical significance of DST
  • It is common among clinicians to assume that if culture is resistant to a particular drug in vitro, this drug will be ineffective in vivo.
  • In reality, prognostic value of pretreatment DST can vary greatly depending on patient-specific factors:

- proportion of resistant bacteria

- whether resistance is acquired or primary

  • Clinical significance of susceptibility testing becomes an issue due to spread of MDR TB.
resiissstaannsensitivity
Resiissstaannsensitivity
  • DST reports list drugs as either “sensitive” or “resistant” which indicates that there are two widely different phenotypes.
  • In reality, resistant strains exhibit a continuum of phenotypes, some of which may be very similar to sensitive, wild-type strains.
  • The task of the laboratory is to classify the level of resistance of a strain of M. tuberculosis in relation to the established “resistance criteria” to a specific drug.
  • These “breakpoints” determine clinically significant level of resistance to a drug, i.e. high enough to affect the efficacy of treatment if the patient is treated with that drug
study design msli lab
Study Design: MSLI Lab
  • Well-defined representative samples of clinical isolates of M. tuberculosis:
    • PR strains have been obtained from patients who failed treatment with the regimens containing the corresponding drug;
    • Probably susceptible (PS) strains: from patients who have never taken anti-TB drugs (unless infected with drug resistant organisms).
  • Source of strains: KIT (Korea), Philippines (TDF), Latvia, Hong Kong, Boston (PIH collection). Total planned:250 strains.
  • MIC to 6 drugs are to be determined: ETH, PAS, KAN, CAP, CYC, OFL by two methods: Agar Plate Proportions and BACTEC.
  • 8 concentrations of each drug used to determine the MIC breakpoint.
workload and workflow agar plate proportions method
WORKLOAD AND WORKFLOW: Agar Plate Proportions Method

Total time allotted per week is 14 hours

workload and workflow bactec
WORKLOAD AND WORKFLOW: BACTEC

Total time allotted per week for BACTEC is 46 hours

projected duration and current status of the project
PROJECTED DURATION AND CURRENT STATUS OF THE PROJECT

Total time per week for 6 strains tested by both methods is 60 hours. It was anticipated that it would take 250/6 = 42 weeks to completion (with no repeat testing and no data analysis).

Personnel hired and trained

Supplies purchased

Forms for recording results created

Up to date: 272 cultures tested by APP method (< 10 to be repeated) and 40 tested by BACTEC. ~230 cultures to go will take ~40 weeks or 10 months

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