Second Line Drugs Susceptibility Testing: Study Progress Report
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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

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Second Line Drugs Susceptibility Testing: Study Progress Report

Alex Sloutsky

Massachusetts State TB Laboratory

Paris, 2005


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

  • 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

  • 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

Total time allotted per week is 14 hours


WORKLOAD AND WORKFLOW: BACTEC

Total time allotted per week for BACTEC is 46 hours


BUDGET


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


DATABASE


Preliminary Data Analysis


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