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 Release 22.0, Sept. 2008
 
The Medical Algorithms Project
Chapter : ch25. Antibiotics, Vaccines & Prophylaxis Section : Interpretation of Antibiotic Susceptibility Testing
  Fractional Inhibitory Concentration (FIC)

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Overview :

The fractional inhibitory concentration is an interaction coefficient indicating whether the combined inhibitory/bacteriostatic effect of drugs is synergistic, additive or antagonistic.

 

fractional inhibitory concentration = A + B

 

where:

• A = (MIC of combination X + Y) / (MIC of drug X alone)

• B = (MIC of combination X + Y) / (MIC of drug Y alone)

 

Interpretation:

• synergistic: FIC <= 0.5

• additive: FIC = 1

• antagonistic: FIC >= 4

 

  References:

Jacobs D, Demott W, et al. Laboratory Test Handbook, 3rd edition. Lexi-Comp Inc. Hudson, Ohio. 1994. page 869

Jacobs D, Demott W, et al. Laboratory Test Handbook, 4th edition. Lexi-Comp Inc. Hudson, Ohio. 1996. page 449-450.

Koneman E, et al. Color Atlas and Textbook of Diagnostic Microbiology, 4th edition. J.B. Lippincott Company, 1992. page 652

 

 
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