⚠️ Research Use Only. Not validated for clinical diagnostic use.

Antibiotic Synergy (FIC) Calculator

Checkerboard assay FIC index calculation. Determine if two antibiotics are synergistic, additive, indifferent, or antagonistic.

Checkerboard FIC Calculation

Enter the MIC of each drug alone and in combination. FIC-A = MIC-A(combo) / MIC-A(alone).

Drug A name

Drug B name

MIC of A alone (µg/mL)

MIC of B alone (µg/mL)

MIC of A in combo (µg/mL)

MIC of B in combo (µg/mL)

FIC-A

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FIC-B

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FIC Index

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Interpretation

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What is the FIC index?

Fractional Inhibitory Concentration index = FIC-A + FIC-B, where FIC-A = MIC of drug A in combination / MIC of drug A alone.

How to interpret FIC index?

≤0.5 Synergistic, >0.5–1 Additive, >1–2 Indifferent, >2 Antagonistic.

What is a checkerboard assay?

A method to test antibiotic synergy where two drugs are combined in a 2D dilution matrix and the MIC of each in combination is determined.