TABLE 3.
Minimal fractional inhibitory concentration (FIC) summations for pairwise and triple antimicrobial combinations
| Drug combination | FIC sum | Interpretation |
|---|---|---|
| Rifampin + azithromycina | 0.47 | Synergy |
| Minocycline + azithromycina | 0.43 | Synergy |
| Rifampin + minocyclinea | 0.41 | Synergy |
| Chloramphenicol + azithromycin | 0.53 | No interaction |
| Chloramphenicol + rifampina | 0.60 | No interaction |
| Chloramphenicol + minocycline | 0.75 | No interaction |
| Florfenicol + rifampina | 0.68 | No interaction |
| Levofloxacin + minocyclinea | 0.95 | No interaction |
| Levofloxacin + azithromycina | 1.6 | No interaction |
| Levofloxacin + rifampina | 1.36 | No interaction |
| Levofloxacin + chloramphenicol | 2.0 | No interaction |
| Ceftriaxone + azithromycina,b | 0.49 | Synergy |
| Ceftriaxone + levofloxacina,b | 0.88 | No interaction |
| Azithromycin + rifampin + minocycline | 0.325 | Synergy |
| Axis planesc | ||
| Azithromycin × minocycline | 0.383 | |
| Azithromycin × rifampin | 0.375 | |
| Minocycline × rifampin | 0.375 |
a
FIC data are based on finer √2-fold serial dilution rather on than standard doubling dilution matrices.
b
FIC data for ceftriaxone combinations shown are for axenic rather than intracellular growth inhibition. Ceftriaxone did not sufficiently suppress intracellular growth at all concentrations tested, thus precluding intracellular FIC analysis.
c
FIC values for the axis planes are calculated from within the three-dimensional data set. Two-dimensional synergy FIC values for the same antimicrobial combinations shown earlier in the table are from separate experiments.