No synergy has been demonstrated in vitro in most study between Fusidic acid and Rifampicin or Vancomycin and antagonism of the effect of Ciprofloxacin has been reported.
Interaction with the Penicillins are complex, with either antagonism of the effect of one or both agents, or lack of any effect. However, the combination of an anti-Staphylococcal Penicillin with Fusidic acid may prevent the emergence of Fusidic acid resistance Staphylococcal mutants, and such combination may be clinically effective.