Fusidic acid, sold under the brand name Fucidin among others, is a steroid antibiotic that is often used topically in creams or ointments and eyedrops but may also be given systemically as tablets or injections.

[medical citation needed] Fusidic acid has no known useful activity against enterococci or most Gram-negative bacteria (except Neisseria, Moraxella, Legionella pneumophila, and Bacteroides fragilis).

[4] Although many strains of MRSA remain sensitive to fusidic acid, there is a low genetic barrier to drug resistance (a single point mutation is all that is required), fusidic acid should never be used on its own to treat serious MRSA infection and should be combined with another antimicrobial such as rifampicin when administering oral or topical dosing regimens approved in Europe, Canada, and elsewhere.

[5] Fucidin tablets and suspension, whose active ingredient is sodium fusidate, occasionally cause liver damage, which can produce jaundice (yellowing of the skin and the whites of the eyes).

[10] Fusidic acid acts as a bacterial protein synthesis inhibitor by preventing the turnover of elongation factor G (EF-G) from the ribosome.

[16] This interaction prevents the necessary conformational changes for EF-G release from the ribosome, effectively blocking the protein synthesis process.

[22] In vitro susceptibility studies of US strains of several bacterial species such as S. aureus, including MRSA and coagulase negative Staphylococcus, indicate potent activity against these pathogens.

However, at least in Canadian hospitals, data collected between 1999 and 2005 showed rather low rate of resistance of both methicillin-susceptible and methicillin-resistant to fusidic acid, and mupirocin was found to be the more problematic topical antibiotic for the aforementioned conditions.

[33] The product of fusB-type resistance genes is a 213-residue cytoplasmic protein which interacts in a 1:1 ratio with EF-G. FusB-type proteins bind in a region distinct from fusidic acid to induce a conformational change which results in liberation of EF-G from the ribosome, allowing the elongation factor to participate in another round of ribosome translocation.

[36] In August 2011, the UK's Medicines and Healthcare products Regulatory Agency issued a Drug Safety Update warning that "systemic fusidic acid (Fucidin) should not be given with statins because of a risk of serious and potentially fatal rhabdomyolysis.

There is evidence from compassionate use cases that fusidic acid may be effective in the treatment of patients with prosthetic joint-related chronic osteomyelitis.