Fusidic acid, sold under the brand names Fucidin among others, is an antibiotic that is often used topically in creams and eyedrops but may also be given systemically as tablets or injections. The global problem of advancing antimicrobial resistance has led to a renewed interest in its use recently. Pharmacology Fusidic acid acts as a bacterial protein synthesis inhibitor by preventing the turnover of elongation factor G (EF-G) from the ribosome. Fusidic acid is effective primarily on Gram-positive bacteria such as Staphylococcus species, Streptococcus species, and Corynebacterium species. Fusidic acid inhibits bacterial translation and does not kill the bacteria, and is therefore termed "bacteriostatic". Fusidic acid is an antibiotic, derived from the fungus Fusidium coccineum and was developed by Leo Pharma in Ballerup, Denmark and released for clinical use in the 1960s. It has also been isolated from Mucor ramannianus and Isaria kogana. The drug is licensed for use as its sodium salt sodium fusidate, and it is approved for use under prescription in South Korea, Japan, Canada, the EU, Australia, New Zealand, Colombia, Thailand, India and Taiwan. A different oral dosing regimen, based on the compound's pharmacokinetic/pharmacodynamic (PK-PD) profile is in clinical development in the U.S. as Taksta. Mechanism of action Fusidic acid binds to EF-G after translocation and GTP (guanosine-5'-triphosphate) hydrolysis. This interaction prevents the necessary conformational changes for EF-G release from the ribosome, effectively blocking the protein synthesis process. Fusidic acid can only bind to EF-G in the ribosome after GTP hydrolysis. Since translocation is a part of elongation and ribosome recycling, fusidic acid can block either or both steps of protein synthesis. Uses Fusidic acid is active in vitro against Staphylococcus aureus, most coagulase-positive staphylococci, Beta-hemolytic streptococci, Corynebacterium species, and most clostridium species. Fusidic acid has no known useful activity against enterococci or most Gram-negative bacteria (except Neisseria, Moraxella, Legionella pneumophila, and Bacteroides fragilis). Fusidic acid is active in vitro and clinically against Mycobacterium leprae but has only marginal activity against Mycobacterium tuberculosis. One important clinical use of fusidic acid is its activity against methicillin-resistant Staphylococcus aureus (MRSA). 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