Pharmacology: Pharmacodynamics: Fusidic acid is a steroidal antibacterial with a bacteriostatic or bactericidal activity, mainly against Gram-positive bacteria. Fusidic acid inhibits bacterial protein synthesis although, in contrast to drugs such as macrolides or tetracyclines, it does not bind to the bacterial ribosome, but inhibits a factor necessary for translocation of peptide subunits and elongation of the peptide chain. It is capable of inhibiting protein synthesis in mammalian cells but exerts a selective action against susceptible infecting organisms because of poor penetration into the host cell. Fusidic acid is very active against staphylococci, notably Staph. aureus and Staph. epidermidis (including meticillin-resistant strains). Nocardia asteroides and many clostridial strains are also highly susceptible. The streptococci and enterococci are less susceptible. Most Gram-negative bacteria are intrinsically resistant but fusidic acid is active against Neisseria spp. and Bacteroides fragilis. It has some activity against strains of Mycobacterium tuberculosis and is highly active against M. leprae.
Pharmacokinetics: Fusidate is widely distributed into tissues and body fluids, including bone, pus and synovial fluid. It penetrates cerebral abscesses but does not enter CSF in appreciable amounts. It has been found in the fetal circulation and in breast milk. About 95% or more of fusidate in the circulation is bound to plasma proteins. Fusidate has a plasma half-life of about 10 to 15 hours. It is excreted in the bile, almost entirely as metabolites, some of which have weak antimicrobial activity. About 2% appears unchanged in the faeces. Little is excreted in the urine or removed by haemodialysis.