Fusidic acid is the only therapeutically useful member of a group of naturally occurring antibiotics that display a steroid-like structure (Figure 1). The antibiotic acts to prevent the translocation step in bacterial protein synthesis by inhibiting one of the substances (factor G) essential for this reaction. Fusidic acid is active in vitro against Gram-positive and Gram-negative cocci, M. tuberculosis, Nocardia asteroides, and many anaerobes; the ribosomes of Gram-negative bacilli are susceptible to the action of the drug, but access is denied by the Gram-negative cell wall.
Figure 1. Chemical structure of fusidic acid
Fusidic acid is usually regarded simply as an antistaphylococcal agent;iIt penetrates well into infected tissues, including bone, and it is used in some countries for the treatment of staphylococcal osteomyelitis. A potential drawback is the presence in the general staphylococcal population of a small number of fusidic acid resistant variants that might proliferate during therapy. For this reason, fusidic acid is usually administered together with another antibiotic, often a penicillin.
Fusidic acid is usually free from side
effects when given orally. Intravenous administration of the diethanolamine salt
is sometimes accompanied by a reversible jaundice. Topical preparations are
available, but their use migth favour the emergence of resistance.
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