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Fusidic acid
General information
Fusidic acid is the best-known representative of a group of antibiotics with steroid structures, which are eliminated primarily by biliary excretion as microbiologically inactive metabolites. The antibacterial action of fusidic acid is bacteriostatic, although it can be bactericidal at higher concentrations. It exerts its antibacterial effect by inhibiting protein synthesis, but the exact mechanism by which this inhibition occurs has not yet been elucidated. It has a narrow antibiotic spectrum, with a bacteriostatic or slow bactericidal effect mainly directed at both coagulase-negative staphylococci and Staphylococcus aureus [ ]. Fusidic acid may also have a role as a clinically useful suppressor of immunoinflammatory processes [ ].
Fusidic acid is adequately absorbed from the gastrointestinal tract, but has also been used topically. It has the important property of good tissue penetration, including entry into bones and joints, but does not reach the cerebrospinal fluid. Elimination of fusidic acid is primarily by non-renal mechanisms, and a proportion is metabolized to several breakdown products detectable in bile. Systemic clearance is increased by hypoalbuminemia, reduced by severe cholestasis, and is unchanged in renal insufficiency [ ].
General adverse effects and adverse reactions
The most common adverse reactions to fusidic acid are minor and are related to the gastrointestinal tract (discomfort, diarrhea) [ ]. Rare adverse effects include granulocytopenia, thrombocytopenia, venous spasm, and skin reactions [ ]. Fusidic acid has detergent properties and can cause hemolysis when injected intravenously or tissue damage when given intramuscularly. However, its systemic toxicity is relatively low.
Bacterial resistance has been an obstacle to the widespread use of fusidic acid; it develops in a single step in vitro and has also been observed in patients, particularly during prolonged administration [ ].
Organs and systems
Hematologic
The hematological adverse effects of fusidic acid, such as granulocytopenia and thrombocytopenia, have been rarely reported. Two cases of fusidic acid-induced leukopenia and thrombocytopenia after 2 weeks of fusidic acid treatment have been reported; in both cases, the abnormality resolved in 3–6 days after withdrawal of fusidic acid [ ].
There have been six reports of fusidic acid-induced sideroblastic anemia after treatment with fusidic acid for 32–190 (mean 81) days; four required repeated blood transfusions [ ]. After fusidic acid withdrawal in five patients, there was complete recovery. In one patient, rechallenge with fusidic acid resulted in recurrence of anemia and resolution resolved after definitive withdrawal.
Gastrointestinal
The major adverse reactions to fusidic acid are mild gastrointestinal discomfort and diarrhea [ ]. Oral fusidic acid can cause Klebsiella oxytoca -associated colitis [ ].
Liver
Fusidic acid is chemically very similar to bile acids and hence competes with them for elimination and metabolism. A patient with a past history of alcohol-induced cirrhosis developed cholestatic jaundice after taking oral fusidic acid for 2 days [ ].
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