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Chapter 23 : Fusidic acid
The steroidal antibiotics are divided into four classes: fusidic acid and its derivatives, helvolic acid and its derivatives, cephalosporin P1 and its derivatives, and viridomic acids A, B, and C. In the various series produced, the most active derivative is 3a-azido-3-deoxyfusidic acid, which has activity equal to 30% of that of fusidic acid. The 7a-hydroxyfusidic derivative has weak antistaphylococcal activity (10% of that of fusidic acid) but is twice as active against streptococci. Fusidic acid inhibits protein synthesis at the translation stage. When fusidic acid is used in combination with other antibacterials, the time to appearance of mutant strains is longer. Researchers in 1986 showed that fusidic acid inhibits the growth of Giardia lamblia in vitro. In patients with hepatic impairment, administration of fusidic acid must be avoided because of the possibility of (reversible) jaundice. It has recently been shown that the pharmacokinetics of fusidic acid in certain patients with hepatic insufficiency are unchanged. Fusidic acid concentrations of 1.0 to 2.3 µg/ml were detected in peritoneal fluid from six of the seven CAPD patients. Fusidic acid is highly albumin bound, on the order of 97 to 98%. Fusidic acid acts on mononuclear cells by reversibly reducing the amounts of interleukin 1 (IL-1) and tumor necrosis factor alpha (TNF-α) released by activated cells. Fusidic acid also prevents the inhibitory effect of IL-β and the stimulatory effect of IL-6 on glucose-induced insulin production in vitro. Fusidic acid is antistaphylococcal antibiotic that does not exhibit cross-resistance with the β-lactams or rifampin.