Fusidic acid is an antibiotic that belongs to a group of its own, the fusidanes. The molecule has a steroid-like structure but does not possess any steroid activity. The structure is thought to be responsible for the steroid-like high penetration, and for the fact that no cross-resistance or crossallergy has been seen with other antibiotics in routine clinical use. The anti-microbial activity of fusidic acid is specifically aimed at the most common skin pathogens, including Staphylococcus aureus, towards which it is one of the most potent antibiotics. The place of fusidic acid in dermatology is in the treatment of mild to moderately severe skin and soft-tissue infections, e.g. impetigo, folicullitis, erythrasma, furunculosis, abscesses and infected traumatic wounds, whereas it is of less use in conditions such as hidradenitis suppurativa, chronic leg ulcers, burns and pressure sores. The topical combinations of fusidic acid with either betamethasone or hydrocortisone are extremely useful in the treatment of atopic dermatitis/eczema whenever staphylococcal/secondary infection is suspected, and in more persistent cases of eczema where staphylococcal superantigen may be playing an important exacerbating role.
Most of the issues concerned with the role of Staphylococcus aureus and skin bacteria as a cause or as an aggravating factor in eczema have already been considered in earlier reports, as has the choice of antibiotic and the role of bacterial resistance and of S. aureus as superantigen. This paper concentrates on the key criteria with respect to choice and use of antibiotics in superficial skin infections and in infected eczema, with focus on fusidic acid. In essence, this relates to effectiveness (especially against S. aureus), differential bacterial resistance, tolerance (especially potential for allergic contact dermatitis) and comparative cost/cost effectiveness.