Abstract
BackgroundStaphylococcal infection of the canine epidermis and hair follicle is amongst the commonest reasons for antimicrobial prescribing in small animal veterinary practice. Topical therapy with fusidic acid (FA) is an attractive alternative to systemic therapy based on low minimum inhibitory concentrations (MICs, commonly <0.03 mg/l) documented in canine pathogenic staphylococci, including strains of MRSA and MRSP (methicillin-resistant Staphylococcus aureus and S. pseudintermedius). However, permeation of canine skin by FA has not been evaluated in detail. This study aimed to define the degree and extent of FA permeation in canine skin in vitro from two sites with different hair follicle density following application of a licensed ophthalmic formulation that shares the same vehicle as an FA-betamethasone combination product approved for dermal application in dogs. Topical FA application was modelled using skin held in Franz-type diffusion cells. Concentrations of FA in surface swabs, receptor fluid, and transverse skin sections of defined anatomical depth were determined using high-performance liquid chromatography and ultraviolet (HPLC-UV) analysis.ResultsThe majority of FA was recovered by surface swabs after 24 h, as expected (mean ± SEM: 76.0 ± 17.0%). FA was detected within 424/470 (90%) groups of serial sections of transversely cryotomed skin containing follicular infundibula, but never in 48/48 (100%) groups of sections containing only deeper follicular structures, nor in receptor fluid, suggesting that FA does not permeate beyond the infundibulum. The FA concentration (mean ± SEM) in the most superficial 240 μm of skin was 2000 ± 815 μg/g.ConclusionsTopically applied FA can greatly exceed MICs for canine pathogenic staphylococci at the most common sites of infection. Topical FA therapy should now be evaluated using available formulations in vivo as an alternative to systemic therapy for canine superficial bacterial folliculitis.
Highlights
Staphylococcal infection of the canine epidermis and hair follicle is amongst the commonest reasons for antimicrobial prescribing in small animal veterinary practice
fusidic acid (FA) recovery The amount of FA applied to canine skin in each diffusion cell ranged from 762 to 1087 μg
Further studies that optimise parameters, such as applicator pressures, numbers of repeat strips and clipping methods [20] for the thin but compact corneal layers of canine haired skin, are indicated. These data suggest that topical FA should be useful in the treatment of canine surface and superficial pyoderma caused by bacteria susceptible to fusidic acid, in countries where it is available, but not deep pyoderma
Summary
Staphylococcal infection of the canine epidermis and hair follicle is amongst the commonest reasons for antimicrobial prescribing in small animal veterinary practice. In canine practice, surface infections (confined to the interfollicular epidermis) are treated topically, whereas superficial infections such as bacterial folliculitis (that extend to the follicular infundibulum without extension into the Fusidic acid (FA) is an antibiotic which has a steroidlike structure, with proven activity in vitro against coagulase-positive staphylococci including MRSP [6, 7]. Frosini et al BMC Veterinary Research (2017) 13:345 living epidermis, after topical application [8, 9] These features correlate with clinical efficacy of licensed FAcontaining topical veterinary products in surface infections such as canine acute moist [pyotraumatic] dermatitis [10]. Studies of clinical efficacy of topical FA in canine superficial pyoderma / bacterial folliculitis are lacking [4, 11]
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