Pharmacotherapeutic group: Otologicals/corticosteroids and anti-infectives in combination.
ATCvet code: QS02CA91
Pharmacodynamic properties
The veterinary medicinal product is a fixed combination of three active substances (corticosteroid, antifungal and antibiotic).
Mometasone furoate is a corticosteroid with high potency. Like other corticosteroids, it has anti-inflammatory and anti-pruritic properties.
Terbinafine hydrochloride is an allylamine with a pronounced fungicidal activity. It selectively inhibits the early synthesis of ergosterol, which is an essential component of the membrane of yeasts and fungi including Malassezia pachydermatis (MIC90 of 1 μg/ml). Terbinafine hydrochloride has a different mode of action to azole antifungals, therefore there is is no cross-resistance with azole antifungals. Decreased in vitro susceptibility to terbinafine has been reported for strains of Malassezia pachydermatis which form biolfilms.
Florfenicol is a bacteriostatic antibiotic which acts by inhibiting protein synthesis, through binding to and acting on the 50S ribosomal subunit of bacteria. Its spectrum of activity includes Gram-positive and Gram-negative bacteria including Staphylococcus pseudintermedius (MIC90 of 2 μg/ml). In vitro activity of florfenicol against Pseudomonas spp. is low (MIC90 >128 μg/ml).
Florfenicol resistance genes detected in staphylococci include cfr and fexA. Cfr modifies the RNA in the drug binding site (causing reduced affinity to chloramphenicol, florfenicol and clindamycin) and the cfr gene can be present in plasmids or other transmissible elements. FexA codes for a membrane associated with efflux system (affecting both florfenicol and chloramphenicol efflux) and is found in chromosomes as well as in plasmids.
Pharmacokinetic particulars
Systemic absorption of the three active substances was determined after single co-administration into one ear canal of healthy beagle dogs. Mean peak plasma concentrations (Cmax) were low with 1.73 ng/ml florfenicol, 0.35 ng/ml mometasone furoate and 7.83 ng/ml terbinafine HCl reached at the tmax of 24 h, 0.5 h and 20 h after treatment, respectively.
The extent of the transcutaneous absorption of topical medications is determined by many factors including the integrity of the epidermal barrier. Inflammation can increase the transcutaneous absorption of the veterinary medicinal products across the skin adjacent to the external opening of the ear canal.