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Further information
Pharmacodynamic properties
The veterinary medicinal product is a fixed combination of three active substances (corticosteroid, antifungal and antibiotic):
Hydrocortisone aceponate belongs to the diester class of the glucocorticosteroids with a potent intrinsic glucocorticoid activity which means a relief of both inflammation and pruritus leading to an improvement of clinical signs observed in otitis externa. Miconazole nitrate is a synthetic imidazole derivative with a pronounced antifungal activity.
Miconazole selectively inhibits the synthesis of ergosterol, which is an essential component of the membrane of yeasts and fungi including Malassezia pachydermatis. Mechanisms of resistance to azoles consist of either failure in antifungal accumulation or modification of target enzyme. No standardised in-vitro susceptibility breakpoints have been defined for miconazole; however, using the method by Diagnostics Pasteur, no resistant strains were found.
Gentamicin sulphate is an aminoglycoside bactericidal antibiotic which acts by inhibiting protein synthesis. Its spectrum of activity includes Gram-positive and Gram-negative bacteria, such as the following pathogenic organisms isolated from the ears of dogs: Staphylococcus intermedius, Pseudomonas aeruginosa, Proteus mirabilis, Escherichia coli, etc.
Since many bacterial strains may be involved in otitis externa in dogs, the mechanisms of resistance can vary. The bacterial resistance phenotypes to gentamicin are mainly based on three mechanisms: enzymatic modification of aminoglycosides, failure of intracellular penetration of the active substance and alteration of the aminoglycoside target. Cross-resistance is mainly linked with efflux pumps which confer resistance to β-lactams, quinolones and tetracyclines depending on the specificity of the pump with its substrate. Co-resistance has been described, i.e. gentamicin resistance genes are found to be physically linked to other antimicrobial resistance genes that are transferred between pathogens due to transferable genetic elements such as plasmids, integrons and transposons. Gentamicin resistant bacteria isolated from the field between 2008 and 2010 in canine otitis before treatment (determined according to CLSI guideline breakpoint ≥ 8 for all isolates except for Staphylococci ≥ 16 μg/ml) were low: 4.7%, 2.9% and 12.5% for Staphylococcus spp., Pseudomonas and Proteus spp. respectively. All Escherichia coli isolates were fully susceptible to gentamicin.
Pharmacokinetic particulars
After application of the veterinary medicinal product into the ear canal, absorption of miconazole and gentamicin through the skin is negligible.
Hydrocortisone aceponate belongs to the diesters’ class of glucocorticosteroids. The diesters are lipophilic components ensuring an enhanced penetration into the skin associated with low systemic bioavailability. The diesters are transformed inside the skin structures in C17 monoesters responsible for the potency of the therapeutic class. In laboratory animals, hydrocortisone aceponate is eliminated the same way as hydrocortisone (other name for endogenous cortisol) through urine and faeces.