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Pharmacological particulars
Pharmacotherapeutic group: Otologicals, corticosteroids and anti-infectives in combination ATCvet code: QS02CA01
Pharmacodynamic properties
Miconazole belongs to the group of N-substituted imidazole derivatives and inhibits ergosterol de novo synthesis. Ergosterol is an essential membrane lipid and must be synthesised by fungi. Ergosterol deficiency impedes numerous membrane functions, eventually leading to the cell’s death. The spectrum of activities covers nearly all fungi and yeasts of relevance to veterinary medicine as well as Gram-positive bacteria. Practically no development of resistance has been reported. Miconazole has a fungistatic mode of action, but high concentrations are also observed to produce fungicidal effects.
Polymyxin B belongs to the polypeptide antibiotics which are isolated from bacteria. It is only active against Gram-negative bacteria. The development of resistance is chromosomal in nature and the development of resistant Gram-negative pathogens is a relatively rare event. However, all Proteus species share a natural resistance to polymyxin B.
Polymyxin B binds to phospholipids in the cytoplasmic membrane to disturb membrane permeability. This results in autolysis of the bacteria, thus achieving bactericidal activity.
Prednisolone is a synthetic corticosteroid and is used for its anti-inflammatory, anti-pruritic, anti- exudative and anti-proliferative effects. The anti-inflammatory activity of prednisolone acetate results from reduction of the permeability of capillaries, improved blood flow and inhibition of fibroblast action.
The exact mechanism of the acaricidal effect is unclear. It is assumed that the mites are suffocated or immobilised by the oily excipients.
Pharmacokinetic particulars
Following topical application of polymyxin B, there is virtually no absorption of the compound through intact skin and mucous membranes, but significant absorption via wounds.
After topical application of miconazole, there is virtually no absorption of the compound through intact skin or mucous membranes.
When applied topically to intact skin, prednisolone is subject to limited and delayed absorption. Greater absorption of prednisolone should be expected in cases of compromised skin barrier function (e.g. skin lesions).