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Fungal Infections are a common cause of disease in both animals and man. Many of the fungi and yeasts that cause disease in the animal population are zoonotic and so owners and vets a like are also at risk of infection. As this group of organisms are eukaryotic cells, trying to combat them becomes are more complex and challenging prospect as they have the ability to be toxic to the animal's own cells. Therfore it is important to understand how this drugs work, their potential side effects and which species they are active against.
Polyene Antifungals
This group of drugs are fungicidal and act by forming bonds to ergosterol. Since ergosterol is an important component of the cytoplasmic membrane of the fungal cell, disruption of the permeability of the membrane results leading to cell death.
The three most commonly used drugs in this group are:
Natamycin
- This is active against many filamentous and dimorphic fungi and against yeasts.
- It is only available in topical form for application to the udder, skin, nose, eye and ear.
Nystatin
- It is effective against Candida, Pityrosporum, Cryptococcus, dermatophytes and some filamentous and dimorphic fungi.
- It is also only available in a topical application form.
Amphotericin B
- This can be used topically and systemically and is the most important drug for systemic mycoses.
- It is broad spectrum and is active against deep mycotic infective agents. Though Aspergillus is quite resistant and 50% of yeast causing bovine mastitis are susceptible.
- It isn't absorbed after oral administration but following intravenous administration it binds to lipoproteins and so is slowly released systemically.
- There is some synergy with flucytosine and rifampin but is antagonistic if given with ketaconazole.
- Care must be used when given to dogs and cats as renal toxicity always follows after its use.