THE MERCK VETERINARY MANUAL
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Topical Antifungal Agents

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A number of agents that have antifungal activity are applied topically, either on the skin, in the ear or eye, or on mucous membranes (buccal, nasal, vaginal) to control superficial mycotic infections. Concurrent systemic therapy with griseofulvin is often helpful for therapeutic management of dermatophyte infections. The hair should be clipped from affected areas and the nails trimmed to fully expose the lesions before antifungal preparations are applied. Bathing the animal may also be helpful. Isolation or restricted movement of infected animals is wise, especially when dealing with zoonotic fungi.

Preparations may be used in the form of solutions, lotions, sprays, powders, creams, or ointments for dermal application, or in the form of irrigant solutions, ointments, tablets, or suppositories for intravaginal use. The concentration of active principle in these preparations varies and depends on the activity of the specific agent.

The clinical response to local antifungal agents is unpredictable. Resistance to many of the available drugs is common. Spread of infection and reinfection add to the difficulty of controlling superficial infections. Perseverance is often an essential element of therapy.

Some topical antifungal agents that have been used with success in various conditions and species include iodine preparations (tincture of iodine, potassium iodide, iodophors), copper preparations (copper sulfate, copper naphthenate, cuprimyxin), sulfur preparations (monosulfiram, benzoyl disulfide), phenols (phenol, thymol), fatty acids and salts (propionates, undecylenates), organic acids (benzoic acid, salicylic acids), dyes (crystal [gentian] violet, carbolfuchsin), hydroxyquinolines (iodochlorhydroxyquin), nitrofurans (nitrofuroxine, nitrofurfurylmethyl ether), imidazoles (miconazole, ticonazole, clotrimazole, econazole, thiabendazole), polyene antibiotics (amphotericin B, nystatin, pimaricin, candicidin, hachimycin), allylamines (naftifene, terbinafine), thiocarbamates (tolnaftate), and miscellaneous agents (acrisorcin, haloprogin, ciclopirox, olamine, dichlorophen, hexetidine, chlorphenesin, tiacetin, polynoxylin, amorolfine).

Amorolfine is a topical antifungal agent used to treat onychomycosis and dermatophytosis. It is prepared as a cream or nail lacquer. Amorolfine is a morpholine derivative that appears to interfere with the synthesis of sterols essential for the functioning of fungal cell membranes. In vitro, activity has been shown against some yeasts and dimorphic, dematiaceous, and filamentous fungi (Blastomyces dermatitidis, Candida spp, Histoplasma capsulatum, Sporothrix schenckii, and Aspergillus spp). Despite its in vitro activity, amorolfine is inactive when given systemically and thus is limited to topical use in the treatment of superficial infections. Its role in the treatment of fungal infection in animals is not clear.

Terbinafine is an allylamine antifungal agent available as a topical cream or as tablets. It decreases synthesis of ergosterol by inhibiting squalene epoxidase and is used in the treatment of dermatophytes (eg, Trichophyton, Microsporum, and Aspergillus spp). Terbinafine is also active against yeasts (eg, Blastomyces dermatitidis, Cryptococcus neoformans, Sporothrix schenckii, Histoplasma capsulatum, Candida, and Pityrosporum spp). Terbinafine increasingly is used in combination with other antifungal drugs to enhance efficacy.

Last full review/revision March 2012 by Dawn Merton Boothe, DVM, PhD, DACVIM, DACVCP

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