Table 2.

Characteristics of selected veterinary important antifungals.

Antifungal	Mechanism of action	Indications	Resistance mechanism
Griseofulvin	Interaction of griseofulvin with mitotic spindles leads to cell cycle arrest and finally cell death.	Treatment of dermatophytosis Effective against Microsporum spp., Trichophyton spp., and Epidermophyton	Many are not responsive to griseofulvin due to the intrinsic resistance owing to the absence of energy dependent uptake of the drug is present in many fungus
Azole compounds Imidazole Clotrimazole (can, fel), Miconazole (can, fel) Ketoconazole (can, fel) Triazoles Fluconazole (avi,equ, can, fel) Voriconazole (avi, equ, can, fel)	Impairs the ergosterol synthesis by inhibition of lansosterol C14 demethylase enzyme (CYP51A/Erg11p)	Ketoconazole: Effective against Candida, Malassezia pachydermatis, C. immitis, H. capsulatum, and B. dermatitidis and most dermatophytes Useful in canine blastomycosis, histoplasmosis, cryptococcosis, and coccidioidomycosis Itraconazole and fluconazole are more effective than ketoconazole. Proven efficacy of itraconazole against Aspergillosis and in Malassezia dermatitis gives it an edge over ketoconazole. Voriconazole is also effective against Aspergillus and Fusarium Generally, miconazole used as topical agent (cream or spray) in canine dermatophytosis. Systemic use of clotrimazole is limited because of poor oral absorption. However, topical administration is effective in otitis externa caused by Malassezia pachydermatitis. Clotrimazole is effective in nasal aspergillosis and caniduria in small animals.	Increased biosynthesis of lanosterol C14α-demethylase, mutation at the target site (ERG11), efflux pump mediated drug expulsion and alternate pathways to replace ergosterol with other compounds are the major azole-resistance mechanisms.
Terbinafine (avi, can, fel)	Inhibits ergosterol biosynthesis by interacting squaline epoxidase enzyme	Dermatophytosis, topical forms are useful	Terbinafine resistance is uncommon; however, mutation of squalene epoxidase was recorded to mediate such resistance in clinical isolates of dermatophytes.
Polyene compounds Nystatin Natamycin Amphoterecin B	Binds with ergosterol of the fungal plasma membrane causing leakage of essential nutrients and cell death.	Nystatin as topical agent, oral and intestinal candidiasis Natamycin is useful in keratomycosis, nasal aspergillosis, guttural pouch mycosis and dermatophytosis in horses. Amphoterecin B: Histoplasma capsulatum, Cryptococcus neoformans, Coccidioides immitis, Blastomyces dermatitidis, Candida spp., and various species of Aspergillus.	Mutation in ERG3 gene which is responsible for ergosterol biosynthesis leads to incorporation of other sterols in plasma membrance and polyene fails to act on them.