Fungal infections, while less common than bacterial or viral ailments, pose significant challenges in veterinary medicine. This guide delves into the various topical and systemic antifungal treatments available for pets and other animals, covering applications in skin, respiratory, aural, and ocular conditions. Understanding these therapies is crucial for veterinarians and pet owners to effectively manage mycotic infections and ensure the well-being of their animal companions.
Topical Antifungal Treatments
Topical antifungal medications are the cornerstone for managing superficial mycotic infections affecting the skin, ears, eyes, and mucous membranes. These preparations, available as solutions, lotions, sprays, powders, creams, or ointments, allow for direct application to the affected areas. Before application, clipping hair from lesions and trimming nails is recommended to ensure full exposure and optimal penetration of the medication. Concurrent systemic treatment, particularly with griseofulvin, can be beneficial for dermatophyte infections. Isolation or restricted movement of infected animals is also advised, especially when zoonotic fungi are involved, to prevent further spread.
The clinical response to topical antifungals can be unpredictable, with resistance to many drugs being a common issue. The spread of infection and reinfection further complicate treatment. Perseverance is therefore a key element in successfully managing these conditions.
A wide array of topical antifungal agents have demonstrated success across various species and conditions. These include:
- Iodine preparations: Tincture of iodine, potassium iodide, and iodophors.
- Copper preparations: Copper sulfate, copper naphthenate, and cuprimyxin.
- Sulfur preparations: Monosulfiram and benzoyl disulfide.
- Phenols: Phenol and thymol.
- Fatty acids and salts: Propionates and undecylenates.
- Organic acids: Benzoic acid and salicylic acids.
- Dyes: Crystal violet and carbolfuchsin.
- Hydroxyquinolines: Iodochlorhydroxyquin.
- Nitrofurans: Nitrofurazone and nitrofurfurylmethyl ether.
- Azoles: Miconazole, tioconazole, clotrimazole, econazole, and thiabendazole.
- Polyene antimicrobials: Amphotericin B, nystatin, pimaricin, candicidin, and hachimycin.
- Allylamines: Naftifine and terbinafine.
- Thiocarbamates: Tolnaftate.
- Miscellaneous agents: Acrisorcin, haloprogin, ciclopirox olamine, dichlorophen, hexetidine, chlorphenesin, triacetin, and polynoxylin.
While less common, mycotic mastitis in cattle can be caused by fungi such as Candida, Cryptococcus, and Trichosporon. Treatment historically involved frequent stripping of the affected quarter, though intra-arterial and intramammary injections of miconazole have also shown successful outcomes.
Respiratory Antifungal Therapies
Systemic antifungals are primarily used in small animals and equine patients to manage fungal pneumonia. However, treating fungal pneumonia in poultry presents significant challenges. Pulmonary aspergillosis is a major cause of morbidity and mortality in avian species, affecting domestic, ornamental, and wild birds. While environmental management and antimycotic disinfectants can help mitigate disease spread, treatment is often unrewarding, and there are no FDA-approved treatments for fungal pneumonia in poultry. Due to the lipophilic nature and long tissue half-life of many antifungal drugs, extended egg and meat withdrawal times must be anticipated for any extra-label use in poultry.
Direct administration of antifungals to the avian respiratory tract is becoming more prevalent. Nebulization or intratracheal administration of amphotericin B, clotrimazole, or miconazole has been described for treating poultry aspergillosis, often in conjunction with systemic treatments like itraconazole.
Instilling antifungals directly into the nasal cavity is a common approach for treating fungal rhinitis in dogs, cats, and horses. Nasal aspergillosis is most frequent in dogs, while C. neoformans primarily affects cats. Other nasal pathogens in dogs and cats include Trichosporon, Blastomyces, and Histoplasma. Nasal aspergillosis has also been reported in horses, with guttural pouch mycosis often caused by Aspergillus spp.
| Drug | Dose, Route, Frequency, Species |
|---|---|
| Amphotericin B | Nebulization: 1 mg/mL in sterile water or saline for 15 minutes, q 6–12 h (avian). Intratracheal: 1 mg/kg, q 8–12 h (avian). |
| Clotrimazole | Nebulization: 1% aqueous solution for 30 minutes, q 24 h (avian). Intratracheal or direct air sac administration: 10 mg/kg (avian). Intranasal: Instill into nasal cavity under general anesthesia for 1 hour, rotating head q 15 min (dogs). |
| Miconazole | 45 minutes/day (avian). Intranasal: 2% miconazole (horses). |
| Enilconazole | Intranasal: 5% solution, instillation under general anesthesia for 1 hour, rotating head q 15 min (dogs). Topical: Instill twice daily via nasal or guttural pouch catheter, q 12 h (horses). |
| Terbinafine | Nebulization: 1 mg/mL in aqueous solution for 20 minutes, q 8 h (avian). |
Aural Antifungal Therapy
Fungal organisms, particularly Aspergillus and yeasts like Malassezia and Candida, can be primary or secondary causes of otitis externa in small animals. Yeast infections are the most common culprits in dogs. While numerous FDA-approved topical products exist for treating otitis externa, severe or refractory cases may necessitate systemic antifungals such as terbinafine, fluconazole, itraconazole, or ketoconazole. Effective topical antifungal products for otitis externa include clotrimazole, miconazole, thiabendazole, acetic acid, and ketoconazole flushes, often in combination with TrizEDTA. Newer single-dose formulations containing terbinafine offer prolonged efficacy for up to 30 days post-administration.
Ocular Antifungal Therapy
Keratomycosis, a fungal infection of the cornea, can be a significant ophthalmic condition in horses, dogs, and cats, with prevalence varying by geographic region. Fungal cultures are recommended to identify the specific fungal species and determine antifungal sensitivity patterns.
Various agents have been successfully used to treat fungal ulcers in horses, including miconazole, natamycin, fluconazole, econazole, voriconazole, clotrimazole, and itraconazole, typically administered topically.
| Drug | Concentration | Frequency | Notes |
|---|---|---|---|
| Fluconazole | 0.2% solution | q 2–6 h | Subconjunctival and intravitreal injections have been described. |
| Itraconazole | 1% ointment/30% DMSO | q 2–6 h | Does not penetrate the anterior chamber. |
| Miconazole | 1% solution | q 2–6 h | Subconjunctival and intracameral injections have also been described. |
| Voriconazole | 1% solution | q 2–6 h | Penetrates intact corneal epithelium. |
| Amphotericin B | 0.075%–5% solution | q 2–6 h | Subconjunctival, intravitreal, and intracameral injections after proper dilution have also been described. |
| Natamycin | 5% suspension | q 2–6 h | Only FDA-approved drug for fungal keratitis (humans); does not penetrate intact corneal epithelium. |
| Terbinafine | 1% ointment | q 2–6 h | Not suitable for deep corneal or intraocular mycoses. |
| Silver Sulfadiazine | 1% ointment/cream | q 6–24 h |
Ophthalmic use of azole antifungals is common, though commercial formulations are not readily available. Compounded miconazole (1% solution) and itraconazole have shown success. Combining itraconazole with 30% dimethyl sulfoxide (DMSO) can enhance corneal drug concentrations, but it does not penetrate the anterior chamber.
Intravenous voriconazole has been used to treat keratomycosis and penetrates the intact cornea, making it a first-line therapeutic choice for equine keratomycosis, especially against susceptible fungi like Fusarium, Aspergillus, and Candida. Systemic voriconazole at 4 mg/kg/day in horses has been reported to achieve concentrations above the AUC:MIC ratio for Aspergillus in the tear film. Topical terbinafine, however, has not resulted in detectable aqueous humor concentrations and is not recommended for deep corneal or intraocular mycosis. Nevertheless, topical terbinafine has shown efficacy in superficial Aspergillus keratomycosis in rabbits.
