Itraconazole for Horses: Uses, Dosing & Side Effects

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Itraconazole is a prescription triazole antifungal medication used in veterinary medicine to treat certain fungal infections. In horses, it is most often discussed as part of treatment plans for fungal eye disease such as keratomycosis, and it may also be considered for some systemic fungal infections depending on the organism involved, culture results, and how sick the horse is.

This medication is usually used off-label in horses, which is common in equine medicine. That means your vet may prescribe it based on published veterinary references, clinical experience, and the specific infection being treated. Itraconazole works by interfering with fungal cell membrane production, which helps slow or stop fungal growth.

Itraconazole is not a medication pet parents should start on their own. Fungal infections can look similar to bacterial, inflammatory, or traumatic problems, and the wrong treatment can delay recovery. Your vet may recommend fungal culture, cytology, corneal evaluation, or other testing before choosing itraconazole.

In horses, itraconazole is used most commonly as part of a treatment plan for fungal keratitis or keratomycosis, a serious fungal infection of the cornea. Merck notes that itraconazole is used in horses as part of treatment regimens for keratomycosis, and topical itraconazole has been used successfully for fungal corneal ulcers.

Your vet may also consider oral itraconazole for selected systemic mycoses or invasive fungal infections when the suspected organism is likely to respond and when the horse can tolerate oral therapy. These cases are less common than eye infections in horses, and treatment decisions usually depend on fungal species, severity, tissue involved, and whether other antifungals such as fluconazole, voriconazole, or amphotericin B may be a better fit.

Itraconazole is not a routine first choice for every fungal problem. For example, superficial skin fungal disease in horses is often managed with topical therapy rather than systemic antifungals. The best option depends on where the infection is located, how deep it is, and what testing shows.

Itraconazole dosing in horses varies by formulation, infection site, and treatment goal. A commonly cited equine oral dose in veterinary references is 5 mg/kg by mouth every 24 hours or 2.5 mg/kg by mouth every 12 hours. Some references list broader oral antifungal dosing ranges of 5 to 10 mg/kg by mouth every 24 hours for itraconazole-class use, but your vet will tailor the plan to the horse, the fungal organism, and response to treatment.

For eye infections, dosing is very different. Topical itraconazole is usually a compounded ophthalmic medication and may need to be given very frequently, especially early in treatment. Horses with severe fungal corneal ulcers often need intensive therapy, sometimes through a subpalpebral lavage system so medication can be delivered safely and consistently.

Itraconazole absorption can be affected by formulation and feeding status, so do not switch between capsules, liquid, or compounded products unless your vet tells you to. Treatment often lasts weeks to months, especially for deep or stubborn fungal infections. If you miss a dose, contact your vet or follow the label instructions rather than doubling the next dose.

Many horses tolerate itraconazole reasonably well, but side effects can happen. The most common concerns with oral azole antifungals are digestive upset, including reduced appetite, loose manure, or general gastrointestinal discomfort. Because fungal infections often require long treatment courses, even mild side effects are worth reporting to your vet early.

Itraconazole and other azole antifungals can also affect the liver, so your vet may recommend baseline and follow-up bloodwork during treatment, especially if therapy is prolonged or your horse already has liver concerns. Watch for decreased appetite, lethargy, jaundice, or worsening performance, and call your vet if you notice these changes.

A less common but important caution is that itraconazole has a negative inotropic effect in humans, meaning it can weaken heart contraction. That does not mean every horse will have a heart problem on this drug, but it is one reason your vet may be more cautious in horses with known cardiac disease, poor perfusion, or multiple medications. With topical eye use, local irritation, tearing, or discomfort may occur, but the underlying eye infection itself is often the bigger source of pain.

Itraconazole has the potential for meaningful drug interactions because azole antifungals can affect how other medications are metabolized. This matters most with oral treatment. Tell your vet about every medication, supplement, ulcer treatment, and compounded product your horse receives, including over-the-counter items.

Medications that change stomach acidity may alter absorption of some itraconazole formulations. That means ulcer medications or acid-suppressing drugs may affect how well the drug is absorbed. Your vet may adjust timing, choose a different formulation, or select another antifungal if absorption is a concern.

Itraconazole may also interact with drugs that have their own liver or heart effects, or with medications metabolized through similar enzyme pathways. In horses receiving multiple systemic drugs, your vet may recommend extra monitoring, dose adjustments, or a different antifungal plan. For topical ophthalmic itraconazole, documented systemic interactions are much less of a concern, but your vet still needs the full medication list.