Amphotericin B in Dogs

Amphotericin B is a powerful prescription antifungal used in dogs with serious fungal infections. Your vet may consider it when a dog has a life-threatening or widely spread infection such as blastomycosis, histoplasmosis, cryptococcosis, or another deep mycosis. In veterinary medicine, it is usually reserved for cases where a fast, aggressive response is needed or when oral antifungal medication alone may not be enough.

This medication is not a routine at-home drug for most dogs. It is commonly given by intravenous infusion in a hospital setting, and many dogs need repeated treatments plus lab monitoring. Amphotericin B can be very effective, but it also has a narrow safety margin. Kidney injury is the main concern, so your vet will usually pair treatment with careful hydration, bloodwork, urine monitoring, and follow-up planning.

Different formulations matter. Older deoxycholate formulations are still used in some settings, but lipid-based products such as Abelcet and liposomal amphotericin B are often chosen when available because they can reduce kidney exposure and may be better tolerated. None of the amphotericin B formulations are FDA-approved specifically for veterinary use, so use in dogs is generally extra-label under veterinary supervision.

For many dogs, amphotericin B is only one part of the plan. Your vet may combine it with an oral antifungal such as itraconazole or fluconazole, depending on the infection, the organs involved, and your dog’s overall stability. The right plan depends on severity, test results, and what level of care fits your dog and your family.

Amphotericin B works by binding to ergosterol, an important sterol in fungal cell membranes. When it binds there, it disrupts the membrane and creates leaks. That causes loss of key cell contents and can kill or severely damage the fungus. This direct membrane effect is one reason amphotericin B is often used when a dog needs a faster antifungal effect than many oral drugs can provide.

The same mechanism also explains why side effects can happen. While amphotericin B targets fungal cells better than mammalian cells, it can still affect the body, especially the kidneys. Renal blood flow changes and direct tubular injury are major reasons dogs on this medication need close monitoring. That is also why infusion protocols, dilution, and fluid support are such important parts of treatment.

Lipid formulations change how the drug moves through the body. In general, lipid-complex and liposomal products are designed to deliver more drug to infected tissues while reducing exposure to the kidneys. They are often more costly, but they can expand treatment options for dogs at higher risk of kidney complications or dogs needing longer cumulative therapy.

Amphotericin B is usually used for deep or disseminated fungal disease rather than mild surface infections. It may also be used alongside other antifungals in selected cases. Your vet chooses the combination based on the organism involved, the body systems affected, and how urgently fungal burden needs to be reduced.

The most important side effect in dogs is kidney injury. Merck notes that most dogs receiving amphotericin B develop some degree of kidney damage, which is why your vet will usually monitor kidney values, urine, and electrolytes throughout treatment. Risk can increase with dehydration, pre-existing kidney disease, higher cumulative exposure, or use with other medications that also stress the kidneys.

Dogs can also have infusion-related reactions. These may include fever, vomiting, nausea, lethargy, shaking, or general discomfort during or after treatment. Some hospitals premedicate dogs or adjust the infusion rate if reactions occur. Appetite changes and weakness may also be seen, especially in dogs already sick from a systemic fungal infection.

Electrolyte changes are another concern, especially low potassium. Depending on the protocol, your vet may recommend repeat bloodwork before each dose or at least weekly during a treatment series. In some dogs, urine changes can show toxicity earlier than chemistry values, which is why urinalysis may be part of the monitoring plan.

See your vet immediately if your dog becomes very weak, stops eating, vomits repeatedly, drinks or urinates much more than usual, seems dehydrated, or seems worse after an infusion. Those signs do not always mean amphotericin B is the cause, but they do mean your dog needs prompt reassessment.

Amphotericin B dosing in dogs varies by formulation and by your vet’s treatment goal. Merck lists conventional amphotericin B at about 0.25 to 1 mg/kg IV slowly three times weekly, with a total cumulative dose of roughly 4 to 11 mg/kg, or until azotemia develops. Another Merck reference lists deoxycholate protocols around 0.15 to 0.5 mg/kg every 48 hours until a cumulative dose of 4 to 12 mg/kg is reached. Lipid complex products such as Abelcet are listed at 1 to 3 mg/kg IV every other day or three times weekly, while liposomal amphotericin B is listed at 3 to 4 mg/kg IV on similar schedules.

In practice, this is a hospital medication. It is diluted and infused slowly, often over several hours, and many dogs receive IV fluids to lower kidney risk. Your vet may check blood urea nitrogen, creatinine, packed cell volume, total protein, electrolytes, and urinalysis during the course. The exact schedule depends on your dog’s baseline kidney function, hydration status, and how sick they are from the fungal disease itself.

Pet parents should not try to calculate or give this medication at home unless your vet has created a very specific plan and trained you to do so. Most dogs receiving systemic amphotericin B need professional administration. If your dog is also on oral antifungals, continue them exactly as directed and ask your vet what to do if an infusion is delayed or a lab value changes.

Because amphotericin B is often part of a longer fungal treatment plan, your vet may transition your dog to oral medication alone once the dog is more stable. That does not mean the infection is gone. It usually means the treatment strategy is shifting from rapid control to longer-term management.

The biggest practical interaction concern is not one single drug pair. It is the combined effect of amphotericin B with other medications that can stress the kidneys or worsen dehydration. That can include some NSAIDs, certain antibiotics, some chemotherapy drugs, and other nephrotoxic medications. If your dog is on multiple prescriptions, supplements, or recent anesthesia medications, your vet needs the full list before treatment starts.

Electrolyte shifts can also complicate the use of other drugs. If amphotericin B lowers potassium or affects kidney function, medications that depend on normal kidney clearance or stable electrolytes may need adjustment. This is one reason dogs on amphotericin B often have more frequent rechecks than dogs taking oral antifungals alone.

Combination antifungal therapy is sometimes intentional. Merck notes amphotericin B may be combined with flucytosine or minocycline for selected Candida and Cryptococcus cases, and rifampin may potentiate activity against some fungi in certain settings. These are not routine combinations for every dog, and they should only be used when your vet has a clear reason and monitoring plan.

If your dog is receiving amphotericin B ophthalmic rather than systemic IV therapy, the interaction profile is much lighter. VCA notes there are no documented drug interactions for the ophthalmic form, though local irritation can occur. Still, tell your vet about every medication your dog receives, because the eye problem and the rest of your dog’s health still need to be managed together.