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Fluconazole Side Effects in Dogs

Fluconazole for Dogs

Fluconazole side effects in dogs are something to be aware of when dogs are first put on the medication. Fluconazole is a medication that is often used to treat yeast or fungal infections in people. This drug is available both as as generic (fluconazole) and brand-name drug. The brand name of fluconazole is Diflucan. Although a medication designed for humans, fluconazole is often used in dogs for fungal conditions such as fungal skin infections, fungal toenail infections or systemic fungal diseases such as Valley Fever (coccidiomycosis), which my spread to bones, lungs and the central nervous system.

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Fluconazole For Dogs

Fluconazole is a first-generation triazole antifungal medication. It belongs to a class of drugs often referred to as "azole antifungals." This drug was patented for human use in 1981 and then came into commercial use in 1988. While this drug is not aproved for use in dogs by the Food and Drug Administration, it can be legally prescribed by veterinarians as an extra-label drug.

Fluconazole works by causing interference to the cell membranes of fungi and yeasts. This drug basically causes holes in the cell membranes, which leads to essential constituents of the cells to leak out. Overtime, this stops the growth of fungi or yeast, which helps clear up the infection.

Fluconazole, in order to be effective, must be kept at a constant level. This means it helps to give this drug at the same time each day. Generally, fluconazole takes 10 days to 2 weeks to evoke a clinical response. This drug should never be stopped too early even if the symptoms disappear after a few days. Stopping fluconazole early may cause a relapse and return of the infection.

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Compared to ketoconazole, another popular azole antifungal medication, fluconazole has been found to be more effective in crossing the blood-brain barrier, therefore making it the drug of choice for treating certain fungal conditions. Compared to other antifungals such as miconazole, itraconazole and ketoconazole, fluconazole is also less likely to cause side effects; however, it tends to be mre expensive.

Fluconazole Side Effects in Dogs

Fluconazole side effects in dogs

Fluconazole side effects in dogs

Fluconazole is generally well tolerated by dogs, but in some cases dogs may develop adverse reactions. Veterinarians who prescribe fluconazole do so because they have judged that the benefits outweigh the risks for side effects. Certain medical conditions such as systemic fungal diseases like coccidiomycosis often require prolonged treatment with fluconazole (2 to 4 months). Sometimes treatment may be even lasting as long as 8 months to one year.

Problems With the Gastro-intestinal Tract

The most common side effects of fluconazole affect the dog's gastro-intestinal tract. Dogs may develop loss of appetite, nausea, vomiting and diarrhea. Often giving fluconazole with food can help overcome some of these digestive problems.

Liver Problems

Allergic Reactions 

Fluconazole should be avoided in dogs with liver problems as this drug can be quite hard on the dog's liver and there are risks that it may lead to liver disease and liver failure in some cases (hepatotoxicity of the liver).

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Typically, a fungal disease such as Valley Fever very rarely affect the dog's liver and therefore liver issues would most likely be due to the use of this medication, explains veterinarian Dr. Joey.

It may prove to be beneficial putting dogs who are taking fluconazole on a supplement that may help protect the liver such as Denamarin (SAMe and silybin from milk thistle) or Denosyl (SAMe). Both these products are supplements sold over the counter which have good anti-oxidant properties that help protect against liver damage and enable the liver to function properly.

Vets will ask that owners of dogs puts on high doses or long-term dosages of fluconazole bring their dogs in for routine blood tests so to monitor liver function. Increases in ALT in the bloodwork are a possible sign of potential liver failure when presented along with decreased appetite.

Owners of dogs on fluconazole should report to the vet should their dogs show symptoms of liver problems such as itching, yellowing of the skin or whites of the eyes (jaundice), loss of appetite, nausea, vomiting and abdominal pains.

"Hepatotoxicity is possible and approximately 15-20% of dogs treated long-term may have increased ALT (a liver enzyme) concentrations. "~Dr. Michael Salkin, veterinarian

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Kidney Problems 

While the liver is the main organ responsible for detoxifying drugs, the kidneys are the main organs responsible for excreting drugs. It is estimated that 90 percent of the elimination of fluconazole occurs through the dog's kidneys.

Because fluconazole is excreted by the dog's kidneys, the dose should be reduced in dogs with impaired kidney function. Increasing the dosage interval may be something also suggested so to reduce the chances for side effects. Fluconazole should be safe to use in old dogs as long as they have normal liver and kidney function. This should have been determined through bloodwork and urine tests prior to the initial administration of the drug.

"Renal excretion accounts for > 90% of the elimination of fluconazole. It diffuses into saliva, body fluids, and CSF. The dosage interval must be increased in patients with renal failure. "~Dr. Jane Sykes

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Any drug has the potental to cause allergic reactions to dogs. Allergic reactions to drugs are considered immune-mediated responses. It's important therefore to recognize signs of a possible allergic reaction to this drug.

Dog owners should watch for presence of hives, difficulty breathing; swelling of the dog's face, lips, tongue, or throat, vomiting and diarrhea. If you notice any of these signs, report to a veterinarian immediately. Your vet may need to provide a shot of epinephrine given intramuscularly. Left untreated, allergic reactions may lead to severe respiratory compromise, low blood pressure and collapse.

Mild, non-life-threatening cases of allergic reactions may benefit from antihistamines so to reduce minor signs such as urticaria (hives) and itching. Glucocorticoids instead, may help down-regulate pro-inflammatory mediators several hours after the acute event, explains Dr. Jennifer L. Garcia, a board-certified veterainarian specializing in internal medicine.

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  • DVM360: Recognizing and treating adverse drug reactions (Proceedings) May 01, 2011
  • DVM360: Journal Scan: Anaphylaxis in dogs and cats: Are you prepared?
  • DVM360: Frustrating fungal diseases (Proceedings)

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