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Fluconazole (Diflucan)
Revised: February 01, 2023
Published: October 03, 2005

(For veterinary information only)

The size of the tablet/medication is NOT an indication of a proper dose. Never administer any drug without your veterinarian's input. Serious side effects or death can occur if you use drugs on your pet without your veterinarian's advice. 

It is our policy not to give dosing information over the internet.

Brand Name: Diflucan

Available in 50 mg, 100 mg, 150 mg, 200 mg tablets, and oral suspension


The development of oral medications to be used to treat invasive fungal infections has represented an immense medical breakthrough. With oral treatment available, human patients no longer require hospitalization several days per week for intravenous treatment of their disease; a more normal and productive lifestyle is now possible. Furthermore, the toxicity profiles of the newer oral drugs are improved vs. those of the injectables.

Ketoconazole was the first such oral antifungal drug, but it had room for improvement regarding its side effect potential. There were problems with nausea, liver toxicity, and feminization of male patients. Fluconazole was developed in answer to these concerns. Its potential for side effects is far lower and recently, generic medications have made fluconazole readily affordable. Fluconazole is yet another generation that allows excellent penetration of the blood/brain barrier, permitting neurologic fungal diseases to be treatable, while in the past, they were not.

In short, there are a few reasons for choosing fluconazole over other antifungal agents. One reason is to avoid side effects, especially with long-term use. Fluconazole is not associated with hormone interference and has less trouble with upset stomach reactions. Another reason to choose fluconazole is its ability to penetrate the blood-brain barrier or eye, places where other antifungals cannot go, in order to address a neurologic or ophthalmic infection. Other antifungals are not capable of entering such sequestered areas of the body. Itraconazole is frequently the alternative treatment for systemic fungal disease, and itraconazole is fraught with bioavailability issues and inconvenient dosing sizes. Fluconazole is available as an effective generic and compounding appropriate pet formulae is not difficult.

Itraconazole is fungicidal, meaning it kills the fungus, while fluconazole is fungistatic, which means it prevents the fungus from reproducing. The host's immune system must be strong enough to actually kill the fungus when the patient is on fluconazole.

How this Medication Works

Fluconazole works by inhibiting the fungal enzymes that produce ergosterol, an important component of the fungal cell wall. Without adequate ergosterol, the fungal cell becomes weak, leaky, and ultimately dies.

Fungal infections for which fluconazole can be used include:

Fluconazole is typically given twice daily, with or without food. If a dose is accidentally skipped, the next dose should be given when it is remembered, and the subsequent dose should be timed accordingly.

Side Effects

While fluconazole users do not commonly experience side effects, it is important to know what to watch for.  Side effects of concern are appetite loss, vomiting, and/or diarrhea. If they occur, medication should be discontinued, and liver enzymes should be checked. Despite the overall reduced side effects of fluconazole, liver toxicity can occur in as many as one in five patients.

If an adverse side effect occurs, it is expected to resolve by stopping the medication. After recovery, fluconazole can usually be restarted at a lower dose.

Itraconazole is fungicidal, meaning it kills the fungus, while fluconazole is fungistatic, which means it prevents the fungus from reproducing. The host's immune system must be strong enough to kill the fungus when the patient is on fluconazole.

If you think your pet may be having an adverse drug reaction, contact your veterinarian’s office right away.

Interactions with Other Drugs

The following medicines will be stronger when used with fluconazole and thus may have more side effects potential:

Concurrent use with cimetidine, an antacid, will reduce the effect of fluconazole.

Heart rhythm disturbances are possible with fluconazole but they are generally not significant unless the patient is also using an antibiotic of the macrolide class or cisapride, a motility modifier for the GI tract.

Fluconazole can increase the strength of cannabinoids, including CBD. This may create toxicity.

Concerns and Cautions

  • Fluconazole can be given with or without food.
  • One to two weeks are needed to get a stable blood level of fluconazole. Do not expect rapid results.
  • Fluconazole is removed from the body through the kidneys. If a patient requiring this medication has poor kidney function, dose adjustments will be necessary.

Fluconazole can penetrate most body tissues and thus fight fungal infections in most organs.

As a general rule, fungal infections are very resistant to treatment, and often months of therapy are needed.

The safety of fluconazole in pregnant dogs or cats has not been established. There may be a risk of harmful effects when given at doses higher than recommended. Fluconazole should not be used in pregnant animals unless discussed with your veterinarian. 

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