Fungal Infections Dogs, Fluconazole (Diflucan), 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 represent vast improvement over 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 three 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 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. The third reason is expense when compared to itraconazole. 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:
- Dermatophytosis (ringworm) although it is usually reserved for more serious fungal disease.
- Cryptococcosis (window washer’s disease)
- Aspergillosis (conflicting agreement as to whether it is effective or not against this fungal infection)
- Coccidioidomycosis (Valley Fever)
- Malassezia dermatitis (yeast infection of the skin)
- 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 timed accordingly.
While fluconazole users do not commonly experience side effects, it is important to be aware of 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 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, notify your veterinarian’s office right away.
Interactions with other Drugs
The following heart medicines will be stronger when used with fluconazole and thus may have more side effects potential:
- Buspirone, an antianxiety medication
- Corticosteroids, used for inflammation and to suppress the immune system in numerous scenario
- Cyclophosphamide, a chemotherapy drug
- Cyclosporine, an immunomodulator used for atopic dermatitis, immune mediated hemolytic anemia, thrombocytopenia, and other immune-mediated diseases.
- Fentanyl, a narcotic pain reliever
- Non-steroidal anti-inflammatories (NSAIDs), pain relievers
- Quinidine, a heart medication
- Rifampin, an antibiotic
- Theophylline, an oral airway dilator
- Vincristine, a chemotherapy drug
- Benzodiazepines – used for anxiety and panic.
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.
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 is able to penetrate most body tissues and thus fight fungal infections in most organs.
Fungal infections as a general rule are very resistant to treatment and often months of therapy are needed.
Fluconazole is dangerous if given in pregnancy. If a pet is pregnant, fluconazole should be avoided unless the fungal infection in question is potentially life-threatening.
Fluconazole should also be avoided in lactation as it will be delivered through milk to any nursing young.
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