Vet Guide to Fluconazole in 2025 🐾

Hello, I’m **Dr Duncan Houston, BVSc**, founder of Ask A Vet. This in‑depth 2025 guide covers everything you need to know about **fluconazole**, a triazole antifungal prescribed off-label in pets to treat systemic fungal infections—such as cryptococcosis, histoplasmosis, and blastomycosis—plus dermatophytes, yeast, and CNS fungal disease. Learn about dosing, safety measures, side‑effects, drug interactions, and monitoring to support your pet’s recovery. 💊🐶🐱

📘 What Is Fluconazole?

Fluconazole (brand: Diflucan®) is a triazole antifungal that inhibits fungal cell membrane synthesis. It has excellent oral bioavailability and penetrates deeply—including the central nervous system—and is fungistatic to many yeasts and some molds :contentReference[oaicite:3]{index=3}.

✅ Approved vs. Extra‑Label Uses

• FDA-approved for humans, but used off-label in pets under veterinary guidance :contentReference[oaicite:4]{index=4}.
• Used in dogs for cryptococcosis, valley fever, aspergillosis, blastomycosis, histoplasmosis, candidiasis, and dermatophytosis :contentReference[oaicite:5]{index=5}.
• In cats, especially used for cryptococcosis and systemic fungal disease, including CNS involvement :contentReference[oaicite:6]{index=6}.
• Also effective for skin and nail yeast infections in both species :contentReference[oaicite:7]{index=7}.

📐 Dosing & Administration

• Dogs: 5–10 mg/kg orally every 12–24 hours, depending on infection severity; typically 10 mg/kg q12h for CNS or deep infections :contentReference[oaicite:8]{index=8}.
• Cats: Generally 10 mg/kg once daily (~50 mg per cat); higher dosage may be used for CNS infections based on veterinary supervision :contentReference[oaicite:9]{index=9}.
• Available as tablets (50–200 mg), compounded liquid, and injectable forms for hospitalized cases :contentReference[oaicite:10]{index=10}.
• Can be given with or without food; giving with food may reduce GI upset :contentReference[oaicite:11]{index=11}.
• For missed doses, administer as soon as remembered; do not double dose :contentReference[oaicite:12]{index=12}.
• Treatment duration is often long—4–8 weeks for dermatophytes and 2+ months beyond symptom resolution for systemic disease :contentReference[oaicite:13]{index=13}.

⚠️ Side‑Effects & Liver Safety

• Mild, common: reduced appetite, vomiting, diarrhea, soft stools, lethargy, dry skin, or mild hair loss :contentReference[oaicite:14]{index=14}.
• Serious (rare): liver toxicity or hepatitis, seen as anorexia, jaundice, elevated liver enzymes; requires prompt veterinary attention :contentReference[oaicite:15]{index=15}.
• Hematologic signs (e.g. anemia) are rare but possible :contentReference[oaicite:16]{index=16}.

🚫 Contraindications & Precautions

• Avoid in pets with known fluconazole allergy or hypersensitivity :contentReference[oaicite:17]{index=17}.
• Use with caution or dosage adjustment in pets with pre-existing liver or kidney disease :contentReference[oaicite:18]{index=18}.
• Use cautiously in pregnant or nursing pets; benefit vs. risk should be evaluated :contentReference[oaicite:19]{index=19}.

🔗 Drug Interactions

Fluconazole inhibits CYP450 enzymes, affecting metabolism of numerous drugs—inform your vet about all medications, including:

• Warfarin, NSAIDs, opioids (e.g. fentanyl), benzodiazepines, buspirone, cimetidine, cisapride, corticosteroids, cyclophosphamide, cyclosporine, rifampin, theophylline, etc. :contentReference[oaicite:20]{index=20}.

🩺 Monitoring & Veterinary Follow‑Up

• Baseline and periodic blood tests (CBC, liver enzymes, kidney values) during long-term therapy :contentReference[oaicite:21]{index=21}.
• Watch for GI signs, lethargy, appetite loss, jaundice—report promptly to your vet :contentReference[oaicite:22]{index=22}.
• Recheck or culture fungal sites (e.g. cryptococcal antigen titers) to confirm effective disease control before stopping :contentReference[oaicite:23]{index=23}.

🏡 Case Examples

🐶 Dog with CNS blastomycosis

• Started on fluconazole 10 mg/kg q12h, switched to once daily after 2 weeks based on plasma levels; neurologic improvement by week 4; treatment continued for 6 months post-resolution.

🐱 Cat with cryptococcal rhinitis

• Administered 10 mg/kg once daily; nasal signs improved steadily over 3 weeks; antigen testing became negative after 4 months—treatment stopped after additional 2 months.

❓ FAQs

Why is therapy so long?

Fungal infections are slow to resolve and require prolonged treatment to prevent relapse. Therapy often extends weeks to months beyond symptom resolution :contentReference[oaicite:24]{index=24}.

Can I stop early if pet seems better?

No—early discontinuation risks relapse and resistance. Always follow your vet’s recommended duration and monitoring protocol :contentReference[oaicite:25]{index=25}.

Can I give it with food?

Yes. Although food doesn’t reduce absorption significantly, giving it with a small meal can reduce GI upset :contentReference[oaicite:26]{index=26}.

📌 Final Takeaways

• Fluconazole is a key antifungal used off-label in pets, effective for systemic, CNS, skin, and ear fungal infections.
• Dosing: dogs 5–10 mg/kg q12–24h; cats ~10 mg/kg once daily. Duration often spans months.
• Monitor for mild GI signs—rare serious liver-related effects may occur.
• Many drug interactions require veterinary oversight.
• Use bloodwork and fungal testing to guide safe, effective treatment through to full resolution. 🐾❤️

Considering fluconazole for your pet’s fungal infection? Download the Ask A Vet app for dosage calculators, liver monitoring alerts, drug interaction warnings, and 24/7 veterinary support—helping your pet stay healthy and fungus-free in 2025. 💊🐶🐱