Fluconazole (Diflucan) for Yeast Infections: Dosage, Duration & Safety

Fluconazole is a triazole antifungal used for mucosal and systemic Candida infections. It is not FDA-approved for penile yeast infections in men (topical azoles are standard), but widely used off-label for recurrent balanitis.

Standard Dosing Regimens

Infection Type	Dose & Duration
Vulvovaginal Candidiasis (uncomplicated)	Single 150 mg oral dose
Recurrent VVC (≥3/year)	150 mg every 72h x 3 doses (induction), then weekly x 6 months (maintenance)
Oropharyngeal Candidiasis (Thrush)	200 mg day 1, then 100 mg daily x 7–14 days
Esophageal Candidiasis	200 mg day 1, then 100 mg daily x 14–21 days (continue 2 wks after resolution)
Candida UTI / Cystitis	200 mg daily x 7–14 days
Systemic/Invasive Candidiasis	400–800 mg (6–12 mg/kg) daily; duration 2+ weeks after last positive culture
Cryptococcal Meningitis	400 mg day 1, then 200–400 mg daily x 8+ weeks (with amphotericin induction)
Prophylaxis (immunocompromised)	100–400 mg daily/weekly per protocol

Key Pharmacokinetics

• Excellent oral bioavailability (>90%) – oral = IV dosing.
• Penetrates CSF, saliva, urine, vaginal secretions well.
• Renal elimination: Dose adjustment required for CrCl <50 mL/min (reduce by 50%).
• Long half-life (~30h) allows once-daily/weekly dosing.

Side Effects & Monitoring

• Common (1–5%): Headache, nausea, abdominal pain, diarrhea, rash, transaminitis (ALT/AST elevation).
• Serious/Rare:
  • Hepatotoxicity (fulminant liver failure – monitor LFTs in prolonged/high-dose therapy)
  • QT prolongation / Torsades de Pointes (avoid with other QT-prolonging drugs)
  • Stevens-Johnson Syndrome / TEN (rare, severe cutaneous adverse reaction)
  • Adrenal insufficiency (inhibits cortisol synthesis – relevant in critically ill)
• Drug Interactions (CYP2C9/3A4 inhibitor): Warfarin (↑INR), Statins (↑myopathy), Sulfonylureas (↑hypoglycemia), Phenytoin, Theophylline, Tacrolimus, Cisapride (contraindicated). Always review med list.

Special Populations

• Pregnancy: Single 150 mg dose (VVC) generally safe (Category C/D at high doses). Avoid chronic high-dose (teratogenicity risk). Topical preferred.
• Breastfeeding: Compatible (low milk levels); monitor infant for GI effects.
• Pediatrics: Dosed by weight (3–12 mg/kg); approved ≥6 months for some indications.

Important Reminders

• Complete full course even if symptoms improve—prevents resistance/relapse.
• Symptom relief typically within 24–72h for VVC.
• If no improvement in 3–5 days, re-evaluate diagnosis (bacterial vaginosis, trichomonas, dermatoses).
• Recurrent VVC requires confirmation (culture + speciation) – non-albicans species (C. glabrata) resist fluconazole; need boric acid/flucytosine.