Side Effects of Fluconazole
Fluconazole is generally well tolerated, with the most common side effects being gastrointestinal symptoms (nausea, vomiting, abdominal pain, diarrhea) and headache, occurring in 1-13% of patients. 1
Common Side Effects (Occur in >1% of patients)
Gastrointestinal effects:
- Nausea (3.7%)
- Abdominal pain (1.7%)
- Vomiting (1.7%)
- Diarrhea (1.5%)
- Dyspepsia
- Taste perversion 1
Neurologic effects:
- Headache (1.9-13%, depending on indication)
- Dizziness 1
Dermatologic effects:
- Skin rash (1.8%)
- Pruritus
- Alopecia (hair loss in scalp and pubic area) - this is a characteristic side effect of fluconazole 2
- Dry lips (74.2% in one study of coccidioidomycosis patients)
- Dry skin (45.8%) 3
Serious but Less Common Side Effects
Hepatotoxicity:
- Asymptomatic transaminase elevations (1-13% of patients) 2
- Clinical hepatitis (rare)
- Fulminant hepatic failure (rare, primarily in patients with serious underlying conditions like AIDS or malignancy) 1
- Fatal hepatitis has been reported rarely 2
Warning signs of serious liver problems include: dark urine, light-colored stools, severe itching, jaundice, loss of appetite, and fatigue 1
Severe allergic reactions:
- Anaphylaxis (rare)
- Angioedema
- Stevens-Johnson syndrome (rare cases reported) 2
- Serious skin reactions that can be fatal 1
Hematologic abnormalities:
- Thrombocytopenia
- Leukopenia (reported with itraconazole but can occur with fluconazole) 2
Cardiovascular:
Other serious effects:
- Seizures 1
- Adrenal insufficiency (reversible) 1
- Retinal toxicity (cystoid macular edema reported with high prolonged doses) 5
Important Drug Interactions
Fluconazole inhibits cytochrome P450 enzymes (particularly CYP3A4, CYP2C9, and CYP2C19), leading to significant drug-drug interactions 2, 4, 2, 4. This can result in:
- Increased plasma concentrations of co-administered drugs (potentially causing toxicity)
- Decreased fluconazole levels if combined with enzyme inducers
Critical interactions occur with: antiretroviral drugs, immunosuppressants (cyclosporine, tacrolimus), cardiac medications (quinidine, pimozide), statins, warfarin, and many others 4, 1
Clinical Considerations
- HIV-infected patients experience adverse events more frequently (21%) than non-HIV infected patients (13%), though patterns are similar 1
- Treatment discontinuation due to adverse events occurs in approximately 1.5% of patients 1
- Long-term, high-dose therapy (≥300-600 mg/day for ≥6 months) appears well tolerated, with 27% experiencing symptomatic side effects and 42% having asymptomatic laboratory abnormalities 6
- Patients should avoid driving or operating machinery until they know how fluconazole affects them due to potential dizziness and seizures 1
The most recent comprehensive guideline 4 emphasizes that fluconazole and posaconazole are generally well tolerated with serious adverse events (primarily liver toxicity) being rare, making fluconazole one of the safer azole antifungals for most patients.