Fluconazole Drug Interactions: What to Avoid and What to Tell Your Doctor

Fluconazole has one of the most extensive drug interaction profiles of any commonly prescribed medication. This isn't a coincidence — it stems directly from how fluconazole works. By inhibiting key human liver enzymes (CYP2C9, CYP2C19, and CYP3A4), fluconazole interferes with the metabolism of dozens of other drugs, causing them to build up to higher levels in the blood.

Before starting fluconazole, tell your doctor and pharmacist about every medication you take — prescription, over-the-counter, supplements, and herbal products. Here's a guide to the most clinically important interactions.

Contraindicated Combinations: Do Not Take Together

These combinations are contraindicated — meaning the risk of serious harm is high enough that they should generally not be used together:

• Cisapride (Propulsid): Fluconazole inhibits the metabolism of cisapride via CYP3A4, dramatically increasing cisapride levels. This can cause dangerous QT prolongation and potentially fatal cardiac arrhythmias (torsade de pointes). This combination is contraindicated.
• Pimozide (Orap): Used for Tourette's syndrome and psychotic disorders. Fluconazole markedly increases pimozide plasma concentrations, causing QT prolongation and torsade de pointes. Contraindicated.
• Quinidine: An antiarrhythmic; the combination with fluconazole increases QT prolongation risk. Contraindicated.
• Erythromycin (at high doses): Both drugs prolong the QT interval and both affect CYP3A4. The combination significantly increases arrhythmia risk. Contraindicated at high fluconazole doses.

Major Interactions: Use With Caution and Close Monitoring

These interactions are clinically significant and require monitoring, dose adjustments, or prescriber awareness:

• Warfarin (Coumadin, Jantoven): Fluconazole strongly inhibits CYP2C9, the primary enzyme that breaks down warfarin. Even a single-dose fluconazole course can significantly raise INR. Patients on warfarin should have their INR monitored closely during and after fluconazole treatment.
• Phenytoin (Dilantin): Fluconazole inhibits CYP2C9-mediated metabolism of phenytoin, increasing phenytoin levels and the risk of toxicity (nystagmus, ataxia, confusion). Monitor phenytoin levels closely.
• Cyclosporine: Fluconazole significantly increases cyclosporine blood levels (CYP3A4 inhibition). For transplant patients on cyclosporine, this can cause nephrotoxicity. Drug levels must be monitored and doses adjusted.
• Tacrolimus: Like cyclosporine, tacrolimus levels rise significantly with fluconazole. Common co-prescription in transplant patients requiring careful monitoring.
• Simvastatin and Atorvastatin: Fluconazole inhibits the metabolism of these statins, raising their levels and increasing the risk of myopathy (muscle pain, weakness) and potentially rhabdomyolysis. Your doctor may temporarily reduce or hold statin dose.
• Amiodarone (Pacerone): Both drugs can prolong the QT interval. Combination may increase risk of serious cardiac arrhythmias. Use with caution, particularly at high fluconazole doses.
• Citalopram and Tricyclic Antidepressants: Fluconazole slows metabolism of certain antidepressants, raising their blood levels and increasing QT prolongation and serotonin syndrome risk. Discuss with your prescriber before taking fluconazole if you're on antidepressants.
• NSAIDs (Ibuprofen, Naproxen): Fluconazole can increase NSAID levels, potentially raising the risk of GI bleeding and kidney effects with regular NSAID use.
• Rifampin: Rifampin is a CYP inducer and works in the opposite direction — it speeds up fluconazole's metabolism, reducing its effectiveness. If both drugs are needed, higher fluconazole doses may be required.
• Midazolam and Triazolam (benzodiazepines): Fluconazole increases levels of these sedatives via CYP3A4 inhibition, potentiating and prolonging sedation.

Interactions With Common Blood Pressure Medications

Fluconazole can increase levels of several blood pressure medications, particularly calcium channel blockers metabolized by CYP3A4 such as amlodipine, verapamil, nifedipine, felodipine, and isradipine. Blood pressure should be monitored if fluconazole is started while taking these medications.

Losartan, an ARB blood pressure medication, is also affected — fluconazole inhibits the conversion of losartan to its active metabolite, potentially reducing blood pressure-lowering effectiveness.

Food and Supplement Interactions

• Alcohol: No formal contraindication, but alcohol increases liver stress while fluconazole is already taxing the liver. Best to avoid.
• No major food interactions: Unlike some antifungals (itraconazole requires food; voriconazole is taken fasting), fluconazole can be taken with or without food.

What to Tell Your Doctor or Pharmacist Before Starting Fluconazole

Always disclose:

• All prescription medications (especially warfarin, antiepileptics, immunosuppressants, antiarrhythmics, antidepressants, statins).
• OTC medications including NSAIDs (ibuprofen, naproxen) and antihistamines.
• Herbal supplements — St. John's Wort is a CYP inducer that can reduce fluconazole effectiveness.
• Any history of heart rhythm problems (QT prolongation, arrhythmias).
• Pregnancy or plans to become pregnant.

For a full review of fluconazole's side effect profile, see our fluconazole side effects guide. And if you need help finding a pharmacy with fluconazole in stock, medfinder.com can help.