Diflucan (Fluconazole)

Diflucan contains fluconazole, a triazole antifungal that inhibits fungal ergosterol synthesis to treat Candida infections and cryptococcal meningitis. It requires a prescription and is available as 50mg to 200mg tablets, oral suspension and IV injection.

• Dose: 150mg single for vaginal; 200mg daily for oropharyngeal/esophageal; 400mg loading for meningitis
• Status: Prescription required, triazole antifungal
• Primary use: Candidiasis, cryptococcal meningitis, bone marrow transplant prophylaxis
• Half-life: 30 hours in adults with normal kidney function, steady state in 5 to 7 days

What Is Diflucan

Diflucan is the brand name for fluconazole, a triazole antifungal approved by the FDA for Candida infections and cryptococcal meningitis. It is available as 50mg, 100mg, 150mg and 200mg tablets, oral suspension and intravenous injection. Generic fluconazole is bioequivalent to the brand formulation.

Fluconazole is a white crystalline powder with high water solubility. Oral bioavailability exceeds 90 percent. Food does not affect absorption. Peak plasma concentration occurs within 1 to 2 hours. The half-life is 30 hours in adults with normal kidney function. It is longer in patients with renal impairment. Steady-state concentrations are reached after 5 to 7 days of daily dosing. Fluconazole is eliminated primarily through the kidneys as unchanged drug. A 3-hour hemodialysis session decreases plasma fluconazole levels by 50 percent.

How Diflucan Works

Fluconazole inhibits fungal cytochrome P450 enzyme lanosterol 14-alpha-demethylase, which converts lanosterol to ergosterol. Without ergosterol, the fungal cell membrane becomes permeable and cellular contents leak out, killing the cell. Fluconazole is selective for fungal enzymes but does inhibit human CYP2C9 and CYP3A4 at therapeutic doses.

Key mechanisms:

• Ergosterol synthesis inhibition: Blocks lanosterol 14-alpha-demethylase. Depletes membrane ergosterol.
• Membrane permeabilization: Fungal cell membrane loses integrity. Cellular contents leak.
• Fungistatic action: Inhibits growth and replication of susceptible Candida species.
• CYP enzyme inhibition: Explains clinically significant drug interactions with warfarin, phenytoin and immunosuppressants.

Conditions Treated by Diflucan

The FDA approved fluconazole for five primary indications. Dosing varies by infection type, severity and patient immune status. Vaginal candidiasis requires a single dose, while cryptococcal meningitis needs months of therapy. Doctors also use fluconazole off-label for systemic Candida infections including candidemia and disseminated candidiasis.

• Vaginal candidiasis: A single 150mg oral dose. Therapeutic cure rate is 55 percent at one month. Clinical cure is 69 percent. Mycologic eradication is 61 percent. Results are comparable to 7-day topical azole therapy.
• Oropharyngeal candidiasis: 200mg on the first day, then 100mg once daily. Treat for at least 2 weeks. Clinical evidence usually resolves within several days. Longer courses decrease relapse.
• Esophageal candidiasis: 200mg on the first day, then 100mg once daily. Doses up to 400mg daily may be used. Treat for a minimum of 3 weeks and at least 2 weeks after symptoms resolve.
• Cryptococcal meningitis: 400mg on the first day, then 200mg once daily. Treat for 10 to 12 weeks after cerebrospinal fluid becomes culture negative. Patients with AIDS require lifelong suppression at 200mg daily to prevent relapse.
• Prophylaxis in bone marrow transplantation: 400mg once daily. Start several days before anticipated neutropenia. Continue for 7 days after neutrophil count rises above 1000 cells per cubic millimeter.

Fluconazole is also used off-label for systemic Candida infections including candidemia and disseminated candidiasis. Doses up to 400mg daily have been used. For Candida urinary tract infections and peritonitis, daily doses of 50 to 200mg have been used. Optimal dosing for systemic infections is not established. Patients with other infections should tell their doctor before starting Diflucan. Underlying conditions affect dosing and duration.

Diflucan Dosage and Strengths

Manufacturers produce fluconazole in three delivery forms: tablets, oral suspension and intravenous injection. Six tablet strengths exist, from 50mg maintenance doses to 200mg loading doses. Oral and IV dosing are identical because absorption exceeds 90 percent. This makes IV-to-oral stepdown seamless for hospitalized patients.

Available Forms

• 50mg tablets: Low-dose maintenance for prophylaxis or mild infections.
• 100mg tablets: Standard maintenance dose for oropharyngeal and esophageal candidiasis.
• 150mg tablets: Single-dose therapy for vaginal candidiasis.
• 200mg tablets: Loading dose for oropharyngeal and esophageal candidiasis. Maintenance dose for cryptococcal meningitis suppression.
• Oral suspension: 10mg per mL or 40mg per mL. Alternative for patients who cannot swallow tablets.
• Intravenous injection: For hospitalized patients who cannot take oral medication. Same dosing as oral.

Standard Adult Dosing by Indication

For vaginal candidiasis, take 150mg as a single oral dose. One tablet is usually sufficient. A second dose may be needed if symptoms persist.

For oropharyngeal candidiasis, take 200mg on the first day. Then take 100mg once daily. Continue for at least 2 weeks. This decreases relapse likelihood.

For esophageal candidiasis, take 200mg on the first day. Then take 100mg once daily. Continue for a minimum of 3 weeks. Continue for at least 2 weeks after symptoms resolve. Doses up to 400mg daily may be used based on response.

For cryptococcal meningitis, take 400mg on the first day. Then take 200mg once daily. Continue for 10 to 12 weeks after CSF becomes culture negative. For AIDS patients, continue 200mg daily as lifelong suppression to prevent relapse.

For bone marrow transplant prophylaxis, take 400mg once daily. Start several days before anticipated neutropenia. Continue for 7 days after neutrophil count rises above 1000 cells per cubic millimeter.

Renal Dose Adjustment

Fluconazole is cleared primarily by the kidneys. Dose adjustment is required for multiple-dose therapy in patients with renal impairment. Single-dose therapy for vaginal candidiasis does not require adjustment.

• Creatinine clearance above 50 mL per minute: 100 percent of recommended dose.
• Creatinine clearance 50 mL per minute or below, no dialysis: 50 percent of recommended dose.
• Hemodialysis patients: 100 percent of recommended dose after each dialysis session. Reduced dose on non-dialysis days based on creatinine clearance.

Missed Dose Instructions

Take the missed dose when you remember. If you are on a once-daily regimen and the next dose is within 6 hours, skip the missed dose. Do not double the dose. Doubling increases the risk of hepatotoxicity and QT prolongation. Resume the normal schedule. For single-dose therapy, there is no maintenance schedule to resume.

Side Effects

Most patients tolerate fluconazole well. Side effects are usually mild and resolve after treatment ends. FDA clinical trials report specific documented incidence rates for nausea, headache and abdominal pain. Serious adverse events include hepatotoxicity, QT prolongation and severe skin reactions.

Common Side Effects

• Nausea (2.3 percent of patients)
• Headache (2 percent)
• Abdominal pain (2.8 percent)
• Diarrhea (2.1 percent)
• Rash
• Dizziness
• Dyspepsia
• Vomiting (5.4 percent in pediatric patients)

Serious Side Effects

Stop taking Diflucan and contact a doctor immediately if you experience:

• Hepatotoxicity: yellowing skin, dark urine, severe fatigue, right upper quadrant pain. Elevated transaminases occur in some patients. Stop fluconazole immediately if liver dysfunction develops. Risk increases with prolonged therapy and higher doses.
• QT prolongation and torsades de pointes: irregular heartbeat, fainting, palpitations. Risk increases in patients with existing heart conditions, electrolyte abnormalities and concurrent QT-prolonging drugs. ECG monitoring may be needed.
• Stevens-Johnson syndrome or toxic epidermal necrolysis: widespread skin rash, blistering, peeling. Stop immediately and seek emergency care.
• Anaphylaxis: difficulty breathing, facial swelling, hives, rapid heartbeat. Seek emergency care immediately.
• Exfoliative dermatitis: severe skin redness and peeling. Stop fluconazole and seek medical attention.
• Seizures: convulsions or loss of consciousness. Report immediately.

Who Should Not Take Diflucan

Do not take Diflucan if you have hypersensitivity to fluconazole or other azole antifungals. Avoid it if you take cisapride, terfenadine or astemizole due to fatal cardiac arrhythmia risk. Fluconazole increases plasma levels of these drugs and causes fatal torsades de pointes.

Do not take high-dose fluconazole (400 to 800mg daily) during the first trimester of pregnancy. The FDA assigns Category D for chronic high-dose use. It causes craniofacial, skeletal and heart defects. The CDC recommends avoiding fluconazole in pregnancy. Use topical azoles instead. A single 150mg dose for vaginal candidiasis may carry lower risk but should still be discussed with an OB-GYN. Do not take if you are breastfeeding without medical consultation. Fluconazole passes into breast milk at concentrations similar to maternal plasma.

Warnings and Precautions

Fluconazole can cause liver damage and QT prolongation. Monitor liver function tests before and during prolonged courses. Obtain a baseline ECG if cardiac risk factors exist. Avoid other QT-prolonging drugs during fluconazole therapy. Risk factors include existing QT prolongation, hypokalemia, hypomagnesemia and female sex.

Hepatotoxicity

Fluconazole can cause liver damage. Monitor liver function tests before starting therapy and periodically during prolonged courses. Stop fluconazole if transaminases rise significantly or if jaundice develops. Risk is higher with daily doses above 200mg and treatment courses longer than 2 weeks. Patients with pre-existing liver disease require closer monitoring.

QT Prolongation and Cardiac Arrhythmias

Fluconazole prolongs the QT interval in susceptible patients. This increases the risk of torsades de pointes, a life-threatening ventricular arrhythmia. Risk factors include existing QT prolongation, hypokalemia, hypomagnesemia, concurrent QT-prolonging drugs and female sex. Obtain a baseline ECG if risk factors exist. Monitor electrolytes. Avoid other QT-prolonging drugs during fluconazole therapy.

Drug Interactions

Fluconazole inhibits CYP2C9 and CYP3A4. This increases plasma levels of many medications. Always provide your doctor with a complete medication list.

• Warfarin: INR increases significantly. Monitor closely. Bleeding risk rises.
• Phenytoin: Fluconazole increases phenytoin levels. Phenytoin also increases fluconazole metabolism. Monitor phenytoin levels and adjust doses.
• Cyclosporine and tacrolimus: Fluconazole increases immunosuppressant levels. Nephrotoxicity risk rises. Monitor trough levels.
• Oral hypoglycemics (sulfonylureas): Fluconazole increases hypoglycemic effect. Monitor blood glucose. Adjust antidiabetic dose.
• Statins (atorvastatin, simvastatin): Fluconazole increases statin levels. Myopathy and rhabdomyolysis risk rises. Use lowest statin dose or switch to pravastatin.
• Cisapride, terfenadine, astemizole: Contraindicated. Fatal QT prolongation.
• Quinidine, erythromycin: Additive QT prolongation. Avoid unless specifically directed.
• Rifampin: Decreases fluconazole levels. May require dose increase.

Pediatric Use

Diflucan is approved for children 6 months and older for oropharyngeal candidiasis. For esophageal candidiasis, systemic Candida infections and cryptococcal meningitis, efficacy is supported by adult data and small pediatric studies. Dosing is weight-based. Premature infants weighing less than 750 grams have a higher risk of intestinal perforation with fluconazole prophylaxis. Use caution in neonates. Full-term newborn pharmacokinetics are not established.

Diflucan and Pregnancy

High-dose fluconazole (400 to 800mg daily) is contraindicated during the first trimester. The FDA assigns Category D for chronic high-dose use due to craniofacial and cardiac birth defects. A Danish cohort study found an association with tetralogy of Fallot. The National Birth Defects Prevention Study found associations with cleft lip and dextro-transposition of the great arteries.

Low-dose single 150mg for vaginal candidiasis may carry lower risk. Most epidemiologic studies found no increased risk with low-dose exposure. However, the CDC recommends avoiding fluconazole in pregnancy. Use topical azoles such as clotrimazole or miconazole instead. If fluconazole is used, discuss risks with an OB-GYN.

Fluconazole passes into breast milk at concentrations similar to maternal plasma. Caution is advised during breastfeeding. Discuss risks and benefits with your doctor. Topical antifungals may be preferred for nursing mothers.

Overdose Information

Overdose symptoms include hallucinations, paranoid behavior, nausea, vomiting and diarrhea. Very high doses cause seizures, QT prolongation and hepatic failure. Fluconazole is largely excreted in urine. A 3-hour hemodialysis session decreases plasma levels by 50 percent. Treatment is supportive. Contact poison control at 1-800-222-1222. Seek emergency care for severe symptoms.

Diflucan vs Itraconazole

Diflucan and itraconazole are both triazole antifungals but differ in spectrum, pharmacokinetics and drug interactions. Fluconazole is water-soluble with excellent oral bioavailability and CSF penetration. Itraconazole is lipophilic, requires food for absorption and covers Aspergillus. Choose fluconazole for Candida infections and cryptococcal meningitis.

Choose itraconazole for Aspergillus infections, dermatophyte infections and when broader spectrum is needed. Both require prescription monitoring. Both carry hepatotoxicity risk. Fluconazole penetrates the cerebrospinal fluid well. This makes it the preferred treatment for cryptococcal meningitis. It has a long half-life of 30 hours. It is primarily renally excreted. Dose adjustment is needed for renal impairment. It inhibits CYP2C9 and CYP3A4. It interacts with warfarin, phenytoin and statins.

Itraconazole has poor CSF penetration. It is not used for meningitis. It has a broader spectrum including Aspergillus and dermatophytes. It is metabolized by CYP3A4. It has more drug interactions than fluconazole. It requires therapeutic drug monitoring. It is not first-line for Candida infections.

Storage and Handling

Store Diflucan tablets at room temperature between 20C and 25C. Keep away from moisture and heat. Do not store in the bathroom. Keep out of reach of children. Discard expired products. Do not use if the seal is broken. Store oral suspension between 5C and 30C. Discard unused suspension after 2 weeks. Protect from freezing.

Frequently Asked Questions

Sources and References

• U.S. Food and Drug Administration – DIFLUCAN (fluconazole) Tablets Prescribing Information, NDA 019949
• DailyMed – Fluconazole Tablets and Oral Suspension Drug Label, National Library of Medicine, Updated 2024
• PubMed – Fluconazole – StatPearls. NCBI Bookshelf, 2024
• PMC – Molgaard-Nielsen D et al. Birth defects after fluconazole use in pregnancy. BMJ, 2013
• Centers for Disease Control and Prevention – Vulvovaginal Candidiasis Treatment Guidelines, 2025