What is the recommended dose of fluconazole (Fluconazole) for an adult patient with a fungal urinary tract infection (UTI) and potential impaired renal function?

Fluconazole Dosing for Fungal UTI

For symptomatic fungal cystitis, use fluconazole 200 mg daily for 2 weeks; for pyelonephritis, use 200-400 mg daily for 2 weeks; adjust dose by 50% if GFR <45 mL/min/1.73 m². 1, 2, 3

Dosing by Clinical Presentation

Symptomatic Cystitis (Bladder Infection)

• Fluconazole 200 mg (3 mg/kg) orally daily for 2 weeks is the standard dose for fluconazole-susceptible organisms 1, 2
• Remove indwelling catheters immediately if present, as catheter removal alone resolves candiduria in approximately 50% of cases 2, 3
• For fluconazole-resistant C. glabrata or C. krusei, switch to amphotericin B deoxycholate 0.3-0.6 mg/kg daily for 1-7 days OR flucytosine 25 mg/kg four times daily for 7-10 days 1, 2

Pyelonephritis (Kidney Infection)

• Fluconazole 200-400 mg (3-6 mg/kg) orally daily for 2 weeks for fluconazole-susceptible organisms 1, 2
• The higher end of the dosing range (400 mg daily) should be used for more severe infections or when there is concern about dissemination 1, 2
• Remove or replace any urinary obstruction devices (nephrostomy tubes, stents) whenever feasible 2
• If disseminated candidiasis is suspected, treat as candidemia with higher doses and longer duration 1

Asymptomatic Candiduria

• Do not treat unless the patient is neutropenic, a very low-birth-weight infant, or undergoing urologic procedures 1, 2
• Remove predisposing factors (catheters, unnecessary antibiotics) first, which clears candiduria in ~50% of asymptomatic patients 2

Patients Undergoing Urologic Procedures

• Fluconazole 400 mg (6 mg/kg) daily OR amphotericin B deoxycholate 0.3-0.6 mg/kg daily for several days before and after the procedure 1, 2

Renal Dose Adjustments

Impaired Renal Function (Not on Dialysis)

• Reduce the maintenance dose by 50% when GFR <45 mL/min/1.73 m², as fluconazole is 60% renally excreted unchanged 3
• For example, if the standard dose is 200 mg daily, reduce to 100 mg daily when GFR <45 mL/min/1.73 m² 3
• If the standard dose is 400 mg daily, reduce to 200 mg daily when GFR <45 mL/min/1.73 m² 3

Hemodialysis Patients

• Administer 200 mg after each hemodialysis session for symptomatic candiduria 3
• The elimination half-life is prolonged in renal insufficiency, requiring dosage adjustment based on creatinine clearance 4

Peritoneal Dialysis (CAPD) Patients

• Use 50 mg intraperitoneally or 100 mg orally for fungal peritonitis 5
• Alternatively, 150 mg in a 2L dialysis solution every 2 days has been proposed 4

Loading Dose Considerations

• A loading dose equal to double the maintenance dose is recommended because fluconazole has a long half-life (31-37 hours) and requires 6 days to reach steady-state 4
• For example, if using 200 mg daily maintenance, give 400 mg on day 1 4
• One study suggested a 200 mg loading dose followed by 100 mg daily for at least 4 days for symptomatic candidal UTI without systemic infection 6

Critical Pitfalls to Avoid

• Never treat asymptomatic candiduria in immunocompetent patients, as this leads to unnecessary antifungal exposure and potential resistance development 2
• Failure to remove catheters significantly reduces treatment success—catheter removal is as important as antifungal therapy itself 2, 3
• Bladder irrigation with amphotericin B has high relapse rates and should only be used as adjunctive therapy for refractory fluconazole-resistant organisms 1, 2
• Do not use fluconazole in patients with prior azole prophylaxis or recent azole exposure, as resistance is more likely 1
• Monitor for fluconazole resistance during therapy, particularly with C. glabrata, and consider follow-up cultures if clinical improvement is not observed 3

Drug Interactions in Renal Impairment

• Reduce warfarin dose and monitor INR closely, particularly when GFR <30 mL/min/1.73 m², as fluconazole potentiates warfarin's anticoagulant effect and bleeding risk increases 3