What is the recommended treatment, dosing, duration, and monitoring for a symptomatic Candida krusei urinary tract infection, including adjustments for impaired renal function?

Treatment of Candida krusei Urinary Tract Infection

For symptomatic C. krusei UTI, amphotericin B deoxycholate 0.3-0.6 mg/kg IV daily for 1-7 days is the recommended first-line treatment, with mandatory removal of any indwelling bladder catheter if present. 1

Initial Assessment and Risk Stratification

Before initiating treatment, confirm this represents true infection rather than asymptomatic colonization by evaluating for:

• Urinary symptoms (dysuria, frequency, urgency, flank pain, fever) 2
• High-risk features: neutropenia, very low birth weight (<1500g in neonates), or planned urologic procedures 1
• Presence of indwelling catheter or urinary obstruction 1

Treatment is warranted for symptomatic patients, while asymptomatic candiduria should NOT be treated unless high-risk features are present. 1, 2

Treatment Algorithm by Infection Site

For Cystitis (Lower UTI)

Primary therapy:

• Amphotericin B deoxycholate 0.3-0.6 mg/kg IV daily for 1-7 days 1
• Duration: Complete 2 weeks of therapy 2
• Remove indwelling bladder catheter immediately if present (this is mandatory, not optional) 1

Alternative option for cystitis only:

• Amphotericin B bladder irrigation: 50 mg/L sterile water daily for 5 days 1
• This approach is useful only when systemic therapy cannot be used and infection is confirmed to be limited to the bladder 1
• Note: Bladder irrigation has high recurrence rates (recurrence within weeks is very common) and should be combined with endoscopic removal of any obstructing lesions 1

For Pyelonephritis (Upper UTI)

Primary therapy:

• Amphotericin B deoxycholate 0.3-0.6 mg/kg IV daily for 1-7 days 1
• Duration: 2 weeks total after symptom resolution 2
• Eliminate any urinary tract obstruction (surgical consultation if hydronephrosis or obstruction present) 1
• Remove or replace nephrostomy tubes/stents if feasible 1

For nephrostomy tube irrigation (if tubes present):

• Amphotericin B deoxycholate 25-50 mg in 200-500 mL sterile water through the tube 1

Why Fluconazole Cannot Be Used

C. krusei exhibits intrinsic resistance to fluconazole, making it completely ineffective for this organism. 1, 3 This is a critical distinction from other Candida species where fluconazole would be first-line. 1, 4

Why Echinocandins Are Not Recommended for UTI

Echinocandins (caspofungin, micafungin, anidulafungin) achieve minimal urinary concentrations and are generally ineffective for urinary tract infections, despite being first-line for invasive candidiasis and candidemia. 1, 4, 5 There are isolated case reports of success with high-dose micafungin (150 mg daily) for refractory cases in transplant patients, but this remains off-guideline. 3

Dosing Adjustments for Renal Impairment

Amphotericin B deoxycholate:

• No dose adjustment required for renal impairment (the drug itself is nephrotoxic, but dosing remains the same) 1
• Monitor renal function closely: baseline and every 2-3 days during therapy
• Monitor electrolytes (particularly potassium and magnesium) at least twice weekly
• Consider pre-hydration with normal saline to reduce nephrotoxicity

Flucytosine (if used as alternative):

• Requires significant dose reduction in renal impairment
• Not recommended as monotherapy due to rapid resistance development 1
• Has poor activity against C. krusei specifically 1

Monitoring Requirements

During treatment:

• Repeat urine cultures every 2-3 days until clearance documented 2
• Monitor serum creatinine, BUN, potassium, and magnesium at least twice weekly during amphotericin B therapy
• Monitor complete blood count weekly (amphotericin B can cause anemia)

Treatment endpoints:

• Negative urine cultures (clearance documented)
• Resolution of symptoms (fever, dysuria, flank pain)
• Complete 2 weeks of therapy after clearance for cystitis 2
• Complete 2 weeks of therapy after symptom resolution for pyelonephritis 2

Critical Pitfalls to Avoid

Do not use fluconazole - C. krusei has intrinsic resistance and treatment will fail. 1, 3

Do not use echinocandins - Despite being excellent for candidemia, they do not achieve adequate urinary concentrations. 1, 4

Do not use lipid formulations of amphotericin B (liposomal amphotericin, amphotericin B lipid complex) - These do not achieve adequate urine concentrations and should not be used for UTI. 1

Do not continue treatment without removing the catheter - Failure to remove indwelling catheters is associated with treatment failure and recurrence. 1

Do not assume asymptomatic candiduria requires treatment - Most candiduria represents colonization, and treatment does not improve outcomes in asymptomatic patients unless they are high-risk. 1

Special Considerations for Fungus Balls

If imaging reveals fungus balls (aggregations of mycelia and yeasts causing obstruction):

• Surgical or endoscopic removal is mandatory - antifungal therapy alone will not succeed. 1
• Combine surgical intervention with systemic antifungal therapy as outlined above 1
• Consider nephrostomy tube irrigation with amphotericin B if tubes are placed 1