What is the appropriate antibiotic treatment for a UTI with WBC esterase 3+ and nitrite 2+, currently on fluconazole?

Treatment of Urinary Tract Infection with Positive Leukocyte Esterase and Nitrites

For a urinary tract infection with WBC esterase 3+ and nitrite 2+ in a patient currently on fluconazole, trimethoprim-sulfamethoxazole is the appropriate antibiotic treatment.

Understanding the Urinalysis Results

The urinalysis findings of leukocyte esterase 3+ and nitrite 2+ strongly indicate a bacterial urinary tract infection:

• Leukocyte esterase: Indicates presence of white blood cells in urine (pyuria)
• Nitrite positive: Suggests presence of gram-negative bacteria (particularly Enterobacteriaceae)

These findings are consistent with a bacterial UTI rather than a fungal infection, which is important to note since the patient is currently on fluconazole (an antifungal).

Treatment Algorithm

Step 1: Determine infection type

• Positive nitrites + leukocyte esterase = bacterial UTI (likely gram-negative)
• Current fluconazole therapy is not effective against bacterial pathogens

Step 2: Select appropriate antibiotic

• First-line therapy: Trimethoprim-sulfamethoxazole (TMP-SMX) 1
  • Dosage: 160mg/800mg (1 DS tablet) twice daily for 7-14 days
  • Effective against most common uropathogens including E. coli, Klebsiella, Enterobacter, and Proteus

Step 3: Special considerations

• If patient has sulfa allergy: Consider fluoroquinolone or nitrofurantoin
• If high risk for resistance: Consider broader spectrum agent like cephalosporin
• Continue fluconazole only if there is evidence of concurrent fungal infection

Evidence-Based Rationale

The Infectious Diseases Society of America guidelines recommend antibacterial therapy for symptomatic UTIs with positive leukocyte esterase and nitrite tests 2. The presence of both pyuria and nitrites has high predictive value for bacterial UTI requiring antibiotic treatment.

Fluconazole, while effective for fungal urinary tract infections 2, has no activity against bacterial pathogens. Fluconazole achieves high urinary concentrations and is the treatment of choice for Candida UTIs 3, 4, but the current urinalysis findings indicate a bacterial rather than fungal infection.

Important Clinical Considerations

• Remove predisposing factors: If the patient has an indwelling catheter, removal or replacement should be considered as this alone may resolve candiduria in up to 40% of patients 2
• Assess for complications: Evaluate for signs of upper tract involvement (fever, flank pain) which may require longer treatment duration
• Drug interactions: Be aware that fluconazole is a cytochrome P450 enzyme inhibitor and may interact with other medications 2

Common Pitfalls to Avoid

1. Misinterpreting the infection type: Positive nitrites specifically indicate bacterial infection, not fungal
2. Continuing only antifungal therapy: Fluconazole will not treat bacterial UTI despite high urinary concentrations
3. Failure to address underlying conditions: Diabetes, obstruction, or immunosuppression may predispose to recurrent infections
4. Not distinguishing between colonization and infection: Asymptomatic candiduria generally doesn't require treatment 5

In summary, the appropriate treatment for a UTI with positive leukocyte esterase and nitrites in a patient on fluconazole is trimethoprim-sulfamethoxazole, as this addresses the bacterial infection indicated by the urinalysis findings.