What is the best antibiotic choice for Aerococcus urinae urinary tract infection (UTI) when sensitivities are not available?

Best Antibiotic Choice for Aerococcus urinae UTI Without Sensitivities

For Aerococcus urinae urinary tract infection when sensitivities are not available, nitrofurantoin is the recommended first-line treatment option due to its demonstrated clinical and microbiological efficacy.

Understanding Aerococcus urinae

Aerococcus urinae is an emerging uropathogen that is increasingly recognized as a cause of urinary tract infections, particularly in:

• Older adults
• Patients with multimorbidity
• Those with urologic conditions or chronic urinary retention
• Patients with indwelling catheters

Treatment Recommendations

First-line options:

1. Nitrofurantoin

   • Dosage: 100 mg twice daily for 5-7 days
   • Clinical success rate: 71% for A. urinae UTI 1
   • Microbiological success rate: 76% for A. urinae UTI 1
   • Advantages: High urinary concentrations, low resistance rates (100% susceptibility reported) 2

2. Penicillins/Ampicillin

   • Excellent in vitro activity against A. urinae (100% susceptibility) 2
   • Appropriate for patients who cannot tolerate nitrofurantoin

Alternative options:

1. Fosfomycin

   • Dosage: 3 g single-dose sachet
   • Consider for uncomplicated lower UTI
   • Recommended as a first-line agent for uncomplicated UTIs 3

2. Pivmecillinam

   • Has shown success in treating A. urinae cystitis 1
   • May be considered if other options are unavailable

For complicated UTI or pyelonephritis:

1. Fluoroquinolones (e.g., Ciprofloxacin)

   • Should be used cautiously due to:
     • Increasing resistance rates (10.9% resistance reported) 2
     • Risk of collateral damage 3
   • Only use if local resistance rate is <10% 3
   • Consider for pyelonephritis cases 1

2. Ceftriaxone

   • For severe infections requiring parenteral therapy
   • Dosage: 1-2 g IV daily 3

Treatment Duration

• For uncomplicated cystitis: 5-7 days 3
• For complicated UTI: 7-14 days 3
• For pyelonephritis: 7-14 days 3

Important Considerations

• Obtain urine culture before initiating therapy whenever possible 3
• A. urinae may be misidentified by some commercial detection systems 4
• If the patient has an indwelling catheter that has been in place for >2 weeks, consider catheter replacement before initiating antimicrobial therapy 3
• Monitor for clinical response within 48-72 hours
• A. urinae can occasionally cause serious complications such as bacteremia and endocarditis, particularly in elderly males with predisposing conditions 4

Common Pitfalls to Avoid

1. Using sulfonamides: A. urinae is typically resistant to sulfonamides, making trimethoprim-sulfamethoxazole potentially ineffective 4

2. Relying on fluoroquinolones as first-line therapy: Despite their broad spectrum, fluoroquinolones should be reserved for more severe infections due to increasing resistance and risk of collateral damage 3

3. Inadequate treatment duration: Too short a course may lead to treatment failure and recurrence

4. Failure to recognize the organism: A. urinae may be misidentified as alpha-hemolytic streptococci or staphylococci in routine cultures

5. Missing complicated infections: A. urinae can cause invasive infections, so patients with persistent symptoms despite appropriate therapy should be evaluated for complications

By following these recommendations, clinicians can effectively treat Aerococcus urinae UTIs even when antimicrobial susceptibility testing is not immediately available.