Macrobid (Nitrofurantoin) for Aerococcus urinae UTI
Nitrofurantoin is an effective and recommended treatment option for uncomplicated urinary tract infections caused by Aerococcus urinae, achieving clinical and microbiological cure rates of 71% and 76% respectively in the largest prospective treatment study. 1
Evidence Supporting Nitrofurantoin Use
Clinical Efficacy Data
A prospective observational study of 72 patients with aerococcal UTI demonstrated that nitrofurantoin achieved clinical success in 71% and microbiological success in 76% of A. urinae cystitis cases. 1
In vitro susceptibility testing shows 100% susceptibility of A. urinae isolates to nitrofurantoin, with excellent activity demonstrated across 166 clinical isolates. 2
Case reports and clinical experience support the use of penicillin, amoxicillin, and nitrofurantoin as appropriate treatment options for A. urinae infections. 3
Standard Dosing Regimen
For uncomplicated A. urinae cystitis, prescribe nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 5 days, following the same evidence-based regimen recommended for standard uncomplicated UTIs. 4, 5
Alternative formulations include nitrofurantoin macrocrystals 50-100 mg four times daily for 5 days. 4
The 5-day duration balances efficacy with minimizing antibiotic exposure and adverse effects. 5
Critical Limitations and Contraindications
When NOT to Use Nitrofurantoin
Do not use nitrofurantoin if pyelonephritis or upper tract involvement is suspected, as it does not achieve adequate renal tissue concentrations. 5
Avoid in patients with creatinine clearance below 30 mL/min due to increased risk of peripheral neuropathy and reduced efficacy. 5
Not appropriate for complicated UTIs with structural/functional abnormalities, obstruction, or indwelling catheters. 5
Important Clinical Distinction
Nitrofurantoin is significantly less effective for A. sanguinicola UTI (only 42% clinical success and 50% microbiological success), so species identification matters if treatment fails. 1 If A. sanguinicola is identified or suspected based on treatment failure, consider alternative agents like penicillin or ampicillin, which show 100% susceptibility. 2
Alternative Treatment Options
Pivmecillinam achieved success in A. urinae cystitis cases and can be considered as an alternative first-line agent where available. 1
Ciprofloxacin was effective for pyelonephritis cases in the prospective study, though 10.9% of Aerococcus isolates show ciprofloxacin resistance. 1, 2
Penicillin and ampicillin maintain 100% susceptibility and are appropriate alternatives, particularly for complicated cases or treatment failures. 2
Common Pitfalls to Avoid
Do not assume treatment failure is due to antibiotic resistance without culture confirmation, as A. urinae shows excellent susceptibility to nitrofurantoin but the clinical cure rate is lower than for typical E. coli UTIs. 1
Ensure adequate hydration during treatment to prevent crystal formation. 5
Obtain urine culture with susceptibility testing in older adults with multimorbidity, chronic urinary retention, or indwelling catheters, as these patients are at higher risk for A. urinae infection and may require culture-directed therapy. 3
The most common side effects are nausea and headache (5.6-34% incidence), while serious pulmonary and hepatic toxicity are extremely rare (0.001% and 0.0003% respectively). 5