Is Macrobid (nitrofurantoin) effective for treating Proteus urinary tract infections (UTIs)?

Nitrofurantoin (Macrobid) Is Not Effective for Proteus UTIs

Nitrofurantoin (Macrobid) should not be used for treating urinary tract infections caused by Proteus species due to inherent resistance patterns and reduced efficacy in alkaline urine.

Why Nitrofurantoin Is Ineffective Against Proteus

• Proteus species are generally resistant to nitrofurantoin, making it an inappropriate choice for treating Proteus UTIs 1
• Proteus species produce urease, which increases urine pH (makes it more alkaline), further reducing nitrofurantoin's effectiveness 1
• Studies show that at urine pH 8-9 (typical with Proteus infections), nitrofurantoin sensitivity drops significantly to 66.1%, and at pH >9, it drops further to 54.6% 1
• Higher rates of treatment failure and relapses occur when nitrofurantoin is used against Proteus UTIs 2

Recommended Alternatives for Proteus UTIs

First-line options:

• Trimethoprim-sulfamethoxazole (TMP-SMX) if local resistance rates are below 20% 3
• Fluoroquinolones (such as ciprofloxacin) if local resistance rates are below 10% 3
• Amoxicillin plus an aminoglycoside or a second-generation cephalosporin plus an aminoglycoside for complicated Proteus UTIs 3

For complicated or resistant Proteus UTIs:

• Third-generation cephalosporins (intravenous) for more severe infections 3
• Fosfomycin may be effective against some Proteus strains 4

Clinical Decision-Making Algorithm for Suspected Proteus UTI

1. Suspect Proteus when:

   • Urine is alkaline (pH ≥8) 1
   • Patient has history of kidney stones 1
   • Previous cultures have grown Proteus species

2. Initial empiric treatment:

   • Choose TMP-SMX or fluoroquinolone based on local resistance patterns 3
   • Avoid nitrofurantoin due to intrinsic resistance 1

3. After culture results:

   • Adjust therapy based on susceptibility testing 3
   • Treat for 7-14 days for complicated UTIs 3
   • Treat for 3 days with appropriate oral agent for uncomplicated cystitis 3

Important Considerations

• Alkaline urine (pH ≥8) in the emergency department is a strong predictor of nitrofurantoin resistance and possible Proteus infection 1
• Nitrofurantoin has the lowest odds ratio (0.48) for effectiveness among common antibiotics when urine pH is 8-9, making it a poor choice 1
• Proteus species represented 24.4% of isolates at pH 8-9 and 40% at pH >9, highlighting the correlation between alkaline urine and Proteus infection 1
• Treatment failures with nitrofurantoin against Proteus are well-documented, with high percentages of relapses reported 2

Common Pitfalls to Avoid

• Don't prescribe nitrofurantoin empirically when alkaline urine is present, as this strongly suggests Proteus or other urease-producing organisms 1
• Don't continue nitrofurantoin once Proteus is identified in culture, even if in vitro testing suggests sensitivity 1, 2
• Don't use fluoroquinolones as first-line therapy unless other options are contraindicated, to prevent development of resistance 3, 5
• Don't treat for less than 7 days for complicated Proteus UTIs, as shorter durations may lead to treatment failure 3