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Alkaline Urine in the Emergency Department Predicts Nitrofurantoin Resistance
Johnathan M Sheele1, Claudia R Libertin2, Isaac Fink3
1Department of Emergency Medicine, Mayo Clinic, Jacksonville, Florida.
Background:
The Proteeae group (i.e., Proteus species, Morganella morganii, and Providencia species) frequently causes urinary tract infections (UTIs) and is generally resistant to nitrofurantoin. Proteeae species can produce urease, which can increase urine pH.
Objective:
Our aim was to determine whether higher urine pH in the emergency department is associated with nitrofurantoin resistance.
Methods:
A single health system database of emergency department patients aged 18 years and older who received urinalysis between April 18, 2014, and March 7, 2017, was examined using χ2 test and multivariable regression analysis.
Results:
Of 67,271 urine samples analyzed, 13,456 samples grew a single bacterial species. Urine cultures growing the Proteeae group were associated with significantly more alkaline urine than other bacteriuria cultures (odds ratio [OR] 2.20, 95% confidence interval [CI] 2.06-2.36; p < 0.001). The Proteeae species represented 4.4% of urine samples at pH 5-7, 24.4% at pH 8-9, and 40.0% at pH 9. At urine pH 5-7, 80.4% of urine samples were sensitive to nitrofurantoin; however, this percentage decreased to 66.1% for urine pH 8-9 and 54.6% for urine pH 9. Nitrofurantoin had the highest OR (2.10, 95% CI 1.85-2.39) among cefazolin, ciprofloxacin, and trimethoprim/sulfamethoxazole for bacteriuria sensitive to those antibiotics at urine pH 5-7. At urine pH 8-9 and 9, nitrofurantoin had the lowest OR among the antibiotics: 0.48 (95% CI 0.42-0.54) and 0.31 (95% CI 0.24-0.40), respectively (p < 0.001 for both).
Conclusions:
Urine pH of 8 or higher is associated with high rates of nitrofurantoin resistance.
Insights
Higher urine pH is linked to increased nitrofurantoin resistance in urinary tract infections caused by Proteeae species. This finding is crucial for guiding antibiotic selection in emergency departments.
Area of Science:
- Urology
- Infectious Diseases
- Clinical Microbiology
Background:
- The Proteeae group, including Proteus, Morganella morganii, and Providencia species, are common causes of urinary tract infections (UTIs).
- These bacteria are frequently resistant to nitrofurantoin and possess urease, an enzyme that elevates urine pH.
Purpose of the Study:
- To investigate the association between elevated urine pH in emergency department patients and the likelihood of nitrofurantoin resistance.
Main Methods:
- Analysis of a health system database of adult patients who underwent urinalysis between April 2014 and March 2017.
- Statistical methods included chi-squared test and multivariable regression analysis to assess the relationship between urine pH and bacterial resistance patterns.
Main Results:
- Urine cultures positive for Proteeae species showed significantly higher pH levels compared to other bacteriuria (OR 2.20).
- Proteeae prevalence increased with urine pH: 4.4% at pH 5-7, 24.4% at pH 8-9, and 40.0% at pH 9.
- Nitrofurantoin sensitivity decreased as urine pH rose, from 80.4% at pH 5-7 to 54.6% at pH 9. Nitrofurantoin exhibited the lowest odds of effectiveness at higher pH levels compared to other antibiotics.
Conclusions:
- Urine pH of 8 or higher is strongly associated with increased rates of nitrofurantoin resistance.
- These findings highlight the importance of considering urine pH when selecting antibiotics for UTIs, particularly in emergency settings.
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