From the Journals

Original Study: Should Nitrofurantoin Be Used to Treat Alkaline Urinary Tract Infection?

Emergency Medicine. 2018 July;50(7):142-144 | 10.12788/emed.2018.0099

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Results

Data were categorized into 16 different bacterial genera or species. Acinetobacter (n = 1), Kluyvera ascorbata (n = 2), and Stenotrophomonas maltophilia (n = 3) were underrepresented in the dataset and therefore were not included in the data analysis. The data are summarized in the Table.

Table.

In our dataset, the most common bacteria associated with UTI, irrespective of urine pH, were Escherichia coli (n = 818/1,331; 62%), Klebsiella (n = 167/1,331; 13%), and P mirabilis (n = 88/1,331; 7%). The mean urine pH in our cohort was 6.1 (range, 5.0-9.0; SD, 0.88; median, 6; and mode, 6), and 1,194/1,331 (90%) of all urine samples had a urine pH of 5.0 to 7.0. Among patients who had a urine pH of 7.5 to 9.0, E coli was the cause of UTI in 39% (53/137) and P mirabilis was the cause of UTI in 28% (38/137). Likewise, among patients who had a urine pH of 8.0 to 9.0, E coli was the cause of UTI in 36% (30/83), and P mirabilis was the cause of UTI in 31% (26/83). Lastly, in patients who had a urine pH of 8.5 to 9.0, P mirabilis was the most common cause of UTI, present in 35% (9/26) patients.

The mean urine pH in our dataset for P mirabilis (n = 88) was 7.0, with a standard deviation (SD) of 1.03 and the standard error of the mean (SEM) of 0.11. The majority, 50/88 (57%) of P mirabilis UTIs were associated with a urine pH of 5.0 to 7.0. However, the urine pH for P mirabilis was significantly more alkaline than the combined urine pH from all of the other bacterial genera and species in our cohort (P < .0001). The mean urine pH in our cohort, excluding the P mirabilis data, was 6.01 with an SD of 0.828 and a SEM of 0.023.

Limitations

Our data were obtained retrospectively from a single ED, and did not include the following information: patient age and gender, and mode in which urine samples were obtained (eg, Foley catheter, clean catch). In addition, no reports were available regarding the sensitivity of the urine cultures with respect to urine pH.

Discussion

While alkaline urine was present in only 10% of patients, a high percentage of alkaline UTIs were associated with P mirabilis, an organism with intrinsic resistance to nitrofurantoin. Therefore, health care providers could consider obtaining a urine culture and/or prescribing an antibiotic other than nitrofurantoin for treating uncomplicated UTIs with alkaline urine. In addition, nitrofurantoin has been shown to be less effective against otherwise susceptible organisms in an alkaline urine.⁹

Conclusion

Our data demonstrates that urine pH of UTIs diagnosed in ED patients varied with the associated bacterial pathogen, and thus urine pH potentially could affect ED provider choice of antibiotics for the treatment of UTIs. Additional research is needed to confirm our results from a larger, more diverse dataset before changes in practice are recommended.