Updates in management of urinary tract infections in small animal medicine

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Antimicrobial stewardship is a major topic in both veterinary and human medicine. Recommendations for treatment of common types of infections have changed as new data become available. During a session at the 2024 dvm360 Fetch Coastal conference in Atlantic City, Mark Acierno, DVM, MBA, DACVIM, professor and associate dean at Midwestern University College of Veterinary Medicine in Glendale, Arizona, discussed updated recommendations for managing urinary tract infections (UTIs) in dogs and cats.¹

New definitions

Although urine was once thought to be sterile, new analyses have found numerous bacterial and fungal species exist in both human and animal urine. This has led to new definitions, which “are important due to good antimicrobial stewardship,” Acierno said, including the following:

• Bacteriuria: presence of bacteria in the urine
• Subclinical bacteriuria: bacteriuria in the absence of clinical signs of UTI
• UTI or bacterial cystitis: bacteriuria in the presence of clinical signs, including hematuria, pollakiuria, stranguria, and/or dysuria

“Treatment of subclinical bacteriuria is not indicated for humans, dogs, or cats,” Acierno said. Up to 12% of healthy dogs and 13% of healthy cats have subclinical bacteriuria.² Even if pyuria is present along with bacteriuria, antibiotic therapy is not recommended in the absence of clinical signs of cystitis.

In veterinary medicine, UTIs occur more commonly in female dogs compared to males because of differences in anatomy. “Cats rarely have UTIs because of their cleanliness and [high] osmolarity,” Acierno said, noting that the vast majority (>95%) of cats with feline lower urinary tract disease (FLUTD) do not have bacterial cystitis. Further workup and culture are always indicated in cases of feline UTIs.

Management of sporadic UTIs

Sporadic UTIs occur less than 3 times in 1 year or less than 2 times in a 6-month period. Ideally, urine cultures should be performed, though empirical treatment is reasonable in these cases. Nonsteroidal Anti-inflammatory Drugs (NSAIDs) can help to decrease clinical signs of cystitis pending culture results.

Amoxicillin, amoxicillin and clavulanate potassium (Clavamox; Zoetis), and trimethoprim and sulfamethoxazole (Tribrissen [TMS]; Jurox) for 3 to 5 days are the top empirical recommendations because they concentrate well in the urine.² Acierno acknowledged that many veterinarians are nervous to use TMS because of known adverse effects such as keratoconjunctivitis. However, these adverse effects are rarely seen with such a short course of medication.

Rechecking patients with sporadic UTIs is not indicated unless clinical signs do not resolve. This includes rechecking urinalysis and culture.

Management of recurrent UTIs

A UTI is considered recurrent when it occurs more than 3 times in 1 year or more than twice in a 6-month period. Recurrence can occur for 3 reasons:

• Relapse, due to the presence of a bacterial reservoir in the body
• Reinfection, which often occurs in the presence of immunosuppression
• Refractory, which may be due to poor medication compliance or the presence of a biofilm that protects microorganisms.

Recurrent UTIs require further workup to determine the reason for recurrence and best treatment plan. First, a thorough physical examination that includes direct observation of the patient’s urination and conformation of external genitalia. A common cause for recurrent UTIs is hooded vulvas, which respond well to surgical correction. Acierno recommended checking the fur around the vulva for urinary staining, which can indicate urine is being trapped.

Next, other underlying conditions, such as endocrine disease, should be ruled out with lab work, including a complete blood count, chemistry panel, and urinalysis. Culture and sensitivity on a sample obtained by cystocentesis is indicated in cases of recurrent UTIs.

Imaging is performed to assess for stones, neoplasia, and other anatomical abnormalities in the lower urinary tract. Radiographs can be used, but even a boarded radiologist will miss as many as 27% of uroliths. Ultrasound is preferred as it has a lower false negative rate of only 6%.¹ The final step in the workup of recurrent UTIs is cystoscopy, according to Acierno’s presentation.

Once treatment is started based on results of culture and sensitivity, a culture should be obtained 1 week into treatment to confirm efficacy. As long as this culture is negative, treatment should be continued for a total of 4 weeks. An additional culture should be obtained 1 week after treatment to ensure full resolution.

Acierno noted that there are many adjunctive treatment options that have been proposed for these cases, such as probiotics or cranberry extracts, though evidence for their use in dogs is low. New therapies are under investigation.

Considerations for male dogs

Acierno noted that although UTIs are much less common in male dogs, it is important to assess the prostate for intact males with UTIs. This is best done by ultrasound. Cytology and culture of the prostatic fluid is ideal, but culture samples should be submitted as tissue samples to get accurate results. When the prostate is involved, treatment is needed for 4 to 6 weeks. fluoroquinolones, TMS, and macrolides are preferred due to excellent tissue penetration.

Takeaways

Although urine was once thought to be sterile, new data show that some animals have normal bacterial flora in their urine. This changes how the presence of bacteriuria should be interpreted and treated. Only patients with bacteriuria and clinical signs of urinary tract infection should be treated with antibiotics. While culture is ideal, empirical treatment is appropriate in cases of sporadic UTIs. Recurrent UTIs require further evaluation and longer treatment courses.

Kate Boatright, VMD, is a 2013 graduate of the University of Pennsylvania, a practicing veterinarian, a freelance speaker and an author, based in western Pennsylvania. She is passionate about mentorship, spectrum of care, education, and addressing common sources of stress for veterinary teams and recent graduates. Outside of clinical practice, Boatright is actively involved in organized veterinary medicine at the state and national levels.

References

1. Acierno M. Making sense of the new UTI antimicrobial recommendations. Presented at Fetch Coastal 2024: Atlantic City, NJ. October 13, 2024.
2. Weese JS, Blondeau J, Boothe D, et al. International society for companion animal infectious diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats. The Veterinary Journal. 2019;247:8-25. doi:10.1016/j.tvjl.2019.02.008. https://www.sciencedirect.com/science/article/pii/S109002331830460X?via%3Dihub