Medical Management of Recurrent Urinary Tract Infection

Uncomplicated urinary tract infection (UTI) in dogs is common and estimated to occur in 14% of all dogs during their lifetime.¹ Although most UTIs occur as single episodes, recurrent UTI (ie, 3 or more infections within 12 months, 2 or more within 6 months²) is not uncommon. Because recurrent UTI frequently involves one or more bacterial organisms that are resistant to commonly used antibiotics and because extended treatment courses are frequently recommended, the infection is often difficult and expensive to eradicate.

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Spayed dogs are at increased risk for recurrent UTI, which may develop at any age. Typical presenting complaints include pollakiuria, stranguria, dysuria, hematuria, urine dribbling, and inappropriate urination indoors. However, some dogs may be asymptomatic.

Defense mechanisms of the urinary tract that aid in prevention of recurrent UTI include systemic immunocompetence, normal urogenital anatomy, appropriate micturition, urine composition, and urinary bladder mucosal barriers. In many patients with recurrent UTI, an alteration of one of these defense mechanisms is identified; however, in approximately 29%, no underlying cause is identified.³

A comprehensive diagnostic evaluation to investigate possible risk factors for development of recurrent UTI includes a complete physical examination, complete blood count, serum chemistry profile, urinalysis, quantitative urine culture, and urinary tract imaging. Imaging may include abdominal radiography and/or ultrasonography, contrast studies, and cystoscopy. In some patients, obtaining biopsy specimens of the bladder wall for histopathologic evaluation and culture is recommended.

Successful medical management of recurrent UTI revolves around complete resolution of any current infection with appropriate antimicrobial therapy, as well as identification and elimination of any underlying factors that may increase the patient’s risk for recurrence. Anatomic abnormalities that may contribute to increased frequency of recurrent infection include ectopic ureters with resultant urinary incontinence, pelvic bladder, vestibulovaginal stenosis, and recessed vulva.  Although the association between anatomic abnormalities and increased incidence of UTI has not been definitively proven in dogs, correction of anatomic abnormalities may be considered if treatment of recurrence is refractory to medical management.⁴ However, approximately one-third of patients with recurrent UTI have no identifiable underlying risk factors for recurrence. In these patients, treatment revolves around effective and appropriate antimicrobial therapy as well as adjunctive therapy with supplements that promote an inhospitable environment for urinary pathogens.

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Antimicrobial selection for treatment of infection in a patient with recurrent UTI should be based on the results of quantitative urine culture and susceptibility testing. In intact males, the prostate-blood barrier should be considered when selecting an appropriate antibiotic. While waiting for culture results, initial empirical antibiotics reaching therapeutic concentrations in the prostate to consider include fluoroquinolones and trimethoprim-sulfonamide. Recommended treatment duration is 4 to 6 weeks. Following cessation of antimicrobial therapy, complete resolution of infection should be confirmed by quantitative urine culture.

In addition to antibiotic therapy, other treatment measures can be considered:

• Methenamine is a urinary antiseptic that decomposes at an acidic pH of less than 5.5 to form formaldehyde and ammonia. Formaldehyde is bactericidal and ammonia inhibits bacterial colonization within the bladder. Urinary acidity may be attempted via co-administration of ascorbic acid (vitamin C) or ammonium chloride, though maintaining an acidic urine pH of < 5.5, which maximizes conversion of methenamine to formaldehyde, is difficult. Methenamine may be suitable for long-term prophylactic treatment of recurrent UTI; however, it is contraindicated in dogs with chronic kidney disease and is not recommended for use in cats. Routine monitoring for development of urolithiasis in patients may be warranted. The recommended dose of methenamine mandelate (Mandelamine) is 10-20 mg/kg twice daily.  The recommended dose of methenamine hippurate (Hiprex and Urex) is 500 mg/dog twice daily.

• In women, supplementation with cranberry can reduce the recurrence of UTI.⁵ Studies evaluating cranberry juice, capsules, and extract suggest a role in the prevention of UTIs in susceptible populations, but are lacking in veterinary literature. The two active components of cranberry inhibit adherence of uropathogenic Escherichia coli to the urothelium and may also displace preattached E coli.⁵ These active components include fructose and proanthocyanidin (PAC). PAC is the active ingredient in one cranberry extract product formulated specifically for dogs. Alternatively, over-the-counter dried cranberry extract supplements may be used, although efficacy is dose dependent. Clinical trials with standardized PACs are needed to determine appropriate dosing.

• In healthy female dogs, lactic acid-producing bacteria (eg, Enterococcus canintestini, Lactobacillus spp) have been isolated from the urogenital tract of spayed dogs.^6,7 Furthermore, lactic acid-producing bacteria isolated from the urogenital tract of healthy intact female dogs have been shown to inhibit growth of common uropathogens by promoting an acidic environment within the urogenital tract and competing for nutrients.⁷ Therefore, daily oral administration of Lactobacillus or Enterococcus spp may result in increased vaginal colonization of these bacteria and consequential inhibition of uropathogens, but further prospective, controlled studies are needed.⁶

Closing Thoughts

In conclusion, recurrent UTI in dogs is a well-recognized condition that is often difficult and expensive to manage. A thorough diagnostic investigation of underlying factors that may predispose a patient to recurrence of UTI is indicated; however, no underlying factors may be identified in one-third of patients.  In these patients, treatment with effective antibiotics for an appropriate duration remains the most effective method of management. Additional approaches, including methenamine, probiotics, and cranberry, may also be considered as complementary and adjunct treatment options for prevention of UTI; however, these strategies lack strong evidence to support their use as routine management options and should not be used as an alternative to appropriate antibiotic therapy.