Urinary tract infections (UTIs) are commonly seen in veterinary practice. While treatment in certain patient populations is straightforward, UTIs can become challenging to manage when there are concurrent complicating factors.
Uncomplicated UTI
With a typical UTI, a queen (of the appropriate age) or bitch urinates small amounts frequently, seems uncomfortable (often in general, but specifically while urinating), and there appears to be blood in the urine. While a culture is still recommended in these cases (due to the rising prevalence of resistant microbes in the environment), a penicillin (e.g., amoxicillin) is a good empiric choice as it concentrates in the urine. A sulfa antibiotic is another good option. Other antibiotics (e.g., enrofloxacin, nitrofurantoin) should be reserved for recurrent cases. As always, sample collection via cystocentesis is preferred.
Recurrent UTIs
Managing recurrent UTIs can be complicated, largely because of antibiotic resistance. The first step in treating a recurrence is to rule out or mitigate other causative factors. Imaging for uroliths is important, as these will be a source of recurrence because they release previously protected bacteria back into the bladder.
UTI in male cats and dogs
UTI is significantly less common in male dogs and cats than in females owing to the male anatomy. Urinary tract infections are much less common in toms and treatment reasonably straightforward, but in male dogs the frequency of prostatic involvement complicates treatment. Male dogs should be tested for prostatic involvement via abdominal ultrasound and/or aspiration of the prostate as warranted. If testing does not reveal prostatic involvement, then treating as an uncomplicated UTI is reasonable. There is a risk for recurrence, but current evidence does not support the use of longer courses of antibiotics to prevent this. If the prostate is involved, then a longer course of an antibiotic with better lipid solubility and thereby tissue penetration is recommended. The best evidence we have is for the use of fluoroquinolones for at least a month.3
Additionally, assessment of anatomy is important. Search for vulvar or ureteral abnormalities, both of which can contribute to UTI recurrence. In older patients, transitional cell carcinoma may predispose patients to recurrent UTI. Metabolic disease, such as unregulated diabetes or Cushing disease, may also be at play. Without control of these conditions, the risk for recurrence is much higher, and controlling these conditions may end the cycle of recurrence.
Once concomitant factors have been mitigated, culture-based treatment is still the appropriate course of action. A slightly longer course of treatment is recommended for patients with recurrent UTI (5-7 days as opposed to the standard 3-5 days.) Several other preventive measures have been discussed, but few have been proven efficacious.1 No positive effect was found with direct instillation of any substance into the urinary tract (antimicrobial or otherwise). Pulse antibiotic therapy is commonly used, but this practice is controversial as its effect is not fully clear and it may further increase the risk for developing resistance. Administration of probiotics was tested and not found to be particularly efficacious.
One recommendation that has been found to be effective (in humans at least) is administration of cranberry extract.1,2 There is also a fair amount of anecdotal evidence, in both veterinary and humane medicine, to suggest its utility. The proanthocyanidin in the cranberry inhibits uropathogenic Escherichia coli adherence to the urinary epithelium, preventing an infection recurrence.2
Other complicating factors
Subclinical bacteria
Another clinical complication of recurrent UTIs is the presence of subclinical bacteria, in which a patient’s urinary sediment is quiescent and there are no clinical signs of cystitis but the urine culture tests positive. There is strong evidence in human medicine that no treatment is warranted in these cases.3 Some exceptions include patients who are set to undergo any procedure in which bacteremia may be induced (e.g., urinary surgery in which hemorrhage may expose the blood stream to urine).
Pyelonephritis
Finally, a more life-threatening complication of UTIs is pyelonephritis. Patients with this condition present with acute onset of systemic signs (e.g., lethargy, anorexia, vomiting) and are found to have new-onset azotemia. Direct diagnosis requires pyelocentesis (aspiration of the renal pelvis), but this is not commonly performed due to difficulty in performing this procedure. In a patient with new-onset azotemia who is clinically ill and has no toxin exposure consistent with the azotemia, pyelonephritis is largely assumed and treatment (antibiotics) is initiated. This assumption is made in large part because pyelonephritis is the most treatable cause of acute kidney injury. (Keep in mind that this patient population completely overlaps with those suffering from leptospirosis, so appropriate testing and staff safeguards are important until this is ruled out.)
On ultrasound, pyelectasia (dilation of the renal pelvis) is suggestive of but not definitive for pyelonephritis. Ultrasound also helps to rule out other causes of acute kidney injury, such as obstructive ureteroliths, neoplasia, or ischemia. Patients with these conditions require hospitalization and varying levels of fluids and other supportive care. Antibiotic selection should be based on culture, but initial empiric treatment is important. Most commonly, a potentiated penicillin (ampicillin-sulbactam) with a fluoroquinolone is recommended. This is both for broad-spectrum coverage as well as good tissue penetration into the renal tissues with the fluoroquinolone. Prognosis in these cases is fair, although there will be some degree of permanent renal compromise that is not predictable at the outset.
Final thoughts
UTIs are common, but complications are rare. Appropriate urine culture is the bedrock on which treatment should be based, both for best patient outcome and antibiotic stewardship. While not mentioned above, contacting a veterinary microbiologist can also be helpful in guiding antibiotic recommendations.
A board-certified criticalist at Mount Laurel Animal Hospital in Mount Laurel, NJ, Dr. Greenway earned his DVM from Texas A&M University and is a proud member of the American College of Veterinary Emergency and Critical Care. He was truly inspired by his father, a military veteran, who fostered a deep commitment to animals. His professional interests include emergency (polytrauma, severe anemia) and critical care (septic case management).
References
- Dorsch R, Teichmann-Knorrn S, Sjetne Lund H. Urinary tract infection and subclinical bacteriuria in cats: A clinical update. J Feline Med Surg. 2019;21(11):1023-1038. doi: 10.1177/1098612X19880435
- Sihra N, Goodman A, Zakri R, Sahai A, Malde S. Nonantibiotic prevention and management of recurrent urinary tract infection. Nat Rev Urol. 2018;15(12):750-776. doi:10.1038/s41585-018-0106-x
- Weese JS, Blondeau J, Booth 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. Vet J. 2019;5:8-25.doi: 10.1016/j.tvjl.2019.02.008
