Pyelonephritis in Small Animals

Escherichia coli is the organism most commonly cultured from dogs and cats with pyelonephritis.

Pyelonephritis is an important cause of acute-on-chronic kidney disease. Pyonephrosis (accumulation of purulent material in the renal pelvis secondary to an obstruction) is a complication that may develop and typically requires emergent intervention.

Pyelonephritis can occur in a dog or cat of any signalment; however, more patients are female and older.

Pyelonephritis can be acute and cause acute kidney injury or can be chronic and result in relapse infections.

Clinical signs (lethargy, inappetence, vomiting, diarrhea) of pyelonephritis can be associated with systemic illness from the acute kidney injury or related to cystitis. Fever and abdominal pain can occur but are uncommon in both dogs and cats. Neutrophilia with a left shift can be supporting evidence for pyelonephritis but does not consistently occur.

A presumptive diagnosis of pyelonephritis is made in a patient with acute kidney injury and positive results of culture from urine collected by cystocentesis.

Some cats undergoing placement of a subcutaneous ureteral bypass device have bacterial growth from the upper urinary tract but not the lower. Therefore, a definitive diagnosis of pyelonephritis is made from positive results of urine culture collected by pyelocentesis. However, not all studies support the need for culture to be performed from this location.

Patients should undergo a through diagnostic evaluation to investigate for comorbidities and to rule out other causes of acute kidney injury.

Antimicrobial treatment of pyelonephritis should be based on urine culture and susceptibility results. The overall prevalence of pyelonephritis as a cause of acute kidney injury is relatively low; therefore, empirical use of antimicrobials while urine culture is pending should only be initiated in cases with a high clinical suspicion for this disease, such as bacteriuria on urine sediment examination.

Pyelonephritis is a tissue infection; consequently, it is important to inform the microbiology laboratory about this concern when submitting a urine culture so that plasma minimum inhibitory concentration breakpoints are used instead of urine breakpoints. This primarily applies to the penicillins. Clinicians should be aware that E coli is the most common organism that causes pyelonephritis and is usually resistant to penicillins based on plasma breakpoints. The same rationale could be applied to deep-seated infections of the urinary bladder.

A fluoroquinolone or third-generation cephalosporin would be a reasonable option for empirical use in most areas. Although pradofloxacin is convenient for administration to cats as an oral suspension, it should be reserved if a second-generation fluoroquinolone can be used instead.

Clinicians should be mindful of retinopathy as an adverse effect of fluoroquinolones in cats, especially with enrofloxacin compared to others in this class.

Historically, treatment duration of 4–6 weeks was recommended; however, the current recommendation is 10–14 days. This recommendation is extrapolated from findings in human medicine because evidence in small animals to guide appropriate duration of therapy does not exist. Consequently, clinicians should recheck the patient within 1–2 weeks after cessation of antimicrobial therapy to evaluate for evidence of ongoing kidney injury due to infection.

• International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats.

• Clinical and Laboratory Standards Institute veterinary antimicrobial susceptibility testing standard.