Acute pyelonephritis in cats is frequently caused by Escherichia coli resistant to potentiated penicillins but has a better prognosis than other causes of acute kidney injury.

To describe the clinical findings, microbiological data, treatment, and outcome of a population of cats with suspected acute pyelonephritis (APN). 32 client-owned cats. Retrospective case series from 2 veterinary teaching hospitals between January 1, 2014, and December 31, 2020. Cats were included if they had a positive bacterial urine culture and a clinical diagnosis of acute kidney injury. Older female cats with underlying chronic kidney disease have a higher probability to develop bacterial culture-positive acute kidney injury or APN. Escherichia coli was the most commonly cultured bacterial species, and E coli isolates with susceptibility testing were resistant to amoxicillin-clavulanate but susceptible to fluoroquinolones or third-generation cephalosporins. Of the 20 cats with available follow-up information in the medical record, 14 were alive at 3 months after hospital discharge. Markers of renal function including creatinine (P = .008), BUN (P = .005), and phosphorus (P < .001) at the time of presentation were all higher in nonsurvivors compared with survivors. The survival rate with feline APN is higher than previous reports of acute kidney injury when all etiologies are considered. Nonsurvivors had more pronounced azotemia upon initial presentation. Amoxicillin-clavulanate was a poor empirical antimicrobial in this cohort based on the microbiological data.