Sporadic bacterial cystitis (SBC; also known as simple UTI) is caused by a temporary break in host defenses. Patients are typically presented with compatible lower urinary tract signs and respond quickly to appropriate therapy; clinical signs do not readily recur. Because most antimicrobials achieve high concentrations in urine, most cases of SBC are one-time infections that respond well to appropriate first-line therapy (Table). If the diagnosis of infection is accurate, treatment for SBC in dogs may be empiric and based on knowledge of the commonly isolated pathogens and their typical susceptibility to antimicrobials.1 This is not true for young to middle-aged cats, as those with clinical signs of lower urinary tract disease are unlikely to have SBC and more likely to have feline lower urinary tract disease/feline urological syndrome.
When choosing an antimicrobial, the pharmacokinetics and pharmacodynamics of the drug, potential adverse effects (for both patient and pet owner), ease of administration, and cost should be considered.
Urine concentrations of antimicrobials are more important than serum concentrations during treatment of sporadic UTIs. Urine concentrations generally exceed serum concentrations, as most antimicrobials are excreted in an active form in the urine. If the urine concentration is ≥4 times than the minimum inhibitory concentration for the duration of the dosage interval, it will most likely be effective (90%) for treatment of UTIs caused by that pathogen4; therefore, despite a susceptibility test result of resistant for amoxicillin for first-time SBC caused by Escherichia coli or Staphylococcus pseudintermedius in dogs or cats, extremely high urine concentrations make amoxicillin the first choice for therapy, and initial or empiric treatment with amoxicillin/clavulanic acid is not recommended.1-3
Because the clinical signs of SBC are related to inflammation, treatment with NSAIDs can be considered (caution is advised in cats), and antimicrobials can be started only if clinical signs persist or increase in severity. New recommendations are to administer antimicrobial therapy for only 3 to 5 days, despite label directions for longer treatment durations. If clinical signs resolve after short-term treatment, there is no need for additional urinalysis or urine culture.1