Fluoroquinolones (FQs) have excellent spectrum of activity against common gram-negative uropathogens. FQs are lipophilic, low protein-binding drugs with extensive tissue distribution. Prostatic concentrations are greater than or equal to serum concentrations.10
FQs provide concentration-dependent bacterial killing as well as a postantibiotic effect. To minimize toxicity and maintain efficacy, q24h dosing is recommended.10 The pharmacodynamic parameter most predictive of clinical and bacteriologic efficacy is the ratio of the 24-hour area under the curve to the MIC.6
FQs should be reserved for treating resistant infections, pyelonephritis, or prostatitis. Clinical cure rates of 87% have been reported following short-duration (ie, 3 days) enrofloxacin therapy in dogs with UTIs.11 FQs as a first-line therapy for uncomplicated UTIs should be avoided to minimize future antimicrobial resistance, as FQs are a second-tier (ie, voluntary restricted use) antibiotic class.
Higher antimicrobial resistance rates of urinary isolates occur in dogs treated with FQs in the past 30 days (28% susceptible) than in those that have not received antimicrobial therapy in the past 30 days (77% susceptible) or dogs previously treated with amoxicillin–clavulanic acid (74% susceptible).12
Oral absorption is decreased in the presence of di- and trivalent cations (eg, magnesium, aluminum, calcium).10 To maintain oral absorption, FQs should not be administered at the same time as other medications containing cations (eg, sucralfate,13 antacids containing aluminum or magnesium, phosphate binders).
Oral ciprofloxacin absorption is variable in dogs. In severe cases, recurrent infections, or cases in which treatment failure is suspected, a veterinary-labeled FQ is recommended. If ciprofloxacin use is unavoidable, the recommended dosage is 20-25 mg/kg PO q24h. Breaking or crushing tablets can improve bioavailability.14
In cats, side effects can include dose-dependent retinal degeneration and blindness.15 Feline populations at highest risk are those treated with high doses or overdoses of FQs, rapid IV infusions, and prolonged therapy as well as those with decreased glomerular filtration rate (eg, cats with chronic kidney disease or dehydration, geriatric cats).16-18
The risk for retinal degeneration in cats varies with the type of FQ. For example, no retinal changes have been reported for marbofloxacin at 20 times the label dose and pradofloxacin at 10 times the label dose, whereas retinal degeneration has been reported for enrofloxacin at 4 times the label dose.16-18
In cats with severe azotemia, FQ dose adjustment should be considered. An empirical recommendation based on concentration-dependent bacterial killing of FQs includes prolonging the dosing interval from q24h to q48h.
FQs have been associated with articular cartilage erosions in growing animals, especially dogs. FQs are not approved for use in skeletally immature puppies. Due to central inhibition at the -aminobutyric acid receptor, FQs, especially enrofloxacin, should be avoided in patients with a history of seizures.19
FQs interfere with hepatic clearance of theophylline, resulting in a prolonged half-life and the potential for theophylline toxicity.20