What is the appropriate enrofloxacin dose in dogs versus cats and what adverse effects require monitoring?

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Enrofloxacin dosing differs fundamentally between dogs and cats, and exceeding 5 mg/kg/day in cats carries a risk of irreversible retinal degeneration and blindness. In dogs, enrofloxacin is administered orally at 5–20 mg/kg PO q24h (or divided q12h), with dose selection based on infection severity and pathogen susceptibility. Dogs receiving doses at the upper end of the range should be monitored closely for inappetence, depression, and vomiting.1 At 5 mg/kg/day in clinical field studies, only 2 of 270 dogs (0.7%) experienced drug-related side effects, both self-limiting vomition.1 Post-approval reporting has identified additional rare adverse effects in dogs including diarrhea, elevated liver enzymes, ataxia, seizures, depression, and lethargy.1 In cats, the approved dose is strictly 5 mg/kg/day PO — administered either as a single daily dose or divided into two equal doses q12h — and this ceiling must not be exceeded. Treatment should continue at least 2–3 days beyond resolution of clinical signs, to a maximum of 30 days.13 No drug-related side effects were reported in 124 cats treated at 5 mg/kg/day for 10 days in clinical field studies.1 Retinal degeneration is the critical feline-specific toxicity and is dose-dependent. Post-approval reports in cats include mydriasis, retinal degeneration (manifesting as retinal atrophy, attenuated retinal vessels, and hyperreflective tapeta), and loss of vision.1 Mydriasis should be treated as a warning sign of impending or existing retinal changes.1 Acute diffuse retinal degeneration is a known dose-dependent adverse effect of enrofloxacin in cats.2 Additional feline adverse effects include vomiting, anorexia, elevated liver enzymes, diarrhea, ataxia, seizures, depression, lethargy, vocalization, and aggression.1 In cats with reduced kidney function, no dose adjustment or interval prolongation is indicated based on pharmacokinetic data after intravenous administration. Clearance of enrofloxacin is similar among cats with norm