Alfaxalone is a synthetic steroid anesthetic used for induction and maintenance of anesthesia. Neurosteroid GABAA anesthetics reportedly have a wide therapeutic range and high therapeutic index (>30 mg/kg) in cats; however, the exact therapeutic index for alfaxalone use in cats has not yet been established. A 12-year-old cat was anesthetized for MRI using alfaxalone and maintained via continuous-rate infusion. The intended dose was 0.1 mg/kg/min; however, because of a calculation error, the cat received 1 mg/kg/min. When the cat’s anesthetic plane was determined to be too deep (after >105 minutes), alfaxalone was discontinued and anesthesia maintained with isoflurane alone for the next 45 minutes. On extubation, the cat was transferred to an intensive care unit. Supplemental oxygen, IV crystalloid fluids, and rewarming care were provided. The cat had a prolonged recovery and was alert, active, and responsive ≈11 hours postextubation. The cat was discharged ≈24 hours postextubation.