Retrospective Review of Rush Allergen-Specific Immunotherapy Safety in Cats With Atopic Skin Syndrome.

Rush immunotherapy in cats with FASS is safe, with infrequent, mild, self-limiting adverse events occurring in only 6.4% of cases.

This retrospective, multicentre study evaluated the safety of rush immunotherapy (RIT) in cats diagnosed with feline atopic skin syndrome (FASS). RIT compresses the induction phase of allergen-specific immunotherapy (ASIT) by administering incrementally increasing allergen doses within a single day, thereby reducing time to maintenance dosing. Forty-seven client-owned cats meeting at least six of ten established criteria for non-flea-induced hypersensitivity dermatitis were included. All cats had documented flea prevention and had undergone elimination diet trials prior to enrollment. Medical records from 2019 to 2024 were reviewed for signalment, medical history, concurrent medications, RIT protocol details, monitoring parameters, and adverse event (AE) data. Adverse events occurred in three of 47 cats (6.4%), consisting of tachypnoea, behavioural distress, and increased pruritus. Only one cat required discontinuation of the RIT protocol before completion. Importantly, all three cats with AEs successfully transitioned to maintenance ASIT without recurrence of adverse reactions. The AEs observed were mild and self-limiting, requiring no significant medical intervention. These findings suggest that RIT is a safe and practical option for accelerating ASIT induction in cats with FASS when appropriate clinical monitoring is performed. The low AE rate compares favourably with reports in canine patients and supports broader clinical application of RIT in feline dermatology. Limitations include the retrospective design, relatively small sample size, and potential variability in protocols across centres. Prospective studies with standardised protocols and longer follow-up are warranted to further characterise efficacy and long-term safety.

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