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

Rush immunotherapy (RIT) accelerates the induction phase of allergen-specific immunotherapy treatment (ASIT) by administering incrementally increasing allergen doses over a single day. This approach reduces the time required to maintenance dosing. Safety information in cats with atopic skin syndrome (FASS) remains limited.

The objective of the study was to evaluate the safety of RIT in cats with hypersensitivity disease compatible with FASS and to describe the frequency and nature of adverse events.

Forty-seven client-owned cats that underwent RIT.

A multicentre medical record review from 2019 to 2024 was performed to identify cats that met at least six of 10 criteria for non-flea-induced hypersensitivity dermatitis and were therefore considered consistent with a diagnosis of FASS. All included cats received documented flea prevention and underwent elimination diet trials. Data collected included signalment, medical history, concurrent medications, RIT protocol details, monitoring findings and follow-up communication. Adverse events (AEs) were recorded.

In three of 47 cats (6.4%), AEs were observed including tachypnoea, behavioural distress and increased pruritus. In one cat, RIT was discontinued before protocol completion. All affected cats transitioned to maintenance ASIT without recurrence of AEs.

Rush immunotherapy appears to be safe in cats with FASS when performed with clinical monitoring. Adverse events were infrequent, mild and self-limiting, supporting use of accelerated induction protocols in appropriately selected patients.