what immunosuppressive protocols are recommended for immune-mediated thrombocytopenia in cats?

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Accepted Answer

Glucocorticoids are the first-line immunosuppressive treatment for feline immune-mediated thrombocytopenia (ITP), with additional agents selected based on treatment response. Azathioprine is absolutely contraindicated in cats and must never be used — it causes fatal myelosuppression in this species.2 Immunosuppressive glucocorticoids form the foundation of feline ITP treatment. The 2024 ACVIM Consensus Statement on the Treatment of ITP in Dogs and Cats identifies glucocorticoids at immunosuppressive doses as first-line therapy for both species.2 The specific feline dosing protocol is not detailed in the consensus abstract, but glucocorticoid monotherapy carries a meaningful relapse risk — in the published feline case, relapse occurred within 3 weeks of initiating glucocorticoid treatment.1 When glucocorticoids fail or relapse occurs, second-line immunosuppressive agents are added. The 2024 ACVIM consensus identifies modified cyclosporine and mycophenolate mofetil (MMF) as the appropriate second-line options in cats.2 Azathioprine, while listed as a second-line agent in dogs, is contraindicated in cats due to fatal myelosuppression and is explicitly excluded from feline protocols.2 Chlorambucil has been used in at least one refractory feline ITP case, though its efficacy was insufficient as a single agent in that patient.1 MMF has documented use in refractory feline ITP. In the published case of a British Shorthair cat with primary ITP refractory to glucocorticoids and chlorambucil, MMF was used successfully following splenectomy and achieved remission sustained over 6 months.1 Specific feline MMF dosing for ITP is not established in the available literature. Vincristine and human IV immunoglobulin (hIVIg) are adjunctive options for severe or refractory cases. Both are identified in the ACVIM consensus as part of the feline ITP treatment armamentarium, typically reserved for more severe presentations.2 Vincristine at 0.02 mg/kg IV is associated with faster platelet c