IMHA Toolkit

Clinical protocols & thrombosis prevention awareness

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Feline IMHA Dosage Calculator

Clinical Basis: Derived from the 2019 ACVIM Consensus Guidelines for Cats and feline-specific literature.

Feline Standard Active

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Important Clinical Notice Calculations provided by the IMHA Toolkit are for academic review and clinical reference purposes only. All dosage values, clinical plans, and prescribing paths must be independently verified by the attending veterinary surgeon prior to administering treatment to any patient.

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Weight Parameters

Patient Weight Entry

1. Immunosuppressive Plan

Prednisolone Only

2 mg/kg/day

Suggested baseline: 2 mg/kg/day split twice daily (BID). Do not use prednisone.

Mycophenolate Mofetil

10 mg/kg BID

Dose target: 10 mg/kg twice daily (BID). Add for critical or poorly responsive patients.

🚨 FATAL TOXICITY WARNING: Never prescribe Azathioprine to cats. Felines are highly sensitive, and exposure causes rapid, catastrophic bone marrow suppression (myelosuppression) which is often fatal.

📋 ACVIM Single vs. Dual Therapy Advisor

Check presenting clinical signs to evaluate if dual protocol is indicated immediately:

Active Intravascular Haemolysis (pink plasma / dark red urine) Non-Regenerative Presentation (bone-marrow directed immune haemolysis) Profound, Persistent Auto-Agglutination Severe Tissue Hypoxia (multiple transfusions required or PCV < 15%)

Clinical Protocol Suggestion: Select presenting signs above to receive point-of-care recommendations.

2. Thrombosis Prevention

Critical Priority

Clopidogrel hydrogen sulfate

First-Choice / Flat Option

Recommended first-line standard. Many felines receive a standard flat dose of 18.75 mg/cat (1/4 tablet) once daily.

Rivaroxaban

0.5 mg/kg daily

Standard dosage: 0.5 mg/kg once daily. Directly blocks Factor Xa to combat hypercoagulable pathways.

⚠️ Prescribing Rule (Monotherapy Standard) Veterinary surgeons should prescribe **EITHER** Clopidogrel **OR** Rivaroxaban alone. Combining an antiplatelet with an anticoagulant significantly escalates the risk of gastrointestinal haemorrhage and internal bleeding, and should be reserved strictly for intensive care patients with active thromboemboli.

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Thrombosis is a Primary Cause of Mortality. Feline IMHA patients enter a severely hypercoagulable state quickly. Antithrombotic therapies should be initiated concurrently with the first corticosteroid dose to optimise survival chances.

⚠️ Please independently verify all calculated values before prescribing or administering medication.

📋 Feline Diagnostic & Clinical Guidelines

🔍 Spherocytes in Cats: Diagnostic Pitfalls

Unlike in dogs, true spherocytes are extremely difficult to identify in feline blood smears because normal feline red blood cells naturally lack prominent central pallor. Do not rely heavily on spherocytosis for diagnosing feline IMHA. Focus instead on auto-agglutination, Coombs' testing, and exclusion of secondary triggers.

🧪 Secondary Viral & Parasitic Screens

Most cases of feline IMHA are secondary to infectious agents or neoplasms. It is Recommended to run PCR/serology screens for **FeLV/FIV**, **Mycoplasma haemofelis** (Feline Infectious Anaemia), and *Cytauxzoon felis* before concluding that the disease is primary or autoimmune.

🔬 Recommended Pre-Corticosteroid Feline Screening Guidelines ▼

Checking for Mycoplasma haemofelis (PCR): Feline infectious anaemia is caused by haemotropic mycoplasmas that physically attach to the surface of erythrocytes, triggering immune-mediated clearance. Initiating high-dose immunosuppressive corticosteroids without active parasitic coverage can lead to severe systemic replication of the parasite. Running a PCR assay is highly sensitive and Recommended for all presenting cats.

Screening for Feline Leukaemia Virus (FeLV): Underlying retroviral infections are strong secondary triggers for haematologic immune-mediated diseases in cats. Screening via ELISA or PCR for FeLV and FIV must be performed prior to starting chronic steroid regimens, as profound immunosuppression can accelerate viral disease expression and lead to fatal aplastic or neoplastic complications.

📚 Clinical Decision Guide: Single vs. Dual Protocols ▼

The Feline Corticosteroid Standard: Prednisolone is the first-line foundation of therapy. Cats cannot convert Prednisone to active Prednisolone efficiently in the liver, meaning Prednisone should *never* be prescribed. Mycophenolate Mofetil (MMF) serves as a secondary agent with a delayed clinical onset of several days.

When to use Dual Therapy (from Day 1): Initiate dual protocols concurrent with prednisolone immediately if the cat shows signs of severe haemolytic disease, active intravascular haemolysis, severe non-regenerative anaemia, or profound auto-agglutination.

When to use Sequential Therapy: If the patient presents with stable, regenerative extravascular IMHA, starting with Prednisolone alone is standard. Add Mycophenolate or secondary agents (such as Chlorambucil/Cyclosporine) later if treatment fails (PCV drops after 5-7 days of steroids) or severe steroid intolerances appear.

Mathematical formulae

Immunosuppressant (Prednisolone): Weight (kg) × 2 mg/kg/day (Split BID is standard)

Secondary Agent (Mycophenolate): Weight (kg) × 10 mg/kg given twice daily (BID)

Platelet Inhibitor (Clopidogrel): Standard flat dose of 18.75 mg/cat once daily (Or alternate weight-based 2 mg/kg once daily)

Factor Xa Block (Rivaroxaban): Weight (kg) × 0.5 mg/kg given once daily

Source: Swann JW, et al. ACVIM Consensus Statement on treatment of IMHA in dogs and cats. JVIM 2019. FORMULAE ARE SHOWN FOR TRANSPARENCY