IMHA Toolkit

Clinical protocols & thrombosis prevention awareness

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Equine IMHA Dosage Calculator

Clinical Basis: Derived from equine-specific clinical consensus guidelines and large animal veterinary literature.

Equine 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

Weight Entry

1. Immunosuppressive Plan

Dexamethasone IV (Acute Stage)

0.1 - 0.2 mg/kg

Primary choice for acute stabilisation; horses cannot efficiently process oral prednisone.

Prednisolone Oral (Maintenance)

1.0 - 2.0 mg/kg

Transition path once stable and eating. Given PO once daily (q24h).

⚠️ CRITICAL SAFETY WATCH: High-dose corticosteroids carry a documented risk of triggering Laminitis (Founder) in horses. Assess digital pulses and hoof temperatures every 12 hours. Cryotherapy should be ready.

📋 Equine Single vs. Dual Therapy Advisor

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

Active Intravascular Haemolysis (pink plasma / dark red urine) Sudden, Severe PCV Drop (>50% decrease within 24 hours) Profound, Persistent Auto-Agglutination (after saline checks) Severe Tissue Hypoxia (recumbency, severe tachypnoea, PCV < 12%)

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

2. Thrombosis Prevention

Critical Priority

Unfractionated Heparin (UFH)

40 - 100 U/kg SC

Traditional therapy. Given SC every 8 to 12 hours. Target parameters should be monitored using real-time aPTT labs where available.

LMWH (Dalteparin)

50 U/kg SC

Standard dosage: 50 U/kg subcutaneously once daily (q24h). Offers more predictable antithrombotic response profile.

Aspirin Maintenance

4 - 10 mg/kg PO

Alternate-day maintenance protocol targeting platelet COX-1 inhibition. Given PO every 48 hours.

⚠️ Prescribing Rule (Heparin Monotherapy Standard) Veterinarians should prescribe **EITHER** Unfractionated Heparin (UFH) **OR** LMWH (Dalteparin) alone. Do not combine heparin classes. Use caution when adding oral antiplatelet therapy like Aspirin due to bleeding/ulceration risks in stressed or steroid-treated horses.

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Thrombosis is a Primary Cause of Mortality. Equine IMHA patients enter a severely hypercoagulable state quickly. Antithrombotic therapy should be considered early, in line with current consensus guidance and the attending veterinary surgeon’s assessment to optimiSe survival chances.

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

📋 Equine Diagnostic & Clinical Guidelines

🔍 True Auto-Agglutination vs. Rouleaux

Equine blood naturally forms prominent **Rouleaux** (stacked coins aggregation), easily mimicking auto-agglutination. You **must** perform a Saline Dilution Test using 1 part blood to 4 or 10 parts saline. Normal rouleaux stacks dissolve instantly, whereas true diagnostic auto-agglutination persists.

🐴 Neonatal Isoerythrolysis (NI) Checks

In newborn foals presenting with acute haemolytic icterus in the first 24-36 hours postpartum, suspect NI. Instantly deny access to maternal colostrum. Support with alternative colostrum or washed maternal RBCs if blood count drops dangerously.

🔬 Detailed Neonatal Isoerythrolysis (NI) Diagnostic Guidance ▼

The Pathophysiology of NI: Neonatal Isoerythrolysis is an immune-mediated haemolytic anaemia that occurs when a newborn foal inherits red blood cell antigens from its sire that are different from those of its dam. If the dam was sensitised during pregnancy or previous births, her colostrum will contain high titres of antibodies targeting the foal's erythrocytes, causing rapid intravascular and extravascular haemolysis once consumed.

Vigilant Colostrum Screening & Timing: Clinical symptoms typically manifest within the first 12 to 36 hours of life. If NI is suspected, muzzle the foal immediately to deny further access to maternal colostrum. Screen the foal's blood and test the dam's colostrum against the foal's red blood cells (such as via crossmatch or a lytic test) to verify active antibody matching. Provide an alternative source of secure, tested colostrum, and prepare for washed maternal erythrocyte transfusions if packed cell volume falls critically.

📚 Clinical Decision Guide: Single vs. Dual Protocols ▼

The Equine Corticosteroid Standard: Dexamethasone (IV) is the standard first-line choice during the acute stage, as horses cannot convert oral prednisone efficiently in the liver. Once stable and eating, they can be transitioned to oral Prednisolone.

When to use Dual Therapy (from Day 1): Initiate dual protocols (such as adding supportive low-dose heparin alongside IV dexamethasone) immediately if the horse shows active intravascular haemolysis, severe hypoxia, or sudden catastrophic drops in PCV.

When to use Sequential Therapy: If the patient presents with stable extravascular IMHA, starting with standard corticosteroid monotherapy is highly acceptable. Perform continuous digital pulse assessments and maintain laminitis monitoring.

Mathematical Formulas (Proof)

Dexamethasone IV (Acute Stage): Weight (kg) × 0.1 mg to 0.2 mg/kg once daily (IV q24h)

Prednisolone Oral (Maintenance): Weight (kg) × 1.0 mg to 2.0 mg/kg once daily (PO q24h)

Unfractionated Heparin (UFH): Weight (kg) × 40 U to 100 U/kg subcutaneously (SC q8-12h)

LMWH (Dalteparin) Protocol: Weight (kg) × 50 U/kg subcutaneously once daily (SC q24h)

Aspirin Maintenance: Weight (kg) × 4 mg to 10 mg/kg orally every 48 hours (PO q48h)

Source: ACVIM Consensus Statements & Large Animal Medicine Guidelines. FORMULAE ARE SHOWN FOR TRANSPARENCY