💉 Zycosan Vet Guide 2025 by Dr Duncan Houston

Welcome to this comprehensive veterinary guide on Zycosan® (pentosan polysulfate sodium), the first FDA-approved injectable for equine osteoarthritis. This article explains how it works, dosage, safety, side effects, monitoring, and practical clinical advice for treating arthritis in horses. 🐴✨

🔍 What Is Zycosan®?

Zycosan® is a sterile, clear IM solution containing **250 mg/mL pentosan polysulfate sodium**. It’s the first FDA-approved pentosan specifically indicated to **control clinical signs of osteoarthritis in horses**, including lameness, stiffness, and joint swelling :contentReference[oaicite:2]{index=2}.

🎯 How It Works

Though not fully understood, pentosan appears to stimulate **endogenous hyaluronic acid production** in joints—enhancing lubrication and shock absorption :contentReference[oaicite:3]{index=3}. It also has mild anticoagulant properties, offering secondary benefits but necessitating monitoring :contentReference[oaicite:4]{index=4}.

💊 Dosage & Treatment Protocol

• Route: Intramuscular (IM) injection only (neck muscle).
• Dosage: 3 mg/kg (≈1.4 mg/lb) once weekly for 4 weeks (total 4 doses) :contentReference[oaicite:5]{index=5}.
• Preparation: Single-use vial; no preservative—discard unused portion after each use :contentReference[oaicite:6]{index=6}.
• Onset: Most show measurable improvement around Day 28—one AAEP field study reported ~60% lameness score reduction and no significant adverse effects :contentReference[oaicite:7]{index=7}.

⚠️ Safety & Contraindications

Please observe caution in the following circumstances:

• **Bleeding disorders / Surgery**: Do not administer within 24 hours before or after surgery; it prolongs PT/aPTT :contentReference[oaicite:8]{index=8}.
• **Concurrent anticoagulants or NSAIDs**: Increased bleeding risk—monitor closely :contentReference[oaicite:9]{index=9}.
• **Hypersensitivity**: Avoid in horses allergic to pentosan or any inactive ingredients :contentReference[oaicite:10]{index=10}.
• **Undetermined safety**: Not evaluated in breeding, pregnant/lactating mares, or horses under 2 years old :contentReference[oaicite:11]{index=11}.
• **Food species restriction**: Not for horses intended for human consumption :contentReference[oaicite:12]{index=12}.

📈 Adverse Reactions & Monitoring

Field studies and commerical use report:

• **Injection-site reactions** (pain, heat, swelling up to 15 cm): seen in 15–18% of horses; commonly resolve within 5 days :contentReference[oaicite:13]{index=13}.
• **Prolonged clotting times** (PT/aPTT) in some—no clinical bleeding reported, but monitor if NSAIDs used :contentReference[oaicite:14]{index=14}.
• Less common: lethargy, colic signs, behavior changes, mild increases in SDH or liver enzymes :contentReference[oaicite:15]{index=15}.
• Occasional systemic effects—mild fever or discomfort resolved with NSAIDs :contentReference[oaicite:16]{index=16}.

🧪 Pre‑treatment and Ongoing Monitoring

• Obtain baseline CBC, chemistry (including SDH, enzymes), and clotting panel (PT/aPTT).
• During treatment: recheck PT/aPTT 24 hours post-injection; continue monitoring if on NSAIDs or post-surgery.
• Inspect injection site daily for swelling or heat—injection site reactions require no intervention unless severe.
• Observe for systemic signs—colic, lethargy, injection-site pain; treat with NSAID as needed.

📊 Quick Reference Table

✅ Clinical Tips from the Vet

• Ensure accurate weight-based dosing; use calibrated syringes.
• Rotate injection sites; use aseptic technique.
• Inform owners about possible swelling and systemic signs.
• Delay administration if surgery or NSAID therapy is planned—then monitor clotting daily.
• Plan booster treatments only after reevaluation and assessing joint response.

📲 Need Help?

For dosing calculators, monitoring templates, or client handouts on Zycosan®, contact our **Ask A Vet** team. Download the Ask A Vet app for 24/7 veterinary support, detailed protocols, and arthritis-care planning—all from your phone! 🌟