Comprehensive Vet Guide 2025: Zycosan® (Pentosan Polysulfate) for Horses 🐎💊

Written by Dr Duncan Houston, BVSc – trusted veterinarian & Ask A Vet founder 👨‍⚕️🐾

Zycosan® is the first FDA-approved injectable pentosan polysulfate sodium specifically for horses, aimed at relieving clinical signs of osteoarthritis—such as lameness, stiffness, and joint swelling. Approved in December 2022, it represents a major step forward in equine musculoskeletal care. 🐴📘

1. What Is Zycosan® & How It Works

Zycosan® delivers pentosan polysulfate sodium, a heparin-like compound administered via intramuscular injection. Though its exact mechanism isn’t fully understood, it’s believed to:

• Boost hyaluronic acid production for joint lubrication
• Reduce proteolytic enzymes and free radicals
• Inhibit inflammatory cytokines in arthritic joints

These combined effects help diminish inflammation and support joint mobility. :contentReference[oaicite:2]{index=2}

2. FDA Approval & Indications

On December 20, 2022, the FDA officially approved Zycosan® for the control of clinical signs related to equine osteoarthritis—a first-of-its-kind injectable pentosan polysulfate drug for horses. :contentReference[oaicite:3]{index=3}

The approval was based on a well-controlled field study where 57 % of treated horses improved by at least one AAEP lameness grade within 28 days, compared to 36 % in the placebo group. :contentReference[oaicite:4]{index=4}

3. Administration & Dosing

Zycosan® is administered intramuscularly at:

• 3 mg/kg (≈1.4 mg/lb)
• Once weekly, for a total of four doses over 28 days
• Single-use vials (7.5 mL) – discard any leftovers

Strict adherence to dosing is crucial for safe and effective treatment. :contentReference[oaicite:5]{index=5}

4. When Effects Begin

Improvement in lameness, stiffness, and range of motion often occurs within the 28-day course. Effects may begin sooner, but full results generally surface by the end of therapy. :contentReference[oaicite:6]{index=6}

5. Side Effects & Safety Considerations

Though generally well-tolerated, Zycosan® may cause:

• Injection-site reactions (heat, swelling, pain): ∼18 % immediate, ∼11 % delayed—usually resolving in 5 days without treatment :contentReference[oaicite:7]{index=7}
• Bleeding/coagulation changes: ~15 % had prolonged aPTT, ~4 % prolonged PT—no clinical bleeding noted :contentReference[oaicite:8]{index=8}
• Systemic effects: lethargy, behavior changes (~12 % and ~8 %), colic (~2 %), mild enzyme changes, stiffness (~1 %) :contentReference[oaicite:9]{index=9}
• Rare serious: severe injection-site swelling and colic needed NSAID/antibiotic treatment; resolved within days :contentReference[oaicite:10]{index=10}

6. Contraindications & Use in Specific Situations

Zycosan® should not be used in:

• Horses with bleeding or clotting disorders
• Horses on anticoagulants or NSAIDs within 24 hrs before or after injection :contentReference[oaicite:11]{index=11}
• Horses <2 years old, pregnant, lactating, or breeding—safety not evaluated :contentReference[oaicite:12]{index=12}
• Food animals—Zycosan® is for non-food horses only :contentReference[oaicite:13]{index=13}

7. Drug Interactions & Cautions

Caution is advised when Zycosan® is used with other medications:

• NSAIDs: additive anticoagulant effect—monitor for bleeding signs :contentReference[oaicite:14]{index=14}
• Anticoagulants: Zycosan itself is weakly anticoagulant—avoid combination :contentReference[oaicite:15]{index=15}

8. Long-Term Use & Repeat Courses

Long-term safety beyond the initial 4-week course hasn’t been thoroughly studied. Some veterinarians repeat therapy up to three times yearly (every 4 months), but this should be discussed with your vet. :contentReference[oaicite:16]{index=16}

9. Monitoring & Follow-Up

Your vet should monitor:

• Dose compliance and timing
• Signs of injection-site or systemic reactions
• Coagulation parameters (PT/aPTT) before repeat doses or if bleeding signs appear
• Clinical lameness improvement using AAEP grading tools

10. Role of Ask A Vet, Woopf & Purrz

• Ask A Vet: Advice on dosing schedules, handling side effects, and deciding on repeat therapy
• Woopf: Injection reminders, symptom logs, alerts for bleeding or GI signs
• Purrz: Track lameness scoring, behavior changes, injection-site reactions—shareable with vet

11. Real‑World Case Examples

Veterinarians have successfully used Zycosan® to reduce lameness and improve joint comfort in horses unresponsive to NSAIDs alone. Most cases show improvement by Day 28, with side effects being mild or absent.

12. FAQs

🐾 Can Zycosan® be repeated more often?

Guidelines suggest possible repeat course every 4 months, but long-term safety is untested—consult your vet for personalized protocol.

🐾 What if the horse undergoes surgery?

Avoid Zycosan® within 24 hours before or after surgical procedures to minimize bleeding risk. Monitor forging signs post-op.

🐾 Can Zycosan® cause colic?

Rarely (~2 %). If colic signs occur, veterinary evaluation is needed to treat promptly.

🐾 What if I miss a dose?

Administer as soon as possible, then continue weekly schedule. Don’t double-dose.

13. Summary Table

14. Final Thoughts from Dr Duncan

Zycosan® marks a veterinary milestone as an FDA‑approved, injectable therapy for equine arthritis. With correct dosing, vet oversight, smart monitoring, and tools like Ask A Vet, Woopf & Purrz, most horses enjoy better mobility and comfort. As with all medical treatments, outcomes are optimized through individualized care and vigilance. 🐎❤️

For injection assistance, lameness tracking, or repeat-therapy planning, visit AskAVet.com and download the Ask A Vet app. Your horse deserves a life of freedom and comfort—every hoofbeat counts. 🐴📱