Hyaluronic acid (HA), also known as sodium hyaluronate, is a naturally occurring glycosaminoglycan that is a major component of synovial fluid and articular cartilage. In equine medicine, exogenous HA is administered by intra-articular (IA) or intravenous (IV) injection to treat joint inflammation and support joint health. Legend (Bayer/Elanco) is the most recognized FDA-approved brand for IV use in horses, while several HA products are available for intra-articular administration.
Overview
Hyaluronic acid serves multiple functions in the joint: it provides viscoelasticity to synovial fluid, acts as a lubricant, supports nutrient transport to articular cartilage, and has anti-inflammatory properties. In diseased joints, HA concentration and molecular weight are reduced, contributing to poor lubrication and increased inflammation. Exogenous HA supplementation aims to restore synovial fluid quality, reduce inflammation, and slow cartilage degradation. HA has been shown to inhibit prostaglandin E2 production, reduce inflammatory cell migration, and scavenge free radicals within the joint.
Uses
- Synovitis — joint membrane inflammation; FDA-approved indication for Legend (IV)
- Osteoarthritis / Degenerative joint disease — widely used in performance and aging horses
- Post-arthroscopic surgery — IA injection to support joint recovery
- Acute traumatic joint injury — to reduce inflammatory response
- Multimodal joint therapy — combined with corticosteroids (triamcinolone) or PSGAG (Adequan) for enhanced benefit
- Preventive joint support — some veterinarians use periodic IV Legend for high-performance horses
Dosage
Administered by a veterinarian only.
| Route | Product | Dose | Frequency |
|---|---|---|---|
| Intravenous | Legend (IV) | 40 mg (4 mL) IV | Weekly for 3 treatments; may repeat as needed |
| Intra-articular | Various HA products | 10-20 mg per joint | As directed (often single injection per treatment cycle) |
IV administration (Legend): The labeled protocol is 40 mg IV once weekly for 3 weekly treatments. Many veterinarians administer periodic IV HA treatments (e.g., monthly or before competition seasons) for maintenance.
IA administration: Intra-articular HA is injected directly into the affected joint under strict aseptic technique. It is frequently combined with a corticosteroid such as triamcinolone acetonide for synergistic anti-inflammatory and chondroprotective effects.
Side Effects
| Common | Serious (Contact Your Vet) |
|---|---|
| Mild transient joint swelling after IA injection | Septic arthritis (joint infection from IA injection) |
| Brief increase in lameness post-IA (24-48 hours) | Severe joint flare (excessive inflammation post-injection) |
| Mild neck swelling at IV site (rare) | Anaphylaxis (extremely rare) |
Hyaluronic acid is generally very well tolerated by both IV and IA routes. The most significant risk is joint infection following intra-articular injection, which is a risk inherent to all IA procedures regardless of the drug used. Strict aseptic technique, including surgical preparation of the injection site, is essential.
Drug Interactions
- Intra-articular corticosteroids (triamcinolone, methylprednisolone): Commonly combined for enhanced joint therapy. No adverse interaction.
- PSGAG (Adequan): Often used in combination for multimodal joint management.
- NSAIDs: No significant interaction; commonly used concurrently for pain management.
- Do not mix HA with quaternary ammonium disinfectants in the same syringe, as they degrade HA.
Contraindications
- Active septic arthritis (do not inject into an infected joint)
- Known hypersensitivity to hyaluronic acid or avian-derived products (some HA products are derived from rooster combs)
- Skin infection or wound at the proposed injection site (IA use)
- Coagulopathy at IA injection site
Storage
- Store at controlled room temperature, 59-86 degrees F (15-30 degrees C).
- Do not freeze.
- Protect from light.
- Use single-dose vials/syringes promptly; do not store opened product.
Frequently Asked Questions
How long do the effects of a joint injection with HA last? The duration varies by horse and joint. Many horses show improvement for 2-6 months after IA injection. Some require periodic re-treatment. The combination of HA with triamcinolone often provides longer-lasting benefit than either alone.
Is IV Legend as effective as intra-articular HA? They work differently. IV Legend provides systemic HA that reaches multiple joints and is useful for generalized joint support. IA injection delivers a concentrated dose directly to the affected joint. Your veterinarian will recommend the best approach for your horse’s condition.
Can I give oral hyaluronic acid supplements instead? Oral HA supplements are widely available but have limited scientific evidence supporting their efficacy compared to injectable HA. The bioavailability of oral HA in horses is uncertain. Discuss supplement use with your veterinarian.
Is HA allowed in competition horses? HA regulations vary by governing body and competition level. IV Legend and IA HA are generally permitted but may have withdrawal time requirements. Check your specific competition rules.
This information is for educational purposes only and does not replace professional veterinary advice. Always consult your veterinarian before administering any medication to your horse.