Comparing Injectable Therapies for Osteoarthritis in Dogs and Cats

Osteoarthritis (OA) is a complex, progressive condition that causes pain, stiffness, and reduced mobility in dogs and cats. Injectable therapies have become an essential part of multimodal management, offering targeted joint support when oral medications or lifestyle changes aren’t enough. With a growing number of options available, it’s important to understand how each therapy works, what evidence supports it, and when it may be most appropriate.

Polysulfated Glycosaminoglycans (Adequan®)

• Mechanism: Disease-modifying osteoarthritis drug (DMOAD) that supports cartilage metabolism, reduces inflammation, and improves synovial fluid quality.
• Use: Typically given as a series of intramuscular injections, with periodic booster series.
• Pros: Long track record, well tolerated, relatively affordable.
• Cons: Requires repeated series for sustained effect; not always sufficient in advanced cases.

Arthramid® (2.5% Polyacrylamide Hydrogel)

• Mechanism: Arthramid is a 2.5% cross-linked hydrogel injected intra-articularly. Over several weeks it integrates into the synovial membrane, improving elasticity, dampening inflammation, and restoring joint function. It becomes part of the synovium rather than just coating surfaces.
• Duration: Clinical effects typically last 12–18 months.
• Evidence: Backed by peer-reviewed studies in dogs, horses, and humans, with demonstrated efficacy and safety. In humans it is used as Bulkamid®, Aquamid®, and Arthrosamid®, providing a strong One Health foundation.
• Pros: Well-studied across species, disease-modifying potential, long duration of effect.
• Cons: Requires strict sterile injection; transient soreness possible; cost and availability may limit access.

Noltrex® Vet (4% Polyacrylamide Hydrogel)

• Mechanism: Noltrex is a higher-concentration hydrogel that does not integrate into tissue. Instead, it forms a protective, lubricating coating on cartilage surfaces, reducing friction and distributing load inside the joint.
• Duration: Effects typically last 6–12 months.
• Evidence: While widely used in equine practice, Noltrex currently lacks the robust peer-reviewed efficacy data in horses or humans that Arthramid has. Veterinary reports exist, but controlled studies are limited.
• Pros: Provides mechanical cushioning and friction reduction, especially useful in joints with cartilage wear. Expanding use in small animals.
• Cons: Less published scientific validation compared to Arthramid; shorter reported duration of effect.

Spryng™ with OsteoCushion Technology

• Mechanism: Veterinary medical device that apparently forms a cushioning matrix inside the joint. Designed to mimic cartilage’s shock absorption and lubrication properties.
• Use: Single intra-articular injection, primarily marketed for dogs.
• Pros: Provides immediate mechanical support, non-drug option.
• Cons: No evidence in any species to support its use.

Hyaluronic Acid (HA)

• Mechanism: Viscosupplementation that improves joint lubrication, reduces inflammation, and supports synovial fluid health.
• Use: Commonly injected intra-articularly in both humans and animals.
• Pros: Long history of use, can be combined with PRP or corticosteroids.
• Cons: Effects may be short-lived (weeks to months); less robust long-term efficacy data in veterinary medicine.

Synovetin OA® (Sn-117m Radiosynoviorthesis)

• Mechanism: Injectable radiotherapeutic that delivers localized, low-energy radiation to synovium, reducing inflammation at its source.
• Use: Single intra-articular injection with effects lasting 9–12 months or longer.
• Pros: Truly disease-modifying; no systemic drug exposure.
• Cons: Requires nuclear license and referral; not widely available.

Platelet-Rich Plasma (PRP) and Stem Cells

• PRP: Concentrates platelets and growth factors to promote healing, reduce inflammation, and stimulate tissue repair.
• Stem Cells: Mesenchymal stem cells from bone marrow or fat may provide regenerative, immunomodulatory effects.
• Pros: Autologous (patient’s own blood), biologically active, can be tailored to the patient.
• Cons: Variable quality depending on processing; cost; not always long-lasting.

Monoclonal Antibodies (Librela®, Solensia®)

• Mechanism: Target nerve growth factor (NGF) to reduce pain signaling.
• Use: Monthly injections for dogs (Librela) and cats (Solensia).
• Pros: One injection under the skin.
• Cons: It has not been studied in combination with NSAIDs, not for neurological disease, concerns over cumulative half-life and potential adverse events. I only use these in extremely select cases. Limited evidence of use (see separate post about caregiver placebo effect)

Choosing the Right Therapy

No single therapy fits every case. Patient age, severity of OA, concurrent disease, caregiver expectations, and financial considerations all play a role in decision-making. For many patients, a multimodal strategy, combining lifestyle changes, rehabilitation, oral medications, and injectables, offers the best outcomes.