The pentosan polysulfate (PPS) injectable product Zycosan (manufactured by Anzac Animal Health LLC) was approved by the FDA in December 2022 to “control clinical signs associated with osteoarthritis in horses.” Pentosan polysulfate is a semisynthetic polysulfated xylan, which is a polysaccharide consisting mostly of xylose, a type of simple sugar.

During the 2022 American Association of Equine Practitioners Convention, held Nov. 18-22 in San Antonio, Texas, Scott McClure, DVM, PhD, Dipl. ACVS, ACVSMR, of Midwest Equine Surgery and Sports Medicine, in Boone, Iowa, presented details on the field trial that was conducted as part of the FDA approval process.

That field trial included client-owned horses with radiographic evidence of osteoarthritis in a single joint. Horses were randomly assigned to either a control (receiving saline) or treatment (PPS) group that was administered 3 mg/kg PPS intramuscularly (IM) once weekly for four consecutive weeks. They evaluated horses on Days 0, 7, 14, and 28, and the owners assessed them daily. Ten days after the last exam, the veterinarians performed a final follow-up phone call to the owners.

In total, 219 horse aged 3 to 32 years completed the study.

“Treatment success rate was 60% in PPS-treated horses compared with only 36% of saline-treated horses, meaning that horses improved at least one lameness grade over the course of the 28-day study,” relayed McClure.

He said they identified no concerns related to PPS’s anticoagulant (mild heparin-like) properties (i.e., not blood clotting abnormalities were appreciated). Specifically, prothrombin time, activated partial thromboplastin time (two indicators of how long it takes for blood to clot), and fibrinogen (a clotting factor) were within the reference ranges throughout the study.

Unrelated to blood clotting, blood urea nitrogen (BUN) and mean corpuscular hemoglobin (MCH, the average amount of the oxygen-carrying protein hemoglobin in each red blood cell, were both significantly higher in the treatment group. Those increases, however, were likely spurious and not clinically significant, said McClure. They were simply noted for full transparency regarding this product.

“What was interesting was the significant decrease in globulins, total protein, neutrophils, and white blood cell count in the PPS-treated horses,” he said. “There is no singular explanation for this finding, but it does suggest a whole-body decrease in inflammation. This may mean we are not treating just the single joint with OA, and this is certainly an area that needs to be looked at a little more.”

Finally, fewer than 10% of horses had injection site reactions, as you’d expect with any IM injection, he said.

Wrapping up his presentation, McClure said, “PPS at 3 mg/kg is both safe and effective for OA in horses when administered IM once a week for four weeks. The data also suggest that this product can be used prophylactically (preventively).”