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  1. CVM Updates

FDA Approves First Injectable Pentosan for Osteoarthritis in Horses


December 20, 2022

Today the U.S. Food and Drug Administration approved Zycosan (pentosan polysulfate sodium injection) for the control of clinical signs associated with osteoarthritis in horses. Zycosan is a heparin-like compound and is the first injectable pentosan product to receive FDA approval. 

Osteoarthritis involves the slow breakdown of joint cartilage, which can result in a variety of clinical signs such as lameness, stiffness, and joint swelling. While there is no cure for osteoarthritis, appropriate management can help control the clinical signs of osteoarthritis in horses and improve their quality of life.

Zycosan will be an important addition to the available approved drugs to control the clinical signs of osteoarthritis in horses. Unapproved injectable formulations (including compounded formulations) of pentosan have a long history of use in horses, but Zycosan is the first injectable pentosan product to have met the FDA’s standards. FDA-approved drugs, like Zycosan, have been demonstrated to be safe and effective for their intended use and have been consistently manufactured to preserve the drugs’ identity, strength, quality, and purity. The FDA strongly encourages veterinarians to use the legally marketed FDA-approved Zycosan when pentosan is indicated for use in an equine patient. 

The sponsor of Zycosan conducted a field study in client-owned horses that had lameness in one leg and were diagnosed with osteoarthritis in the lame leg. Horses in the treatment group received Zycosan by intramuscular injection in the neck once every seven days for four weeks for a total of four doses. Horses in the control group were given an equal volume of saline at the same dosage regimen.

Each horse’s lameness was graded on Days 0 and 28 of the study. On Day 28, more horses in the Zycosan treated group had improved lameness grades compared to the control group and the study results indicated that treatment with Zycosan at the labeled dose benefited horses with single limb lameness due to osteoarthritis. 

The most common adverse reactions associated with the administration of Zycosan were injection site reactions (pain, heat, swelling, redness, and neck muscle cramping) and prolonged coagulation parameters (activated partial thromboplastin time (aPTT) and prothrombin time (PT)). Some injection site reactions initially occurred around the time of dosing (peri-dosing) and other injection site reactions were initially delayed (up to three days after dosing). All peri-dosing reactions resolved without specific treatment. All delayed reactions resolved within five days from onset and most didn’t require treatment. Clinical signs of bleeding were not seen in any horses.

Zycosan is only available with a veterinary prescription because professional expertise is required to diagnose osteoarthritis, properly administer the injection, and monitor the safe use of the product, including treatment of any adverse reactions.

Zycosan is for intramuscular use in horses only and is not for use in humans. Because pentosan polysulfate sodium is a weak anticoagulant, people who take an anticoagulant should use caution when handling or administering Zycosan.

Zycosan should be administered at a dose of 3 mg/kg (1.4 mg/lb) by intramuscular injection once weekly for four weeks (for a total of four doses). Zycosan is supplied in a 7.5 ml single use vial.

Zycosan is sponsored by Anzac Animal Health LLC, based in Maryland Heights, Missouri.

For more information:

Issued by FDA Center for Veterinary Medicine.
For questions, Contact CVM.

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