In December 2022, the U.S. Food and Drug Administration (FDA) approved Zycosan (pentosan polysulfate sodium injection) for the control of clinical signs associated with osteoarthritis in horses. The FDA wants to remind you of the benefits of FDA approval.

Drug Information

Zycosan is the first injectable pentosan product to receive FDA approval for use in horses. Zycosan is FDA-approved for intramuscular use in horses.

Zycosan is a heparin-like compound with anticoagulant and fibrinolytic effects. The mechanism of action for pentosan polysulfate sodium is unknown but is thought to include stimulation of hyaluronic acid and glycosaminoglycan synthesis in damaged joints, inhibition of proteolytic enzymes, and scavenging of free radicals. Pentosan polysulfate sodium may also modulate cytokine activity. 

Because pentosan polysulfate sodium is a weak anticoagulant, people who take an anticoagulant should use caution to prevent accidental self-injection when handling or administering Zycosan. 

Zycosan is a prescription animal drug containing 250 mg pentosan polysulfate sodium/mL. Zycosan is approved at a dosage of 3.0 mg/kg of body weight (1.4 mg/lb) administered once per week for four weeks. Zycosan is provided in single-use vials. Vials do not contain a preservative and should be discarded after use. Please refer to the Freedom of Information Summary and package insert for Zycosan for more information.

The FDA emphasizes the benefits of using FDA-approved drugs in your practice. FDA-approved drugs 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. When pentosan polysulfate sodium is indicated for use in an equine patient to control clinical signs of osteoarthritis, the FDA strongly encourages veterinarians to use the FDA-approved Zycosan. As with all approved animal drugs, the FDA will monitor and evaluate submitted adverse event reports for Zycosan, which would include monitoring for potential human safety risks associated with administration of pentosan polysulfate sodium. 

Benefits of FDA Approval

The FDA rigorously evaluates an animal drug before approving it. As part of the approval process, the drug company must prove to the FDA that:

  • There are data to support the drug is safe and effective for a specific use in the intended species;
  • The manufacturing process is adequate to preserve the drug’s identity, strength, quality, and purity; and
  • The drug’s labeling is truthful and not misleading.

The FDA’s role does not stop after the agency approves an animal drug. As long as the drug company markets the animal drug, the agency continues to monitor:

  • The drug’s safety and effectiveness (sometimes, the agency’s post-approval monitoring uncovers safety and effectiveness issues that were unknown at the time of approval);
  • The manufacturing process to ensure that the identity, strength, quality, and purity of the drug are maintained;
  • The drug’s labeling to make sure the information remains truthful and not misleading; and
  • The company’s marketing communications related to the drug to make sure the information is truthful and not misleading.

Safety and Effectiveness of Zycosan Compared to Compounded Forms of Injectable Pentosan Polysulfate Sodium

Animal drugs compounded from bulk drug substances are not FDA-approved drugs, nor are they FDA-approved generic drugs. The agency is aware that pentosan polysulfate sodium formulations compounded from bulk drug substances may be available through some compounding pharmacies. Unlike FDA-approved Zycosan, compounded and other unapproved formulations of pentosan polysulfate sodium have not been evaluated by the FDA for safety or effectiveness and may vary in quality, potency, and bioavailability. Additionally, due to the route of administration of injectable pentosan polysulfate sodium, it is important that it be a sterile formulation to ensure patient safety. The FDA cannot verify the sterility of the compounded products. 

In contrast to FDA-approved Zycosan, the absorption and bioavailability of compounded formulations of injectable pentosan polysulfate sodium are unknown and may be inadequate or variable. Further, while there are many post-approval requirements for sponsors of FDA-approved animal drugs, including the mandatory reporting of adverse drug experience reports, there are no such mandatory reporting requirements for compounded preparations. The FDA encourages veterinarians and animal owners to report adverse drug experiences and product defects associated with animal drugs and animal devices. More information about how to report information about animal drugs and devices can be found at our website: Report a Problem.

The FDA’s Center for Veterinary Medicine (CVM) is committed to promoting and protecting animal health by ensuring safe and effective drugs are available for animals. For more information, please contact


FDA’s Center for Veterinary Medicine

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