Zycosan® (Pentosan Polysulfate) for Horses

Published May 23, 2024
equine vet takes an ultrasound of a horse's joint while horse stands in front of him.

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PetMD’s medications content was written and reviewed by veterinary professionals to answer your most common questions about how medications function, their side effects, and what species they are prescribed for. This content shouldn’t take the place of advice by your vet.

What Is Zycosan® for Horses?

Zycosan® (active ingredient pentosan polysulfate) is an injectable veterinary medication prescribed for horses for the control of clinical signs due to osteoarthritis.

Zycosan® is the first pentosan injection that is FDA-approved for use in horses for relief of arthritis, which can cause lameness, stiffness, and joint swelling.

Zycosan® should not be used in horses who are hypersensitive to the active ingredient pentosan polysulfate or to any of the inactive ingredients.

Since Zycosan® has been shown to cause the blood to take longer than usual to clot (prolonged clotting times), it should not be used in horses with blood clotting disorders, in horses who are currently taking anti-clotting medications (anticoagulants or blood thinners), and in horses 24 hours before or after a surgical procedure.

Zycosan® should be used with caution in horses taking certain non-steroidal anti-inflammatory drugs (NSAIDs) that cause similar anti-clotting effects on the blood, as well as used cautiously in horses before or after strenuous activity.

It is important to note that at the time of this publication, the safe use of Zycosan® had not yet been evaluated in breeding, pregnant, or lactating horses, or horses younger than two years of age.

How Zycosan® Works in Horses

The way that pentosan polysulfate (active ingredient in Zycosan®) works is not fully understood but thought to help damaged joints increase the production of hyaluronic acid, a natural substance which helps lubricate and cushion the joint.

It may also decrease the levels of destructive substances (proteolytic enzymes and free radicals) and may block chemical messengers (cytokines) that promote harmful inflammation in the joint. Through these pathways, pentosan polysulfate has anti-inflammatory effects on diseased arthritic joints.

Zycosan® Directions for Horses

Follow the directions on the drug label or as provided by your veterinarian.

This medication is usually given as an injection into the muscle once weekly for four weeks for a total of four doses.

Long-term repeated use of Zycosan® had not yet been studied at the time of this publication.

Missed a Dose?

Speak with your veterinarian about what to do if you forget to give a dose of Zycosan®. Generally, they may instruct you to give it when you remember, or if it is almost time for your horse’s next dose, to skip the missed dose and resume your normal dosing schedule. Do not give extra or double doses.

Zycosan® Side Effects for Horses

Side effects of Zycosan® may include:

  • Pain, heat, swelling, redness at the area of the injection (injection site reaction)

  • Neck muscle cramping and reluctance to move the neck or head

  • Your horse’s blood taking longer than usual to clot (prolonged clotting times)

  • Decreased energy (lethargy)

  • Behavior changes: including aggression, stomping, pawing, agitation, anxiousness, overactivity, quietness, depression, or unsettledness

Horses treated with Zycosan® that are taking NSAIDs at the same time should be monitored for symptoms of abnormal bleeding, including nosebleeds, small purple or red dots in the skin (petechiae), and bruising due to broken blood vessels (ecchymosis).

Human Side Effects

Zycosan® is a prescription veterinary injectable medication not used in human medicine.

Due to possible side effects, humans should never use medicine dispensed for their animals and animals should not be given any medicine dispensed for a human’s use.

If you are currently taking a blood thinner (anticoagulant) medication, use caution when administering Zycosan® to prevent accidently self-injecting, due to its blood thinning effects. If you accidentally ingest or inject yourself with this medication, seek immediate medical attention and call your physician or the national Poison Control Center hotline at 800-222-1222.

If Zycosan® comes into contact with your skin, rinse your skin thoroughly with water and seek medical attention if needed.

Call Your Vet If:

  • Severe side effects are seen (see above)

  • Your horse's condition worsens or does not improve with treatment

  • You see or suspect an overdose

  • You have additional questions or concerns about the use of Zycosan®

Zycosan® Overdose Information for Horses

An overdose of Zycosan® may cause pain and swelling at your horse’s injection site, muscle spasms and stiffness, holding the head low, low energy, depression, decreased food intake, and longer than usual time to form normal blood clots (prolonged clotting times).

If you suspect an overdose, immediately contact your veterinarian, seek emergency veterinary care, or call an animal poison control center. Consultation fees often apply.

Pet Poison Helpline (855) 764-7661

ASPCA Animal Poison Control (888) 426-4435

Zycosan® Storage for Horses

Always confirm storage requirements by reading the prescription label.

Zycosan® should be stored at room temperature between 68‑77 F.

Zycosan does not contain a preservative, so leftover unused contents in the vial should be discarded.

Keep out of reach of children and pets.


What does Zycosan® do for horses?

Zycosan® helps relieve the clinical signs of osteoarthritis, such as lameness, stiffness, and joint swelling.

How often should I give my horse Zycosan®?

Follow the directions on the drug label or as provided by your veterinarian. This medication is usually given as an injection into the muscle once weekly for four weeks for a total of four doses.

No vet writer or qualified reviewer has received any compensation from the manufacturer of the medication as part of creating this article. All content contained in this article is sourced from public sources or the manufacturer.


Plumb DC. Pentosan Polysulfate (PPS). Plumb’s Veterinary Drugs. Updated April 2023. Accessed April 28, 2024.


Molly Price, DVM


Molly Price, DVM


Dr. Molly Price has practiced small animal medicine for over 20 years and is a graduate of Texas A&M College of Veterinary Medicine. She...

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