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What is Pentosan Allergy?

Pentosan is produced from the hemicellulose of beechwood. It can be formulated as a calcium derivative or a sodium salt. It is currently not approved by the FDA in the United States as an injection for horses. Pentosan has been used for more than 30 years in Australia and parts of Europe.  

The calcium derivative form of pentosan is absorbed orally and subcutaneously. The sodium salt derivative is primarily given intramuscularly. There can be slight swelling at the injection site that will usually diminish within a few days. Horses that are allergic to pentosan should not be given any medication that contains pentosan. Allergic reactions are more likely to occur in horses who are recovering from surgery, have autoimmune problems or have prior bleeding issues.

Pentosan, or pentosan polysulfate, was initially used as an antithrombotic agent that helped to prevent blood clots in humans. It was also found to have anti-lipidemic properties that helped to prevent fat buildup in blood vessels. In horses, pentosan is used to improve the symptoms of osteoarthritis. There is strong evidence that pentosan can significantly improve the lameness in racehorses.

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Symptoms of Pentosan Allergy in Horses

Since pentosan was initially used as an antithrombotic and anti-lipidemic agent, horses that are known to have clotting defects or have had traumatic hemorrhaging should not be given it. These symptoms can be life-threatening and will require veterinary attention. If you notice your horse exhibiting any of these symptoms, contact your veterinarian immediately for an assessment. 

  • Swelling in the neck
  • Difficulty breathing
  • Blood unable to clot

Causes of Pentosan Allergy in Horses

Pentosan has the active ingredient of pentosan polysulfate or PPS. It was initially developed as an antithrombotic agent that kept blood from clotting. In horses, regular administration of pentosan will reduce the clinical symptoms of osteoarthritis. It is not currently FDA approved in the United States and is available as a generic product through compounding labs. 

Pentosan is usually administered by intramuscular injection. It can be administered orally or subcutaneously as well. It is formulated as either a calcium derivative or a sodium salt derivative. Most pentosan that is available in the United States is to be given by injection, not orally.

Horses that have known clotting defects should not be given pentosan. Horses that have an infection or are in renal or hepatic failure should also not be given this medication. Pentosan should not be given to horses that have had surgery within the past 48 hours.

Diagnosis of Pentosan Allergy in Horses

When your veterinarian arrives, they will begin by asking about any medications that your horse is currently taking as well as any supplements that you give. A complete medical history will also be taken so your veterinarian can begin pinpointing the cause of your horse’s symptoms. 

A full physical examination will be completed, with your veterinarian paying close attention to any swelling in the neck. If your horse was given pentosan through an injection, your veterinarian may notice swelling at the injection site. A complete blood count and a biochemistry panel will be conducted to determine your horse’s clotting abilities. 

Symptoms may not appear immediately following the administration of pentosan and this can make it more difficult for your veterinarian to determine if your horse is suffering from a pentosan allergy.

Treatment of Pentosan Allergy in Horses

Your veterinarian will begin supportive care immediately following diagnosing pentosan allergy in your horse. In severe cases, hospitalization will be strongly recommended for continual monitoring. 

If your horse is experiencing clotting difficulties, your veterinarian will administer medications to reverse the effects and allow your horse’s blood to begin naturally clotting. Your veterinarian will keep your horse hospitalized until they feel that your horse is recovering well from their allergic reaction to pentosan.

Recovery of Pentosan Allergy in Horses

At home care will be necessary for milder cases of pentosan allergy where your horse did not need to be hospitalized. Your veterinarian will discuss care instructions with you.

Immediate treatment is necessary if your horse is having difficulty with their blood not clotting properly or difficulty breathing. These would probably be considered severe cases that need hospitalization to stabilize your horse.

Discontinue use of pentosan immediately and make sure that your veterinarian has the allergy on file. When you give your horse their first treatment of pentosan, have your veterinarian there or on standby in case your horse does experience immediate problems. Closely monitor your horse after they receive their pentosan for several days so you can catch any allergic reaction quickly.