New Treatment for Endotoxemia

Michelle Henry Barton, DVM, PhD, of the University of Georgia, recently completed a project on treating endotoxemia with polymyxin B (PMB), an alternative to endotoxin antibody products. The drug PMB kills many Gram-negative bacteria and also binds endotoxin, preventing interaction of endotoxin with white blood cells (WBC) as do endotoxin antibody products--thus heading off the damaging effects created by that reaction.

"The expense, adverse reactions, and occasional failures (of endotoxin antisera) have directed our attention toward the use of PMB instead," she says.

Gram-negative bacteria in the horse's hindgut help break down fibrous feeds. Endotoxemia occurs when toxins from Gram-negative bacteria get out of the intestine and into the bloodstream. (Endotoxin originates from the outer cell membrane of bacteria.) The intestinal lining usually provides a safe barrier to the rest of the body, but if the integrity of the gut wall is compromised, endotoxins can enter the bloodstream. When the immune system overreacts to the toxins, the result is endotoxemia. Endotoxin becomes concentrated on the surface of WBC, causing them to secrete inflammatory agents. Massive release of these agents cause the horse to go into shock.

Once the process begins, it can be difficult to reverse it and save the horse. Halting further production of inflammatory agents could make the difference in whether the horse can recover. "Even when used hours after the onset of endotoxemia, PMB reduces synthesis of damaging chemicals and improves survival rates," says Barton. "The affordability and ease of administration of PMB provide considerable promise for its clinical use."

The drug PMB is an effective treatment for endotoxemia in horses, says Barton, but has side effects--it can damage the kidneys and nervous system. She found that when the drug is given at lower doses than prescribed to kill bacteria, "it maintains its endotoxin-binding properties without producing the adverse side effects." She cautioned that PMB should be used with care in endotoxemic patients with pre-existing kidney or neurologic damage, as repeated use might exacerbate underlying disease.

The drug is most beneficial when given early. "It is an affordable alternative to endotox 0in serum for prophylactic (preventive) treatment in patients with colic caused by grain overload or Gram-negative sepsis if given at the beginning of antimicrobial therapy, and prior to surgery in patients with strangulated bowel," says Barton. "At the onset of endotoxemia, PMB still has beneficial effects (binding and neutralizing endotoxin), but benefit from the drug is likely to diminish one to two days after endotoxemia begins." Other treatments should also be used to help control effects of endotoxemia, researchers noted.

Investigations into alternative formulations with fewer side effects are ongoing with promising results, said Barton.

About the Author

Heather Smith Thomas

Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog,, she writes a biweekly blog at that comes out on Tuesdays.

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