EPM: Is DMSO the Cure for Treatment Issues?

New research on treating horses with equine protozoal myeloencephalitis (EPM) has found dissolving toltrazuril sulfone, commercially known as ponazuril, in dimethylsulfoxide (DMSO) instead of water prior to oral administration in horses increases the bioavailability by three times and achieves therapeutic levels in both the blood and cerebrospinal fluid.

Ponazuril and related triazine-based antiprotozoal agents used to treat horses with EPM are highly lipid (fat) soluble. As a result, these agents dissolve poorly in the gastrointestinal system and are therefore poorly absorbed.

Poor drug absorption results in variable drug concentrations in the bloodstream, which translates into a variable therapeutic effect in the treated horse, explained Levent Dirikolu, DVM, PhD, from the Department of Veterinary Biosciences at the University of Illinois, and co-researchers from the University of Kentucky Gluck Equine Research Center and the United States Department of Agriculture (USDA) Animal and Natural resources Institute.

"In addition, it is difficult to predict and control drug concentrations at any given dose," added Dirikolu.

Since DMSO has been used to enhance drug absorption previously, Dirikolu and his colleagues dissolved toltrazuril sulfone (ponazuril) in DMSO to determine if oral bioavailability of the drug was improved.

"As hypothesized, DMSO increased the bioavailability of toltrazuril sulfone markedly," said Dirikolu.

These findings will enable equine veterinarians to:

  • Routinely achieve predictable therapeutic levels of the drug in both the blood and cerebral spinal fluid;
  • Administer loading doses of toltrazuril sulfone in acute cases of EPM, or;
  • Administer toltrazuril sulfone in DMSO mixed with feed.

Further studies on the clinical efficacy, toxicity, and determining the most appropriate therapeutic window for triazine-based agents for EPM are still needed.

The study, "Synthesis and detection of toltrazuril sulfone and its pharmacokinetics in horses following administration in dimethylsulfoxide" will be published in the Journal of Veterinary Pharmacology and Therapeutics in August 2009.

      About the Author

      Stacey Oke, DVM, MSc

      Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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