For horses already suffering from EPM, a drug once thought to hold out great hope to people with AIDS for treatment of a protozoan?caused diarrhea may prove effective in the treatment of EPM.

The drug, nitazoxanide, has been studied by scientists in association with Blue Ridge Pharmaceuticals (BRP) in Greensboro, North Carolina. BRP is awaiting US Food & Drug Administration approval for use of the drug in horses.

"We're in the review process," said Scott Moffitt, BRP's director of equine marketing. The federal review process for a new drug can be lengthy and is unpredictable in any case, but in this case the process has been more complex, he said.

"Particularly with an emerging disease like this, there are more questions than there are answers, and it makes it more difficult for everybody," said Moffitt.

Nitazoxanide is used in Mexico and Mali to treat cryptosporidial diarrhea in individuals with advanced HIV disease. Cryptosporidium parvum is a protozoan parasite that is very difficult to eliminate once it becomes "interiorized" in the cell walls of the intestine.

According to documents on file with the US FDA, nitazoxanide has broad?spectrum activity against a host of bacteria and parasites such as nematodes, cestodes, and trematodes. The application by Unimed Pharmaceuticals to have nitazoxanide (NTZ) approved for use in AIDS patients was rejected in 1998 after the company failed to produce sufficient data of placebo?controlled studies on the drug's efficacy.

Clara K. Fenger, DVM, PhD, of Equine Internal Medicine Consulting in Georgetown, Kentucky, reported on one study at the American Association of Veterinary Parasitologists Association meeting last year. Dr. Fenger could not be reached for comment.

In Fenger's study, the researchers conducted two field trials of the drug. Horses enrolled in the clinical trial had to show significant asymmetric ataxia (lack of coordination on one side, for example, grade 2?4) three positive Western Blot tests for cerebrospinal fluid (see story, page 2) for EPM from at least two laboratories, complete blood count and chemistry profile, and a normal physical examination other than neurological signs.

All horses in the trial received 24 mg/kg NTZ orally once a day for five days, followed by 50 mg/kg NTZ orally once a day for another 23 days.

Of 63 horses that completed the trial, 70 percent (or 44) showed improvement in neurological signs. Thirteen percent (eight horses) had a negative CSF Western blot test at completion. By the 85 day cut?off, three horses had relapsed.

In the broader field trial, 23 horses completed the trial, with 21 showing improvement by the end of the trial.

Side effects of the drug reported for this last trial included fever (15 horses), increased digital pulse (four horses), temporary worsening of neurologic signs (four horses), and colic (one horse).

"No side effects were severe, or persisted beyond several days," according to the researchers.

More information on EPM is available in International Equine Science's 16-page report on the disease. The report covers the latest research on causes, prevention, and treatment of EPM and costs $14.95 plus $2.00 S&H.

This article originally appeared in the February 2001 issue of International Equine Science. IES, an eight-page newsletter, provides the latest scientific information on the athletic horse - an advertising-free and quick-to-read monthly update on equine research. www.equinescience.com (802)888-6189.

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