(Revised 12/5/03) Horse owners have a new option for treating equine protozoal myeloencephalitis (EPM) following the Nov. 19 U.S. Food and Drug Administration’s (FDA) approval of nitazoxanide. This medication has been under development as an EPM treatment for more than six years.

IDEXX Laboratories of Westbrook, Maine, received approval for the product, called Navigator, which is a 32% nitazoxanide antiprotozoal oral paste designed to kill the single-celled protozoan parasite Sarcocystis neurona, which infests the horse and causes EPM. (Read more on EPM at www.TheHorse.com/epm.)

Navigator is the second FDA-approved treatment to hit the equine market–Bayer’s Marquis (active ingredient ponazuril), another antiprotozoal oral paste, was the first FDA-approved EPM drug to be launched (August 2001). An additional type of treatment, diclazuril, awaits FDA approval.

Also in November 2003, Dorsey Kordick, PhD, of IDEXX laboratories based in Greensboro, N.C., gave a scientific presentation on Navigator’s safety and efficacy studies at the University of Kentucky Gluck Equine Research Center in Lexington, Ky. She explained that the treatment regimen lasts 28 days, and it begins with five days of half-strength doses, providing “a more gradual kill” of the parasite to allow intestinal microflora to adjust to the drug, and minimize the transient neurological worsening sometimes seen with extreme immune system stimulation (by numerous dead parasites). The horse should receive the dose once daily, just before he receives his grain concentrate.

Navigator’s mechanism of action shuts down cellular respiration of S. Neurona and works with the horse’s immune system to eliminate the parasite. Its cost to veterinarians should be comparable to other EPM treatments available