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U.S. Department of Health and Human Services

Animal & Veterinary

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FDA Veterinarian Newsletter September/October 2001 Volume XVI, No V

FDA has approved Marquis (ponazuril) the first drug to treat equine protozoal myeloencephalitis (EPM) in horses. EPM is caused by a parasite (Sarcocystis neurona) and is the most commonly diagnosed neurological condition in horses in America. EPM is widespread in North America, South America, and in Canada. In some areas of the United States, as much as 80-90% of the horse population may have been exposed to EPM. An estimated one percent of the horses exposed to the disease will develop clinical signs of EPM and require treatment.

The clinical signs of EPM may vary, and they may include weakness (particularly on one side), serious lack of coordination, and muscle wasting involving all four limbs. EPM is more prevalent in young (less than 5 years of age) and older horses (more than 13 years old). Diagnosis of EPM is difficult since there are at least four other central nervous system diseases which can closely resemble the disease.

FDA expedited the approval process for ponazuril because it was intended to reduce the suffering and death associated with EPM, and be cause there were no approved therapeutics for treating this devastating disease.

Ponazuril is supplied as an oral paste to be given once at day at the dose of 5 mg/kg for 28 days in adult horses. Bayer Animal Health, Shawnee Mission, Kansas, is the sponsor of the drug that will be available by prescription only from a licensed veterinarian.