You’ve probably read warnings about the risks of administering compounded drugs (in which the preparation, strength, or flavor has been changed to meet a patient’s particular therapeutic requirement) to horses: lack of federal regulations, inconsistent quality, and so forth. But these medications do serve an important purpose.

For mares with endometritis, for instance, a compounded form of the antibiotic enrofloxacin might cause fewer side effects than the commercial product. Researchers from Washington State University (WSU) teamed up with veterinarians at Rood & Riddle Equine Hospital, in Lexington, Kentucky, to find out.

"Endometritis—an inflammation of the endometrium that lines the mare’s uterus—is a common cause of low pregnancy and foaling rates," explained presenting author Lisa Pearson, DVM, MS, Dipl. ACT, a theriogenologist at WSU’s College of Veterinary Medicine, during the 2014 American Association of Equine Practitioners Convention, held Dec. 6-10 in Salt Lake City, Utah.

Enrofloxacin is an effective treatment against almost all of the bacteria isolated from endometritis cases. Pearson and her colleagues observed in a previous study, however, that mares developed severe hemorrhagic inflammation and fibrosis (scarring) in their endometrium in response to intrauterine commercial enrofloxacin (Baytril-100) administration. She said the product’s high pH level can be caustic to the endometrium