Compounded Enrofloxacin: Safe and Effective for Use in Mares

Compounded Enrofloxacin: Safe and Effective for Use in Mares

Enrofloxacin is an effective treatment against almost all of the bacteria isolated from endometritis cases.

Photo: Sara Lyle, DVM, PhD, Dipl. ACT

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.

"We decided to collaborate with Rood & Riddle to determine the effects of a three-day intrauterine infusion of an alcohol-free, water-based enrofloxacin suspension on the endometrium," Pearson said, which they theorized would not have the same caustic effects as the commercial product.

In their study, they administered this compounded version (at 2.5 mg/kg) to eight healthy embryo transfer recipient mares in estrus. They used transrectal ultrasound, vaginal exam, endometrial biopsies, and cytology and bacteriology during and after treatment to evaluate the drug's effects on the mares' reproductive tracts.

Pearson said the water-based enrofloxacin was associated with "a transient (short-lived), but not statistically significant, inflammatory response," as well as a significant increase in intrauterine fluid and its echogenicity (reflection of the ultrasound signal). Anytime you put something into the uterus, it causes a response—the fact that this one resolved quickly is a positive sign, Pearson explained.

"Compared to the commercial product, we did not see severe, long-standing, permanent changes to the uterus," she said.

Twenty-one days post-treatment, all mares had negative bacterial cultures, indicating the drug is also effective.

"These findings suggest that a water-based enrofloxacin suspension may be useful for treatment of bacterial endometritis sensitive to enrofloxacin without the deleterious effects seen with administration of the commercial product," she explained.

Further, "this drug is useful for bacteria which are resistant to other commonly used antibiotics and can potentially be used to treat drug-resistant infections in mares," Pearson said.

About the Author

Alexandra Beckstett, The Horse Managing Editor

Alexandra Beckstett, Managing Editor of The Horse and a native of Houston, Texas, is a lifelong horse owner who has shown successfully on the national hunter/jumper circuit and dabbled in hunter breeding. After graduating from Duke University, she joined Blood-Horse Publications as Assistant Editor of its book division, Eclipse Press, before joining The Horse.

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