When a horse has to be on an antibiotics for long periods, the oral route of administration is preferable. However, the choices available to horse owners are limited. Cornelia D. Nieuwoudt, PharmD, director of the pharmacy at Texas A&M University and formerly with Johns Hopkins University, discussed using a gel formulation of the antibiotic enrofloxacin in horses at the 50th annual American Association of Equine Practitioners (AAEP) Convention in Denver, Colo., Dec. 4-8, 2004.

Nieuwoudt said enrofloxacin offers a broad spectrum of activity. For her study, she used a cattle enrofloxacin injectable that she reformulated into an oral, flavored gel. She believes this would not be difficult for veterinarians in the field to do.

She found that the formulated enrofloxacin gel maintained its full potency for three months (the length of her trial) if it was protected from light and stored at room temperature, or if it was stored in a refrigerator. Refrigeration is preferred over room temperature, if possible. When exposed to heat, the formulation was not very stable and lost potency very quickly. Nieuwoudt also found that the active ingredient was absorbed by the horse via the oral route and produced serum concentrations sufficient to treat infections caused by a variety of bacteria. However, it is always prudent to use an antibiotic with the narrowest spectrum of activity, if at all possible.

While there were few complications, some horses developed mouth lesions, which could be avoided by rinsing the horse's mouth with water after gel administration. Although not observed in this trial, the use of any antimicrobial can, in some instances, result in diarrhea. She said it is advisable to schedule dosing after fasting the horse for 12 hours, which is not difficult if the horse is stalled overnight