Abstract

Enrofloxacin is a fluoroquinolone antibiotic with activity against many of the gram-negative bacteria that cause illness in amphibians; however, there are few studies evaluating its oral or transcutaneous absorption in this group of animals. This study evaluates the liver tissue concentrations of enrofloxacin, and its active metabolite ciprofloxacin, after oral and topical dosing in endangered Houston toads (Anaxyrus [Bufo] houstonensis). Liver concentrations were used as a surrogate marker for plasma concentrations to assess absorption. Administration of enrofloxacin by dusting crickets with powdered enrofloxacin 68 mg liver-flavored tablets^a at target dosages of 10 mg/kg resulted in combined enrofloxacin/ciprofloxacin tissue concentrations above 1.0 µg/gm, up to 24 hours post treatment. Administration of a 5 mg/L enrofloxacin liquid^b to the backs of toads by use of a spray bottle also produced enrofloxacin/ciprofloxacin tissue concentrations above this value for up to 10 hours post treatment. In addition, these methods of administration once daily for up to 12 weeks produced no signs of adverse effects in these toads. Increased concentration of the topical spray to 10 mg/L enrofloxacin did not proportionately increase tissue concentrations. These methods of administration can be of benefit to veterinarians for amphibian conservation programs which house large numbers of small amphibians where individual treatment of animals is time-prohibitive, provided additional pharmacokinetics of topical and oral enrofloxacin in amphibians can be performed to refine the dose.

Endnotes

a. Baytril 68 mg liver-flavored tablets; Bayer Health Care, LLC, Shawnee Mission, KS, USA
b. Baytril 100 mg/ml injectable solution; Bayer Health Care, LLC

Acknowledgments

This study was funded by a grant from the Houston Zoo Staff Conservation Fund. The authors would like to thank Dr. Joseph Flanagan for assistance with sample collection; Aleyda Galan and Chris Bednarksi for assistance with enrofloxacin dosing and toad husbandry; and Houston Zoo Veterinary Staff Stephanie Fannin, Kara LaVictoire, and Ryanne Henigar for assistance processing and packaging samples.