Enrofloxacin was administered as a single dose (dosage of 15 mg/kg) to eight red-tailed hawks (Buteo jamaicensis) and five great horned owls (Bubo virginianus) by the oral (in prey) or intramuscular route, and was administered to eight red-tailed hawks by the intravenous route. The disposition of enrofloxacin was evaluated in serial plasma samples up to 48 hours after administration (before dosing, 0.25, 0.5, 1, 2, 4, 8, 12, 24, and 48 hours after dosing).
Oral administration was accomplished by force-feeding the raptor with a small mouse that had been injected intraperitoneally with an injectable formulation of enrofloxacin (Baytril®, 22.7 mg/ml, Bayer Corp., Shawnee Mission, KS, USA). Oral administration resulted in plasma concentrations of enrofloxacin that peaked at 4–12 hours after dosing. Enrofloxacin levels remained above typical gram-negative bacterial pathogens’ MIC90 for at least 18 hours after oral administration, although there was an initial lag time of approximately 4 hours for absorption from the gastrointestinal tract.
Intramuscular enrofloxacin was administered into the pectoral musculature, with the dose divided between two sites. Intramuscular administration resulted in plasma concentrations that peaked at 0.5–2 hours after dosing; enrofloxacin levels remained above MIC90 for at least 12 hours after intramuscular administration.
Enrofloxacin was administered intravenously to eight red-tailed hawks via jugular vein, basilic vein or medial metatarsal vein. In these hawks, enrofloxacin levels remained above MIC90 for at least 15 hours after intravenous administration.
Two great horned owls were administered enrofloxacin intravenously via basilic vein; these owls showed acute weakness, tachycardia, and peripheral vasoconstriction during injection, as an apparent direct effect of enrofloxacin. The owls’ clinical signs resolved by 1–3 hours after injection, after they were treated with intravenous and subcutaneous fluids, atropine, and oxygen.
It appears that oral (in-prey) and intramuscular routes are reliable and effective means of administration of injectable enrofloxacin in red-tailed hawks and great horned owls, using a dosage of 15 mg/kg every 24 hours for most susceptible bacterial pathogens. Intravenous administration can be performed with caution in red-tailed hawks, but should not be attempted in great horned owls. The exact reason for great horned owls’ adverse reaction to intravenous enrofloxacin is unknown.
The authors would like to thank the following volunteers for their help in performing this study: Kathleen Creighton, Sean Goodell, Heather Graves, Kristine Jensen, Kevin Kwak, John O’Keeffe, Michael Schindel, Rebecca Stanton, Sam Tanng, Mary Beth Wood, and Jennifer Yamamoto.