Preliminary Single-Dose Pharmacokinetics of Enrofloxacin after Oral and Intramuscular Administration in Green Iguanas (Iguana iguana)
Enrofloxacin (Baytril; Bayer Corp., Shawnee, KS) is a broad-spectrum fluoroquinolone antibiotic with good activity against many gram-negative bacteria and some gram-positive bacteria. Its use in green iguanas has previously been empirical as no enrofloxacin pharmacokinetic studies have been published in any lizard. In this study, six green iguanas, ranging in size from 374–1740 g, were given injectable enrofloxacin PO at 5 mg/kg. Three iguanas (672–916 g) were given enrofloxacin at 5 mg/kg IM. Blood samples were taken at 0, 0.5, 1, 3, 6, 12, 24, 48, 72, and 96 hours post-administration. The plasma concentrations of both ciprofloxacin and enrofloxacin were measured using high-performance liquid chromatography (HPLC). After oral and IM administration, the plasma concentration-time curve followed a two-compartment model. The elimination half-life of enrofloxacin was 22.3±11.3 hours (x ± SD) after PO administration and 26.0±10.2 hours after IM administration. Enrofloxacin was absorbed fairly rapidly with a mean time to reach peak plasma concentration of 2.7±2.6 hours following oral administration and 1.0±0 hours following IM administration. The mean maximal plasma concentration (Cmax) achieved was 1.16±0.54 µg/ml after oral administration and 2.03±0.52 µg/ml after IM administration. While therapeutic enrofloxacin plasma concentrations (>0.2 µg/ml) were obtained in all iguanas administered enrofloxacin, there was considerable variability in the time that enrofloxacin was maintained at or above therapeutic levels following oral dosage. Therapeutic enrofloxacin plasma concentrations were maintained for 31.7±32.1 hours after oral administration and 16±6.9 hours following IM administration. As plasma ciprofloxacin levels were always below the limit of quantitation of the assay and usually below the limit of detection, enrofloxacin does not appear to be metabolized to ciprofloxacin in significant amounts in green iguanas. Although therapeutic plasma enrofloxacin concentrations were achieved following oral administration, the marked variability of the pharmacokinetic parameters of enrofloxacin after oral administration may make the parenteral route more suitable for the treatment of critical infections in green iguanas.