Pharmacokinetics and pharmacodynamics of intramuscular alfaxalone in central bearded dragons (Pogona vitticeps): effect of injection site.

OBJECTIVE

To evaluate the pharmacodynamic effects and pharmacokinetics of a single intramuscular (IM) injection of alfaxalone in central bearded dragons (Pogona vitticeps) when injected at a cranial versus a caudal site.

STUDY DESIGN

Prospective, masked, randomized crossover study.

ANIMALS

A total of 13 healthy bearded dragons weighing 0.48 ± 0.1 kg.

METHODS

Alfaxalone (10 mg kg) was administered IM to 13 bearded dragons in the triceps muscle (cranial treatment) or the quadriceps muscle (caudal treatment) separated by 4 weeks. Pharmacodynamic variables included movement score, muscle tone score and righting reflex. Blood was obtained from the caudal tail vein using a sparse sampling methodology. Plasma alfaxalone concentrations were determined using liquid chromatography-mass spectrometry, and pharmacokinetic analysis was performed using nonlinear mixed-effects modeling. Differences in variables between injection sites were analyzed using a nonparametric Wilcoxon signed-rank test for paired data with significance set at p ≤ 0.05.

RESULTS

Time to loss of righting reflex score was not different, median (interquartile range), between cranial and caudal treatments [8 (5-11) and 8 (4-12) minutes, respectively, p = 0.72]. Time to recovery of righting reflex was also not different between cranial and caudal treatments [80 (44-112) and 64 (56-104) minutes, respectively, p = 0.75]. Plasma alfaxalone concentrations were not significantly different between treatments. The population estimate (95% confidence intervals) for volume of distribution per fraction absorbed was 1.0 (0.79-1.20) L kg, clearance per fraction absorbed was 9.6 (7.6-11.6) mL minute kg, absorption rate constant was 2.3 (1.9-2.8) minute and elimination half-life was 71.9 (52.7-91.1) minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

Regardless of the injection site, IM alfaxalone (10 mg kg) produced reliable chemical restraint in central bearded dragons, appropriate for nonpainful diagnostic procedures or anesthetic premedication.