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

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ObjectiveTo 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 designProspective, masked, randomized crossover study. AnimalsA total of 13 healthy bearded dragons weighing 0.48 ± 0.1 kg. MethodsAlfaxalone (10 mg kg–1) 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. ResultsTime 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–1, clearance per fraction absorbed was 9.6 (7.6–11.6) mL minute–1 kg–1, absorption rate constant was 2.3 (1.9–2.8) minute–1 and elimination half-life was 71.9 (52.7–91.1) minutes. Conclusions and clinical relevanceRegardless of the injection site, IM alfaxalone (10 mg kg–1) produced reliable chemical restraint in central bearded dragons, appropriate for nonpainful diagnostic procedures or anesthetic premedication.