Intramuscular Alfaxalone Effective Dose (ED) Determination and Cardiopulmonary Effects of ED99 in Sonoran Desert Toads (Incilius alvarius)

There is limited knowledge on amphibian sedation, and drug doses appear to be species-specific and affected by the administration route. Alfaxalone, a neuroactive steroid, has gained popularity in veterinary medicine and has been evaluated in some amphibian species. Previous studies in amphibians have demonstrated a sedative dose range of 10-30 mg/kg IM. No peer-review publication has investigated this drug in Sonoran Desert toads specifically. Therefore, the purpose of this study was to 1) determine the effective dose 50 (ED50) of IM alfaxalone for sedation and 2) determine the cardiopulmonary effects of the effective dose 99 (ED99) in 13 Sonoran Desert toads. Using the Dixon’s Up-and-Down method, the ED50 was calculated as 9.02 mg/kg while using a non-linear regression, the calculated ED50 was 9.65 mg/kg, and the ED99 was 9.91 mg/kg. Based on these results, 10 mg/kg IM was administered, and its cardiovascular effects were determined for 120 mins post-injection. The 10 mg/kg IM dose resulted in significant transient cardiorespiratory depression in all toads, with most toads (11/13) showing signs of sedation (recumbency and/or loss of righting reflex) within 30–40-minutes post-injection. There was no associated mortality with this study, and the side effects associated with this dosage (cardiorespiratory depression, ventral erythema, dysphoric behavior such as rolling and head pressing) resolved in all toads prior to the end of the 120-minute observation window. This study hopes to increase the understanding of the clinical application and limitations of this drug for sedation of Sonoran Desert toads.