Comparison of Alfaxalone, Tiletamine/Zolazepam, and Dexmedetomidine Injectable Preanesthetics and Immersion in Tricaine Methanesulfonate (MS-222) for Surgical-Level Anesthesia in the Houston Toad (Anaxyrus houstonensis)
Maryanne E. Tocidlowski, DVM, DACZM
Thirteen clinically healthy Houston toads (Anaxyrus houstonensis), scheduled for euthanasia due to exposure to Chlamydia or Mycobacterium, were divided into three groups and used in a 3-week crossover anesthesia study comparing three injectable pre-anesthetic protocols (alfaxalone 15 mg/kg IM, tiletamine/zolazepam 5 mg/kg IM, and dexmedetomidine 0.1 mg/kg IM) followed by immersion into tricaine methanesulfonate (MS-222) to achieve anesthesia. Heart rates and respiration rates were recorded before injection and every 5 minutes post injection. Ten minutes after injection, toads were tested for righting reflexes and graded 1–3 (1—no righting response, 3—full righting response). Toads were then partially immersed into a buffered MS-222 solution at 800 ppm for 10 minutes. Ten minutes after immersion in buffered MS-222, toads were tested for righting reflexes and if none were noted, a toe pinch was used to evaluate deep pain sensation. Toads were graded 1–3 (1—no righting response or deep pain sensation, 3—full righting response). No complications were observed, and all toads recovered within 24 hours. Tiletamine/zolazepam showed the least change in heart rate over the 20-minute trial, whereas dexmedetomidine showed a profound decrease in heart rate. Respiration rates were similar for all three groups. Dexmedetomidine produced minimal sedation. Both alfaxalone and tiletamine/zolazepam resulted in sedation, but not at a surgical level, even after a 10-minute immersion into MS-222.