Evaluation of MS-222 (Tricaine Methanesulfonate) and Propofol as Anesthetic Agents in Sonoran Desert Toads (Bufo alvarius)

Abstract

Toads in the genus Bufo are commonly kept in pet, research, and zoological settings and may require anesthesia during veterinary care. Limited information is available comparing anesthetic protocols in most amphibian species. The purpose of this study was to evaluate the clinical and cardiopulmonary effects of tricaine methanesulfonate (MS-222) and propofol in Sonoran desert toads (Bufo alvarius). Nine juvenile Sonoran desert toads were anesthetized with an immersion bath of 1 g/L MS-222 and 35 mg/kg intracoelomic propofol with a minimum 2-wk wash-out period between trials. Heart rate, respiratory rate, and reflexes (righting, escape, corneal, superficial pain, and deep pain) were monitored every 5 min for the first 90 min and then every 10 min for the next 90 min during both anesthetic trials. Surgical anesthesia was defined as complete loss of all measured reflexes. MS-222 produced surgical anesthesia in 100% (9/9) of toads, whereas propofol produced surgical anesthesia in 11.1% (1/9). Mean induction time for the MS-222 trial was 19.9 min (SD: 5.4, Min–Max: 13–30), with mean duration of surgical anesthesia 23.9 min (SD: 10.8, Min–Max: 10–42). Mean recovery time after removal from the MS-222 bath was 85.3 min (SD: 18.5, Min–Max: 60–110). Righting reflex was lost in all animals in the propofol trial at a mean of 23.9 min (SD: 5.5, Min–Max: 20–35) following administration. A single animal in the propofol trial reached a surgical plane of anesthesia at 25 min post-administration, with surgical anesthesia lasting for 50 min. Mean time to recovery following administration of propofol was 145 min (SD: 47.2, Min–Max: 60–180); one toad was not fully recovered at the end of the monitoring period. Heart rate was not found to significantly (P > 0.05) change from baseline at any monitoring point for either anesthetic protocol. Respiratory rate was found to decrease significantly (P < 0.05) at all time points between 5 and 65 min in the MS-222 trial and between 10 and 130 min in the propofol trial. MS-222 at 1 g/L immersion was found to reliably produce surgical anesthesia in Sonoran desert toads with a faster onset of action and recovery when compared to propofol administered intracoelomically at 35 mg/kg.