Atropine and glycopyrrolate significantly raise the heart rate of Sonoran Desert toads (Incilius alvarius).

OBJECTIVE: To evaluate the effects of atropine and glycopyrrolate on the heart rate (HR) of Sonoran Desert toads (Incilius alvarius). METHODS: In part 1, toads received 0.1 mg/kg atropine IM, 0.025 mg/kg glycopyrrolate IM, 0.05 mg/kg glycopyrrolate IM, saline, or negative control in a randomized crossover study. Heart rate was monitored at baseline and 1, 3, 5, 10, 15, 20, 25, 30, 40, 50, and 60 minutes. In part 2, toads received 10 mg/kg alfaxalone IM followed by 0.05 mg/kg glycopyrrolate or saline. Heart rate was monitored at baseline and 1, 3, 5, 10, 15, 20, 25, 30, 40, 50, 60, 80, 100, and 120 minutes. RESULTS: In part 1 (n = 19), all 3 anticholinergic protocols significantly increased the HR between 3 and 15 minutes versus both controls. Atropine significantly increased the HR versus saline between 3 and 30 minutes. Both glycopyrrolate doses significantly increased the HR versus saline at 60 minutes. In part 2 (n = 10), glycopyrrolate significantly increased the HR versus saline at 10 minutes (mean HR difference 6.8 beats/min, SE of the difference 1.467 [95% CI, 1.024 to 12.58]). CONCLUSIONS: Atropine and glycopyrrolate significantly increased the HR in conscious toads, with glycopyrrolate having longer efficacy. The effective period of glycopyrrolate was briefer in alfaxalone-sedated toads. CLINICAL RELEVANCE: Performing safe, effective anesthesia can be challenging in amphibians given their unique physiology. Anticholinergic drugs are commonly used in veterinary medicine to address anesthesia-induced bradycardia. Additional studies are indicated to further evaluate the clinical efficacy of anticholinergics in amphibians.