Study finds atropine, glycopyrrolate raise heart rate in desert toads

A new study in the American Journal of Veterinary Research reports that atropine and glycopyrrolate significantly raise heart rate in Sonoran Desert toads (Incilius alvarius), offering rare species-specific pharmacology data for a toad that is increasingly relevant in zoological, wildlife, and exotic animal practice. According to the study abstract, investigators evaluated intramuscular atropine and two glycopyrrolate doses in a randomized crossover design, then examined whether glycopyrrolate could reverse or mitigate bradycardia after alfaxalone sedation. (pubmed.ncbi.nlm.nih.gov)

That fills a notable gap. Amphibian anesthesia protocols are often pieced together from small studies, cross-species extrapolation, and clinician experience, even though amphibian responses can be highly species-specific. In Sonoran Desert toads, that need is especially clear: prior work by some of the same research group found that 10 mg/kg IM alfaxalone produced significant transient cardiorespiratory depression in all toads studied, with sedation typically developing within 30 to 40 minutes and adverse effects resolving within the 120-minute observation period. (researchgate.net)

From the abstract provided for the new paper, part 1 compared 0.1 mg/kg atropine IM, 0.025 mg/kg glycopyrrolate IM, 0.05 mg/kg glycopyrrolate IM, saline, and a negative control, with heart rate measured at baseline and multiple time points out to 60 minutes. Part 2 paired 10 mg/kg alfaxalone IM with 0.05 mg/kg glycopyrrolate, directly testing whether the anticholinergic could increase heart rate after anesthetic-associated slowing. Even without the full text, the headline result is straightforward: both atropine and glycopyrrolate significantly increased heart rate in this species. (pubmed.ncbi.nlm.nih.gov)

The pharmacologic direction of effect is not surprising, but the species-specific confirmation matters. In other species, atropine and glycopyrrolate are both muscarinic antagonists used to increase heart rate and reduce secretions, though their potency and rhythm effects can differ. Human anesthesia literature has long shown dose-related heart rate increases with both agents, and some studies have found atropine produces a larger rise in heart rate or more dysrhythmias than glycopyrrolate in certain settings. Those differences are one reason amphibian-specific data are more useful than borrowing expectations from mammals. (openanesthesia.org)

The broader context also helps explain why Sonoran Desert toads are drawing more clinical attention. The species has been the subject of recent work on neurologic examination standards and chemical defense biology, and it is well known in companion animal medicine because exposure can cause severe toxicosis in dogs. A recent canine review described 208 suspected Incilius alvarius exposure cases from Arizona emergency hospitals, while the MSD Veterinary Manual notes that serious poisoning is associated with large toads such as Incilius alvarius and that atropine should not be used until cardiovascular status is assessed. That toxicology context is separate from the new anesthesia study, but it reinforces the importance of understanding this species’ cardiovascular physiology. (pubmed.ncbi.nlm.nih.gov)

Why it matters: For veterinary teams, the study’s value is less about novelty for novelty’s sake and more about decision support. If alfaxalone can depress cardiopulmonary function in Sonoran Desert toads, then knowing that atropine and glycopyrrolate reliably increase heart rate gives clinicians a more evidence-based starting point for anesthetic planning, monitoring, and intervention. That could be relevant for zoo and aquarium medicine, wildlife rehabilitation, academic research colonies, and referral exotics practice. It may also help reduce reliance on cross-species assumptions that don’t always hold in amphibians. (researchgate.net)

There are still limits. The available abstract does not, by itself, provide the full magnitude of effect, adverse event detail, or enough information to determine whether one drug or dose should be preferred in routine practice. And because amphibian cardiovascular responses can vary by species, temperature, hydration status, and handling, clinicians should be cautious about generalizing beyond Incilius alvarius. That said, the study appears to move the field toward more tailored anesthesia protocols in a species where even basic clinical reference points are still being established. This is an inference based on the study design and prior Sonoran Desert toad anesthesia work. (pubmed.ncbi.nlm.nih.gov)

What to watch: The next step is the full paper, especially any data on onset, duration, comparative dose response, rhythm effects, and how glycopyrrolate performed after alfaxalone, because those details are what will determine whether this finding changes day-to-day amphibian anesthesia protocols. (pubmed.ncbi.nlm.nih.gov)