January 10, 2026
Botulism has been in the news lately. Currently there are 37 known cases of infantile botulism associated with infant formula.1 MMWR just reported three cases of severe botulism from unlicensed, self-administered cosmetic use.2 One of the characteristics of acute botulism is its "mixed" picture with both antimuscarinic and antinicotinic effects.
Botulinum toxin enters cholinergic presynaptic peripheral nerve terminals. Part of the toxin is a metalloprotease that is specific to the SNARE proteins, resulting in cleavage. The disabled SNARE proteins prevents docking acetylcholine (Ach) vesicles for release into the synapse, thus achieving a presynaptic "blockade" of Ach release.3 This effect at peripheral nerve junctions affects both peripheral cholinergic neurons: nicotinic and muscarinic. Thus, botulinum poisoning results in a peripheral anticholinergic toxidrome e.g. floppy (antinicotinic) and constipated (antimuscarinic) baby; ptosis (antinicotinic) and fixed pupils (antimuscarinic).
In contrast, most xenobiotics labeled as "anticholinergic" act only at the muscarinic receptors and have no effect at nicotinic receptors. The clinical findings associated with poisoning from these xenobiotics are consistent with an antimuscarinic toxidrome, without antinicotinic clinical findings. Additionally, most antimuscarinic pharmaceutical agents cross the blood brain barrier (BBB), causing central antimuscarinic effects like delirium and elevated body temperature. Botulinum toxin does not cross the BBB and thus botulinum poisoned patients do not manifest altered mental status (in the absence of respiratory failure) or "fever".
Keep a level of suspicion for botulinum poisoning when a patient presents with peripheral anticholinergic (antimuscarinic and antinicotinic) effects.
Saralyn R. Williams, MD, Professor of Emergency Medicine, Medicine, and Pediatrics
References
- https://www.fda.gov/food/outbreaks-foodborne-illness/outbreak-investiga…, accessed November 30, 2025.
- Lamere L, Cope J. Beazu R, et al. Severe illnesses after self-injection of botulinum toxin purchased online-New York, Texas, and Wisconsin, 2025 MMWR 2025; 74: 593-96.
- Rummel A. The long journey of botulinum neurotoxins into the synapse. Toxicon 2015;107: 9-24.