ACMT Toxicology Visual Pearls: Toxic “Weed”

Answer: 1 – Antimuscarinic

Antimuscarinic Toxidrome

This plant is Datura Stramonium, and some common names are jimsonweed, stink weed, locoweed, thornapple, and devil’s trumpet. The plant is a member of the nightshade family. It is an annual, grows worldwide in temperate regions, flowers during summer, and is considered a weed. The leaves, when crushed, produce a distinctive odor, which has been compared to peanut butter. The capsule is spiked, divided into 4 chambers, and contains small, black seeds.¹ These seeds can be intentionally ingested, smoked, or brewed into a tea to produce hallucinations.

Toxicity occurs from blocking the action of acetylcholine by competitive antagonism at muscarinic receptor sites, resulting in an antimuscarinic toxidrome.²

Common signs include:

• Dry flushed skin
• Mydriasis
• Hyperthermia
• Dry mucous membranes
• Tachycardia
• Hypertension
• Bladder distention
• Decreased bowel sounds
• Mental status changes (e.g., confusion, agitation, hallucinations)

Other agents that can produce the antimuscarinic toxidrome include³:

• Antihistamines
• Antipsychotics
• Antispasmodics
• Cyclic antidepressants
• OTC sleep aids
• (Some) muscle relaxants
• Mydriatics

Antimuscarinic Toxicity: Bedside Pearls

Differentiation from Sympathomimetic Toxidrome

The sympathomimetic and antimuscarinic toxidromes can present similarly, and are sometimes mistaken for each other by clinicians. While a decrease in bowel sounds occurs with antimuscarinic toxidrome, this finding can be difficult to discern.

The best way to differentiate antimuscarinic from sympathomimetic toxidromes is by examining the skin:

Diagnostic Trial of Physostigmine

Administration of the antidote, physostigmine, is a rapid method to confirm the diagnosis of antimuscarinic toxidrome. Physostigmine is a short-acting, reversible inhibitor of acetylcholinesterase. The antidote controls agitation in up to 87% and reverses delirium in 96% of patients with pure antimuscarinic toxicity.⁴ Its effects are noted within minutes and last approximately 1 hour. Temporary reversal of delirium may be diagnostic and thereby preclude the need for further testing, including brain imaging and lumbar puncture.

The initial dose is 0.5-1 mg in adults and 0.01-0.02 mg/kg (maximum 0.5 mg) in children, and should be administered IV over 5 minutes.⁴

Physostigmine should not be used in the presence of:

• Asthma
• Gangrene
• Cardiovascular disease
• Mechanical obstruction of the intestine or GU tract
• Any vagotonic state

Adverse effects include cholinergic symptoms:

• Diarrhea and vomiting
• Bronchorrhea
• Seizures

Physostigmine may prolong the activity of depolarizing neuromuscular agents such as succinylcholine. Ventricular arrhythmias and asystole have been reported when administered to patients with sodium channel blockade after cyclic antidepressant overdose.^5,6