Toxicology

Anticholinergic

Mechanism of toxicity is through competitive antagonism of the effects of acetylcholine at

peripheral muscarinic receptors and central receptors.

ii.

Signs and symptoms include altered mental status, delirium, hallucinations, mumbled

speech, dry mucous membranes, mydriasis, anhidrosis, flushing, hyperthermia, tachycardia,

hypoactive bowel sounds, and urinary retention.

iii.

Common drugs that have anticholinergic activity include antihistamines, antipsychotics,

tricyclic antidepressants, and skeletal muscle relaxants.

Cholinergic

Mechanism of toxicity is inhibition of acetylcholinesterase causing accumulation of

acetylcholine ultimately resulting in overstimulation of muscarinic and nicotinic receptors.

ii.

Signs and symptoms include confusion, central nervous system (CNS) depression, miosis,

wet mucous membranes, salivation, lacrimation, diaphoresis, emesis, urination, diarrhea,

muscle weakness/twitching, bronchospasm, bronchorrhea, hypertension, tachycardia, and

bradycardia.

iii.

Common drugs that have cholinergic activity include organophosphates, nerve agents,

nicotine, pilocarpine, and physostigmine.

Opioid

Mechanism of toxicity is stimulation of opioid receptors causing a decrease in autonomic

activity.

ii.

Signs and symptoms include sedation, miosis, decreased bowel sounds (ileus), respiratory

depression, hypotension, and bradycardia.

iii.

Common drugs that have opioid activity include heroin, morphine, codeine, synthetic opioids,

loperamide, and dextromethorphan (in large quantities).

Mechanism of toxicity is through an increase in sympathetic tone through release of

cathecholamines, inhibition of reuptake, by direct receptor stimulation, and alterations in

neurotransmitter metabolism.

ii.

Signs and symptoms include agitation, delirium, mydriasis, diaphoresis, myoclonus,

hyperthermia, hypertension, and tachycardia.

iii.

Common drugs that have sympathomimetic activity include cocaine, methamphetamine,

pseudoephedrine, and caffeine.

Drug screens are used in acute toxic ingestions, the most common of which is the qualitative urine

screen. This method tests for the presence of a substance, but it cannot detect the amount of substance

present. If a toxin is known, a quantitative drug screen may be used to confirm the exact amount present.

Although urine drug screens may vary by institution, they may include amphetamines, barbiturates,

benzodiazepines, cocaine, MDMA (ecstasy), methamphetamines, opiates, THC (marijuana), and tricyclic

antidepressants (TCAs). Urine screens are not considered comprehensive; therefore, the presence of

additional agents should be tested for (e.g., acetaminophen, salicylates). However, comprehensive drug

screens using gas chromatography and liquid chromatography together with mass spectrometry can be

used in patients presenting with severe or unexplained toxicity.

A negative screen does not exclude the presence of a toxic substance, especially if the presumed

agent is not present on the screen. Many agents are not identified by their designated screen; this is

especially an issue with standard amphetamine, benzodiazepine, and opiate screens.