Atropine and Glycopyrrolate

Introduction^1-3

• Atropine and glycopyrrolate are both competitive, reversible muscarinic acetylcholine receptor antagonists. Blockade of these receptors reduces parasympathetic tone, leading to physiologic patterns resembling sympathetic activation.
• While their actions are similar, structural differences yield distinct systemic profiles: atropine is a naturally occurring, lipid-soluble tertiary amine, whereas glycopyrrolate is a synthetic, poor lipid-soluble quaternary amine.

• Atropine’s lipid solubility allows it to cross the blood-brain barrier, causing CNS effects that are less prominent than those of glycopyrrolate. Atropine also readily crosses the placenta, whereas glycopyrrolate does not. This distinction is clinically relevant when considering whether fetal exposure to anticholinergic effects is desired or should be avoided.

Pharmacokinetics^2,4,5

Mechanism of Action and Systemic Effects³

• The systemic effects of these anticholinergic agents mimic patterns of sympathetic stimulation.
• Atropine has affinity for M4 and M5 receptors, but these do not contribute meaningfully to its clinical profile at therapeutic doses.

Clinical Uses and Common Dosing Recommendations^2,4,5

Relative Contraindications^2,4,6

• Atropine and glycopyrrolate’s strong chronotropic effect pose an increased risk in patients with elevated blood pressure, coronary artery disease, tachyarrhythmias, or congestive heart failure.
• Angle-closure glaucoma: risk of increased intraocular pressure, avoid unless controlled with a miotic agent
• Partial or complete obstructive uropathy, as these medications may worsen obstruction
• Gastrointestinal obstruction or ileus
• Myasthenia gravis- patients with this condition often take cholinergic agonists, and thus administering atropine or glycopyrrolate can mask initial warning signs of cholinergic crisis from overdose.

Overdose and Management^1,7

• Atropine and glycopyrrolate share similar peripheral anticholinergic overdose features- tachycardia, dry mucosa, anhidrosis with hyperthermia, mydriasis, ileus, and urinary retention. The key clinical distinction is CNS involvement.
• Atropine readily crosses the blood-brain barrier, causing central anticholinergic syndrome: agitation, delirium, hallucinations, seizure, and coma.
• Glycopyrrolate poorly crosses the blood-brain barrier, so overdose toxicity produces minimal or no CNS toxicity.
• Hyperthermia results from inhibition of sweating, not increased metabolic rate.
• Management is primarily supportive. Agitated patients can be treated with benzodiazepines, fluids may be given to address hypotension or reduce the risk of rhabdomyolysis, and active cooling should be used if the patient develops significant hyperthermia.
• In severe toxicity (primarily with atropine overdose), physostigmine (an acetylcholinesterase inhibitor) may reverse central symptoms.