Atropine Flashcards
What is the mechanism of action of atropine?
Atropine is a muscarinic receptor antagonist that competitively inhibits acetylcholine at parasympathetic synapses, leading to anticholinergic effects.
What are the primary indications for atropine?
Used for bradycardia, organophosphate poisoning, mydriasis induction for ophthalmologic exams, and as a pre-anesthetic to reduce secretions.
How does atropine treat bradycardia?
By blocking vagal stimulation of the SA node, increasing heart rate and improving conduction through the AV node.
Why is atropine used in organophosphate poisoning?
Organophosphates cause excessive cholinergic activity by inhibiting acetylcholinesterase; atropine counteracts this by blocking muscarinic receptors.
What is the effect of atropine on the eye?
It causes mydriasis (pupil dilation) and cycloplegia (loss of accommodation) by blocking the parasympathetic control of the iris sphincter and ciliary muscle.
What are the major anticholinergic side effects of atropine?
- Dry mouth
- Constipation
- Urinary retention
- Tachycardia
- Blurred vision
- Confusion
- Hyperthermia
What is the underlying cause for atropine fever (hyperthermia)?
Sweat gland activation is cholinergic but part of the sympathetic nervous system. Eccrine sweat glands (responsible for thermoregulatory sweating) are innervated by sympathetic cholinergic fibers that release acetylcholine (ACh), which acts on muscarinic M3 receptors to stimulate sweating. Atropine inhibits sweating (anhidrosis) because it is a muscarinic receptor antagonist, blocking M3 receptors on sweat glands.
Why does atropine cause dry mouth?
It inhibits salivary gland secretion, reducing saliva production.
How does atropine cause constipation?
By reducing gastrointestinal motility and peristalsis via inhibition of muscarinic receptors in the gut.
Why can atropine cause urinary retention?
It relaxes the detrusor muscle of the bladder and constricts the internal sphincter, making urination more difficult.
Why does atropine cause tachycardia?
It blocks vagal inhibition of the SA node, leading to an increased heart rate.
How does atropine cause confusion and cognitive impairment?
By inhibiting central muscarinic receptors, which can impair memory and cognition, especially in elderly patients.
Why does atropine cause blurred vision?
It induces cycloplegia, preventing the eye from adjusting focus.
Why is atropine contraindicated in glaucoma?
It increases intraocular pressure by blocking aqueous humor outflow.
Why does atropine cause hyperthermia?
It inhibits sweat gland secretion, reducing the body’s ability to dissipate heat.
What is the classic mnemonic for atropine toxicity?
‘Hot as a hare, dry as a bone, red as a beet, blind as a bat, mad as a hatter’.
What are the symptoms of atropine overdose?
Hyperthermia, anhidrosis, dry mouth, tachycardia, flushed skin, mydriasis, urinary retention, hallucinations, and delirium.
How is atropine toxicity treated?
Supportive care and physostigmine, a reversible acetylcholinesterase inhibitor that restores acetylcholine levels.
In which conditions should atropine be used with caution?
Glaucoma, benign prostatic hyperplasia (BPH), elderly patients (risk of cognitive impairment), and tachyarrhythmias.
Why is atropine avoided in elderly patients?
It increases the risk of confusion, delirium, and cognitive impairment due to central anticholinergic effects.
What type of receptors does atropine block?
Muscarinic receptors (M1, M2, M3) but has no effect on nicotinic receptors.
Why is atropine not useful for neuromuscular blockade reversal?
It does not affect nicotinic receptors at the neuromuscular junction.
How does atropine affect respiratory secretions?
It reduces airway secretions, which is why it is used as a pre-anesthetic agent.
How does atropine affect sweat glands?
It inhibits muscarinic receptors in sweat glands, leading to reduced sweating and increased body temperature.
