Atropine
A competitive muscarinic blocker from belladonna, used for slow heart rate, organophosphate poisoning, drying secretions and dilating the pupil.
Drug card
- Class
- Antimuscarinic
- How it works
- Blocking muscarinic receptors, so parasympathetic effects are switched off
- Used for
- Symptomatic slow heart rate
- Organophosphate, carbamate or mushroom poisoning
- Drying saliva and airway secretions in anesthesia
- Dilating the pupil and relaxing focus for eye exams
- Known for
- Dry mouth
- Fast heart rate
- Blurred vision and sensitivity to light
- Its name
- -trop- means an atropine-like antimuscarinic
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does atropine work?
A tertiary-amine alkaloid that competitively blocks muscarinic receptors on the heart, glands and smooth muscle, so a large enough rise in acetylcholine can overcome it. Removing vagal tone at the SA and AV nodes speeds the heart, and blocking glands dries secretions. It enters the brain, so toxic doses cause restlessness, delirium and hallucinations.
Like other antimuscarinics: They occupy muscarinic acetylcholine receptors without activating them, competitively blocking the acetylcholine released by parasympathetic nerves. The heart speeds up, glands dry up, the smooth muscle of the gut, bladder and airways relaxes, and the pupil dilates and stops focusing. Tertiary amines such as atropine enter the brain; quaternary ones such as hyoscine butylbromide do not.
Uses
What is atropine used for?
- Symptomatic slow heart rate
- Organophosphate, carbamate or mushroom poisoning
- Drying saliva and airway secretions in anesthesia
- Dilating the pupil and relaxing focus for eye exams
Side effects
Side effects of atropine
- Dry mouthKnown for
- Fast heart rateKnown for
- Blurred vision and sensitivity to lightKnown for
- Constipation
- Difficulty passing urine
- Heat intolerance from loss of sweating
- Red, flushed face and neck
- Restlessness and delirium at high dosesSerious
- Hallucinations in overdoseSerious
- Acute angle-closure glaucomaSerious
- Eye stinging and pain (eye drops)
- Allergic reactions, including anaphylaxisSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Ischemic heart disease: the faster rate raises the heart's oxygen demand and can worsen ischemia.
- It can precipitate acute glaucoma.
- Enlarged prostate: complete urinary retention; partial pyloric stenosis can become a full obstruction.
- Chronic lung disease: thickened bronchial secretions can form plugs.
Good to know: The antidote for the muscarinic effects of organophosphate poisoning. Small doses can briefly slow the heart before the typical speeding begins.
Remember it
A way to remember it
Hot as a hare, dry as a bone, red as a beet, blind as a bat, full as a flask.
The classic signs of too much antimuscarinic effect: overheating because sweating stops, a dry mouth and skin, flushing, blurred vision from a wide pupil that cannot focus, and a full bladder from urinary retention. Confusion often comes with them.
A mnemonic widely used in teaching
Its name
-trop- means atropine-like antimuscarinic
Marks atropine relatives. Ipratropium and tiotropium add -ium: as quaternary ammonium compounds they are barely absorbed and act in the airways. Somatropin, a growth hormone, fits by chance.
- Every drug name stem
Its class
Antimuscarinics
Other antimuscarinics with a card:
Easily mixed up with direct-acting muscarinic agonists, anticholinesterases and beta-3 agonists.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Atropine sulfate injection: label (DailyMed)
- Atropine sulfate ophthalmic solution 1%: label (DailyMed)
- Atropine (NCI Thesaurus)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Autonomic nervous system
Atropine is one of 10 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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