💊 Atropine

Atropine is an anticholinergic (antimuscarinic) agent, belonging to the class of parasympatholytic drugs. It acts by competitively blocking muscarinic acetylcholine receptors.

Atropine competitively blocks the action of acetylcholine at muscarinic receptors in the heart, smooth muscle, and glands. In the heart, this leads to an increase in sinus rate and AV nodal conduction by inhibiting vagal tone. It also reduces glandular secretions (e.g., saliva, bronchial mucus) and relaxes smooth muscle.

The primary indication for atropine is the treatment of symptomatic bradycardia, particularly in the context of myocardial infarction or vagally mediated bradycardia. It is also used as an antidote for organophosphate poisoning and carbamate poisoning. Additionally, it can be used to reduce excessive salivary and bronchial secretions during surgery or in palliative care.

Absolute contraindications include known hypersensitivity to atropine. Relative contraindications include narrow-angle glaucoma (can precipitate acute angle closure), prostatic hypertrophy (risk of urinary retention), and paralytic ileus (can worsen bowel obstruction). Tachyarrhythmias or unstable angina are also relative contraindications due to the potential to increase heart rate and myocardial oxygen demand.

Common adverse effects are related to its anticholinergic properties and include dry mouth, blurred vision (due to cycloplegia and mydriasis), urinary retention, constipation, and tachycardia. In higher doses, it can cause central nervous system effects such as confusion, delirium, and hallucinations. Skin flushing and hyperthermia (due to inhibition of sweating) can also occur.

When used for bradycardia, continuous ECG monitoring is essential to assess heart rate response. Blood pressure should also be monitored. In cases of organophosphate poisoning, ongoing monitoring of vital signs and neurological status is crucial. For other uses, monitoring for resolution of symptoms and adverse effects is appropriate.

Always confirm patient allergies. Be aware of potential interactions with other anticholinergic drugs (e.g., tricyclic antidepressants, antihistamines) which can potentiate adverse effects. Counsel patients about common side effects like dry mouth and blurred vision, advising caution with driving if vision is affected. In emergency situations, rapid administration is prioritised.

Atropine is a first-line drug for symptomatic bradycardia in advanced life support algorithms. Its effect is to increase heart rate by blocking parasympathetic influence. It is ineffective in cardiac arrest with asystole or pulseless electrical activity (PEA). The anticholinergic side effect profile is important to recognise, especially in older patients.

SBA questions often test the primary indication for symptomatic bradycardia and its mechanism of action (blocking vagal tone). They might also focus on its use as an antidote for organophosphate poisoning. The classic anticholinergic side effects ('red as a beet, dry as a bone, blind as a bat, mad as a hatter, hot as a hare') are frequently tested.