Cholinergic Antagonists: Muscarinic and Nicotinic Blocking Drugs

Cholinergic antagonists reduce acetylcholine action. Most clinically familiar medicines are antimuscarinics, used for bradycardia, poisoning, bronchodilation, eye examination, bladder disease, motion sickness and drug-induced movement disorders. Nicotinic antagonists include neuromuscular blockers used during anaesthesia and airway management. They can be lifesaving, but their predictable toxicity—delirium, hyperthermia, urinary retention, bronchospasm, paralysis or apnoea—must be anticipated. This chapter gives common adult teaching doses only: verify indication, formulation, patient factors and current local protocol before prescribing.

Learning outcomes

Link muscarinic receptor blockade to organ effects and toxidrome findings.
Use separate drug knowledge—mechanism, common dose, indication, adverse effects, contraindications, interactions and counselling—for each major agent.
Recognise anticholinergic toxicity and when expert-supervised physostigmine may be appropriate.
Explain that neuromuscular blockers cause paralysis only: they do not provide analgesia, amnesia or unconsciousness.

1. What muscarinic blockade does

Site/receptor	Normal ACh effect	Effect of antagonism	Clinical consequence
M₂, heart	Vagal slowing of SA node and AV conduction.	Increased rate and AV conduction.	Atropine may treat vagal bradycardia; tachyarrhythmia risk.
M₃, glands/airway	Saliva, tears, sweat and bronchial secretion; bronchoconstriction.	Drying and bronchodilation.	Useful before anaesthesia/COPD; dry mouth, thick sputum and heat intolerance.
M₃, eye	Miosis and accommodation for near vision.	Mydriasis and cycloplegia.	Useful for examination; blurred vision and possible acute angle closure.
M₃, gut/bladder	Peristalsis and detrusor contraction.	Reduced gut and bladder contraction.	Useful in overactive bladder; constipation, ileus and urinary retention.
CNS	Cholinergic attention/memory pathways.	Variable, greatest with tertiary amines crossing BBB.	Sedation, impaired memory, agitation or delirium.

Anticholinergic toxidrome: act on the physiology

Dry: dry mouth, absent sweating, dry warm skin, reduced bowel sounds and urinary retention.
Blind: dilated pupils, blurred near vision, photophobia; acute angle closure may present with eye pain/red eye.
Hot/red/fast: hyperthermia, flushing, tachycardia and hypertension may occur.
Confused: agitation, hallucinations, delirium, seizures or coma, especially with CNS-penetrant agents.
Initial management: stop culprit medicines; ABC, ECG, temperature and glucose; treat agitation/seizures and hyperthermia; obtain toxicology help. Physostigmine is reserved for selected severe confirmed central toxicity with continuous monitoring.

2. Classification

Systemic antimuscarinics

Atropine: bradycardia and cholinergic poisoning.
Glycopyrrolate: secretion control and peri-operative co-medication.
Hyoscine (scopolamine): motion sickness/secretions.

Organ-selective use

Ipratropium, tiotropium: inhaled bronchodilation.
Oxybutynin, solifenacin: overactive bladder.
Tropicamide, cyclopentolate: ophthalmic mydriasis/cycloplegia.
Benztropine/procyclidine: selected extrapyramidal reactions.

Nicotinic blockade

Rocuronium, vecuronium, cisatracurium: non-depolarising N_M blockers.
Succinylcholine: depolarising N_M blocker.
Ganglion blockers are largely historical due to widespread autonomic adverse effects.

3. Individual antimuscarinic drug cards

Atropine

Mechanism and receptor profile

Competitive, reversible muscarinic antagonist with central and peripheral activity.
Blocks vagal M₂ effects in the heart and M₃-mediated secretions, bronchial tone, pupil constriction and smooth-muscle contraction.

Formulations and common adult teaching doses

IV/IM/SC injection and ophthalmic preparations exist; doses differ substantially by indication.
For symptomatic adult bradycardia, a common resuscitation teaching regimen is 1 mg IV, repeated every 3–5 minutes to a maximum 3 mg according to current ALS/local protocol.
For organophosphate poisoning, give repeated escalating doses titrated to drying of bronchial secretions and adequate ventilation, not to pupil size or heart rate; follow toxicology protocol.

Indications

Selected symptomatic bradycardia due to vagal excess or AV nodal block when the algorithm indicates it.
Life-threatening muscarinic manifestations of organophosphate/carbamate or muscarinic-mushroom poisoning.
Reduction of secretions/peri-operative vagal bradycardia and selected ophthalmic uses.

Common side effects

Dry mouth and thirst: salivary secretion is reduced.
Blurred near vision/photophobia: mydriasis and cycloplegia impair accommodation.
Tachycardia/palpitations: vagal restraint on the SA node is blocked.
Constipation and urinary hesitancy: gut and detrusor contraction are reduced.

Serious adverse effects

Acute angle-closure glaucoma: pupil dilation can obstruct aqueous drainage in a susceptible eye.
Delirium, hallucinations or hyperthermia: particularly with high systemic exposure and in older adults.
Myocardial ischaemia/tachyarrhythmia: excessive heart-rate increase raises oxygen demand in coronary disease.

Contraindications and cautions

In a true life-threatening poisoning or bradycardic emergency, there may be no absolute contraindication; weigh risk against immediate benefit.
Use caution in narrow-angle glaucoma, prostatic obstruction/urinary retention, pyloric obstruction/ileus, severe ulcerative colitis, fever and coronary disease.
Atropine may not be effective in transplanted-heart bradycardia; prepare alternative pacing/vasoactive strategies.

Interactions

Antihistamines, TCAs, antipsychotics, antiparkinsonian drugs and many bladder medicines add anticholinergic burden.
Anticholinesterases/cholinomimetics oppose the effect; this is used deliberately in selected anaesthetic/toxicology situations.

Monitoring and counselling

Monitor ECG, BP, perfusion, secretions, ventilation, temperature, pupils, urine output and mental state.
In poisoning, airway suction and oxygenation are not optional: atropine does not reverse nicotinic weakness or replace ventilation.

Glycopyrrolate (glycopyrronium)

Mechanism and receptor profile

Quaternary antimuscarinic that acts predominantly peripherally and has limited BBB penetration.
Reduces airway/salivary secretions, blocks vagal bradycardia and counteracts muscarinic effects of neostigmine.

Formulations and common adult teaching doses

Injection, oral and inhaled products exist; dosing depends greatly on indication.
With neostigmine reversal, a commonly taught IV dose is 0.2 mg glycopyrrolate per 1 mg neostigmine, administered together or beforehand under anaesthesia protocol.
For peri-operative secretion control, typical adult doses are 0.1–0.2 mg IV/IM, titrated by the clinician.

Indications

Reduction of secretions and prevention/treatment of peri-operative vagal bradycardia.
Co-administration with neostigmine for reversal of non-depolarising neuromuscular blockade.
Inhaled long-acting products may be used in COPD according to local availability.

Common side effects

Dry mouth and thick secretions: glandular M₃ blockade.
Constipation and urinary retention: reduced gut/detrusor smooth-muscle activity.
Tachycardia: vagal blockade at the heart.

Serious adverse effects

Heat intolerance/hyperthermia: impaired sweating, especially in a febrile or hot environment.
Glaucoma or urinary retention: potentially serious consequences in susceptible patients.

Contraindications and cautions

Caution in angle-closure glaucoma, obstructive uropathy, paralytic ileus, severe ulcerative colitis and tachyarrhythmia.
Limited CNS entry may reduce delirium risk but does not eliminate peripheral toxicity.

Interactions

Additive toxicity occurs with other antimuscarinics.
It deliberately antagonises neostigmine’s muscarinic effects but not its NMJ reversal effect.

Monitoring and counselling

Monitor pulse, secretions, airway patency, bladder function and bowel activity.
During reversal, verify objective recovery of neuromuscular function and adequate ventilation—not just a dry mouth or faster pulse.

Hyoscine (scopolamine)

Mechanism and receptor profile

Tertiary antimuscarinic that crosses the BBB; blocks vestibular and vomiting-pathway cholinergic signalling.
CNS penetration explains motion-sickness benefit and the risk of sedation, confusion and delirium.

Formulations and common adult teaching doses

Transdermal patch, oral and injectable products depend on local availability.
A common motion-sickness patch delivers 1.5 mg over 72 hours, applied behind the ear before travel; use product-specific timing and replacement instructions.

Indications

Prevention of motion sickness and postoperative nausea/vomiting in selected patients.
Selected palliative-care secretion reduction under specialist direction.

Common side effects

Dry mouth: reduced salivary secretion.
Drowsiness and blurred vision: central action plus cycloplegia/mydriasis.
Constipation and urinary hesitancy: smooth-muscle blockade.

Serious adverse effects

Delirium, agitation or hallucinations: more likely in older adults or with excess exposure.
Acute angle closure or urinary retention: can require emergency care.
Hyperthermia: sweat suppression impairs heat dissipation.

Contraindications and cautions

Avoid or use specialist caution in narrow-angle glaucoma, urinary retention, bowel obstruction, myasthenia gravis and dementia.
Older adults are particularly vulnerable to falls and confusion.

Interactions

Alcohol, sedatives and CNS-active medicines increase impairment.
Other anticholinergics markedly increase delirium, constipation and retention risk.

Monitoring and counselling

Wash hands after handling a patch; avoid touching eyes because accidental ocular transfer may dilate a pupil.
Do not drive or operate machinery until personal response is known; seek help for confusion, eye pain or inability to pass urine.

Ipratropium

Mechanism and receptor profile

Quaternary inhaled antimuscarinic; blocks M₃-mediated vagal bronchoconstriction and mucus secretion with little CNS entry.
Short-acting muscarinic antagonist (SAMA), usually used as an adjunct bronchodilator rather than sole emergency treatment.

Formulations and common adult teaching doses

Metered-dose inhaler and nebuliser solution.
A common nebulised adult dose is 500 micrograms every 6–8 hours (often 3–4 times daily); severe acute asthma/COPD pathways may use repeated doses combined with salbutamol according to local protocol.

Indications

Maintenance bronchodilation in COPD.
Adjunct to inhaled beta₂ agonist in severe acute asthma or COPD exacerbation according to guideline.

Common side effects

Dry mouth and throat irritation: local antimuscarinic action.
Cough or unpleasant taste: inhalation-related effects.
Headache: reported in some patients.

Serious adverse effects

Paradoxical bronchospasm: rare worsening of wheeze immediately after inhalation; stop and treat urgently.
Acute narrow-angle glaucoma: aerosol reaching the eye may cause mydriasis, eye pain/redness and visual halos.
Urinary retention/tachyarrhythmia: uncommon but important in susceptible patients.

Contraindications and cautions

Caution in narrow-angle glaucoma, prostatic enlargement/bladder-neck obstruction and prior hypersensitivity to ipratropium/related products.
It is not a substitute for oxygen, systemic therapy or ventilation in severe respiratory failure.

Interactions

Avoid duplicate antimuscarinic inhalers unless deliberately prescribed; cumulative dry mouth/retention may occur.
Often combined with salbutamol in a nebuliser when local compatibility/timing guidance is followed.

Monitoring and counselling

Assess inhaler technique, symptom relief, peak-flow/spirometry where relevant, pulse, urine symptoms and eye exposure.
Keep mask/aerosol out of the eyes and seek help for sudden worsening wheeze, eye pain or inability to urinate.

Tiotropium

Mechanism and receptor profile

Long-acting inhaled muscarinic antagonist (LAMA), with prolonged M₃ blockade in airway smooth muscle.
Produces sustained bronchodilation; it is a maintenance medicine, not acute rescue therapy.

Formulations and common adult teaching doses

Dry-powder capsule inhaler and soft-mist inhaler formulations differ.
A common dry-powder COPD regimen is 18 micrograms inhaled once daily; soft-mist dose depends on device/indication. The capsule must be inhaled with its device, not swallowed.

Indications

Maintenance treatment of COPD.
Maintenance add-on treatment of asthma in selected patients and age groups where locally indicated.

Common side effects

Dry mouth: the most characteristic effect.
Pharyngitis, cough or sinus symptoms: may occur with inhaled use.
Constipation: systemic antimuscarinic effect in some patients.

Serious adverse effects

Paradoxical bronchospasm: stop and treat as an acute airway reaction.
Acute angle closure: eye exposure can trigger painful red eye/blurred vision.
Urinary retention/hypersensitivity: consider urgently if reduced urine output, facial swelling or severe rash occurs.

Contraindications and cautions

Contraindicated in known hypersensitivity to tiotropium/ipratropium or components.
Use caution in narrow-angle glaucoma, prostatic hyperplasia/bladder-neck obstruction and renal impairment where systemic exposure may rise.

Interactions

Minimise unnecessary co-prescribing with other anticholinergics.
It may be used with other COPD maintenance therapies as guideline-directed, but is not an alternative to a rapid-acting rescue bronchodilator.

Monitoring and counselling

Check device-specific technique and adherence; assess exacerbations, rescue use, urine symptoms and eye symptoms.
Do not use for a sudden attack—use the prescribed rapid-acting reliever and escalate care when necessary.

Oxybutynin

Mechanism and receptor profile

Antimuscarinic with relative M₃ effect on detrusor smooth muscle; reduces involuntary bladder contractions.
Crosses the BBB, so cognitive and CNS effects are clinically important.

Formulations and common adult teaching doses

Immediate-release tablets/liquid, modified-release tablets and transdermal patch/gel exist.
Immediate-release commonly begins at 2.5–5 mg two or three times daily; extended-release commonly starts 5–10 mg once daily. Titrate with product limits and patient tolerance.

Indications

Overactive bladder with urgency, frequency and urge incontinence.
Selected neurogenic detrusor overactivity under specialist care.

Common side effects

Dry mouth: often dose-limiting.
Constipation: reduced gut motility.
Blurred vision: reduced accommodation.
Drowsiness/confusion: CNS penetration can impair cognition, especially in older people.

Serious adverse effects

Urinary retention: bladder relaxation can become excessive, especially with outlet obstruction.
Heat exhaustion/hyperthermia: reduced sweating impairs cooling.
Acute angle closure or delirium: require prompt evaluation.

Contraindications and cautions

Avoid in urinary retention, gastric retention, uncontrolled narrow-angle glaucoma and known obstructive GI disease.
Use cautiously in frail older adults, dementia, severe constipation, BPH and high anticholinergic burden.

Interactions

Other antimuscarinics, sedating antihistamines, TCAs and antipsychotics add cognitive/retention burden.
Strong CYP3A4 inhibitors can raise exposure to certain formulations; check the product.

Monitoring and counselling

Review bladder diary, urgency/incontinence response, post-void residual when indicated, constipation, cognition, falls and dry mouth.
Use bladder training and fluid/caffeine advice alongside medicine; report inability to pass urine, severe constipation, confusion or eye pain.

Solifenacin

Mechanism and receptor profile

Relatively M₃-selective antimuscarinic used to reduce detrusor overactivity.
Relative selectivity does not remove the risks of dry mouth, constipation, retention or glaucoma.

Formulation and common adult teaching dose

Oral once-daily tablets.
Commonly start 5 mg once daily, with increase to 10 mg once daily if appropriate; reduce/avoid in significant renal/hepatic impairment according to product guidance.

Indications

Overactive bladder with urgency, frequency and urge urinary incontinence.

Common side effects

Dry mouth: common dose-related effect.
Constipation/dyspepsia: reduced GI motility.
Blurred vision: accommodation impairment.

Serious adverse effects

Urinary retention: especially with bladder-outlet obstruction.
Severe constipation/faecal impaction or ileus: possible in susceptible patients.
QT prolongation risk: use caution in patients with known QT risk or interacting drugs.

Contraindications and cautions

Avoid in urinary retention, gastric retention and uncontrolled narrow-angle glaucoma.
Review renal/hepatic function, constipation history, QT risk and cognitive vulnerability.

Interactions

Strong CYP3A4 inhibitors can substantially increase exposure; dose limits apply.
Other anticholinergic medicines increase toxicity; QT-prolonging medicines may add arrhythmia risk.

Monitoring and counselling

Assess symptom benefit after several weeks, bowel function, residual urine when needed and anticholinergic burden.
Report palpitations/syncope, severe constipation, eye pain or inability to void.

Tropicamide and cyclopentolate

Mechanism and receptor profile

Short-acting topical antimuscarinics that cause mydriasis; cyclopentolate produces more cycloplegia for refraction.
They block parasympathetic iris-sphincter and ciliary-muscle effects.

Formulations and common adult teaching doses

Tropicamide: commonly 0.5–1% ophthalmic drops, 1 drop and repeat as ophthalmology directs.
Cyclopentolate: commonly 0.5–1% ophthalmic drops for cycloplegic refraction; dosing is age- and procedure-specific.

Indications

Pupil dilation for fundus examination; cycloplegia for refraction.
Use in uveitis only under ophthalmology direction, often with additional treatment.

Common side effects

Photophobia and blurred near vision: enlarged pupil and loss of accommodation.
Stinging/redness: local ocular irritation.
Dry mouth/flushing: possible systemic absorption effects.

Serious adverse effects

Acute angle-closure glaucoma: painful red eye, headache, nausea, halos and reduced vision require emergency review.
Anticholinergic CNS toxicity: agitation/confusion may occur, especially in children or with excessive dosing.

Contraindications and cautions

Screen for narrow anterior chamber/angle-closure risk and previous angle closure; ophthalmology decides when dilation is safe.
Extra care in infants/children and older adults because systemic effects may be larger.

Interactions

Other anticholinergics increase systemic effects.
Use caution with adrenergic mydriatics because combined dilation can raise angle-closure risk in susceptible eyes.

Monitoring and counselling

Use punctal occlusion where taught to reduce systemic absorption.
Do not drive until vision clears; wear sunglasses and seek urgent care for painful red eye or sudden vision loss.

Benztropine and procyclidine

Mechanism and receptor profile

Central antimuscarinics used to restore acetylcholine–dopamine balance in selected drug-induced extrapyramidal symptoms (EPS).
They reduce tremor/rigidity from acute dystonia or drug-induced parkinsonism, but do not treat tardive dyskinesia and may worsen cognition.

Formulations and common adult teaching doses

Benztropine: oral 0.5–2 mg once or twice daily; for acute dystonia, specialist protocols may use 1–2 mg IM/IV.
Procyclidine: oral 2.5–5 mg two or three times daily is a typical starting pattern; acute IM/IV regimens are protocol-based.

Indications

Acute dystonic reactions due to dopamine-blocking medicines.
Selected drug-induced parkinsonism when medicine review/reduction is insufficient or not possible.

Common side effects

Dry mouth and constipation: peripheral antimuscarinic effects.
Blurred vision and urinary hesitancy: accommodation/detrusor effects.
Memory difficulty/sedation: CNS penetration is clinically relevant.

Serious adverse effects

Delirium/hallucinations: especially in older adults or with high doses/polypharmacy.
Hyperthermia, ileus or urinary retention: antimuscarinic emergency complications.
Worsening tardive dyskinesia: do not use as routine treatment for tardive syndromes.

Contraindications and cautions

Avoid/caution in narrow-angle glaucoma, urinary retention, bowel obstruction, myasthenia gravis, dementia and frailty.
Regularly reassess need; avoid indefinite prophylaxis unless there is a clear specialist reason.

Interactions

Antipsychotics with anticholinergic properties, sedating antihistamines and TCAs add delirium/retention risk.
Alcohol and sedatives increase impaired coordination and falls.

Monitoring and counselling

Document the EPS phenotype, onset, offending medicine and response; address the cause where possible.
Report confusion, fever, constipation, eye pain or inability to void; avoid driving if sedated or visually blurred.

4. Nicotinic antagonists: individual anaesthetic drug cards

Non-negotiable safety rule

Neuromuscular blockers cause paralysis only. They do not sedate, provide analgesia or cause amnesia.
Give only by trained teams with pre-oxygenation, airway equipment, continuous monitoring, a ventilation plan and adequate induction/sedation/analgesia.
Use objective neuromuscular monitoring (e.g., train-of-four) and document recovery before extubation.

Rocuronium

Mechanism and receptor profile

Non-depolarising competitive antagonist at nicotinic N_M receptors at the neuromuscular junction.
Prevents ACh-driven end-plate depolarisation, causing skeletal-muscle paralysis with no effect on consciousness.

Formulation and common adult teaching dose

IV injection only in anaesthesia/critical-care settings.
Routine intubation commonly uses 0.6 mg/kg IV; rapid-sequence protocols may use higher doses (often 1–1.2 mg/kg) according to clinician and local airway pathway. Maintenance/infusion regimens are monitored and individualised.

Indications

Facilitation of tracheal intubation, skeletal-muscle relaxation during surgery and controlled ventilation.

Common side effects

Prolonged weakness: effect lasts longer with higher dose, organ dysfunction or interacting drugs.
Injection-site discomfort: may occur during administration.

Serious adverse effects

Apnoea/awareness while paralysed: catastrophic if ventilation and adequate anaesthesia are not ensured.
Anaphylaxis: neuromuscular blockers are recognised peri-operative allergy triggers.
Residual paralysis after surgery: can cause airway obstruction, aspiration and hypoventilation.

Contraindications and cautions

Contraindicated in known hypersensitivity; use caution in neuromuscular disease, severe hepatic dysfunction, electrolyte disturbance, hypothermia and major burns.
Always prepare for difficult airway and failed-intubation sequence before giving paralysis.

Interactions

Volatile anaesthetics, aminoglycosides, magnesium, lithium and some antiarrhythmics may potentiate blockade.
Reversal options depend on agent, depth of block and local availability; neostigmine and sugammadex have distinct indications and monitoring needs.

Monitoring and counselling

Continuous ventilation, capnography, oxygenation, haemodynamics and objective neuromuscular monitoring are required.
Before extubation, verify sustained recovery and clinical airway strength rather than relying on elapsed time.

Vecuronium

Mechanism and receptor profile

Non-depolarising competitive N_M antagonist with minimal cardiovascular effect in many patients.
Like all NMJ blockers, produces paralysis without sedation or analgesia.

Formulation and common adult teaching dose

IV injection; a typical intubation teaching dose is 0.08–0.1 mg/kg IV, with maintenance doses/infusions titrated to nerve stimulation and clinical context.

Indications

Adjunct to general anaesthesia for intubation, surgery and mechanical ventilation.

Common side effects

Prolonged paralysis: particularly with renal/hepatic dysfunction, critical illness or potentiating medicines.
Injection-related discomfort: uncommon but possible.

Serious adverse effects

Apnoea/ventilator dependence: expected if given, unsafe without controlled ventilation.
Residual block and aspiration: can occur if recovery is not objectively confirmed.
Anaphylaxis: rare but life-threatening.

Contraindications and cautions

Known hypersensitivity, neuromuscular disorders, significant organ impairment, electrolyte imbalance, hypothermia and burns need specialist planning.
Never use to “calm” an agitated patient without appropriate sedation, analgesia and airway competence.

Interactions

Aminoglycosides, magnesium, lithium, local anaesthetics and volatile agents can intensify/extend block.
Corticosteroids plus prolonged ICU paralysis may contribute to critical-illness weakness; reassess daily.

Monitoring and counselling

Use train-of-four and full anaesthetic/ventilation monitoring.
Plan reversal/recovery before administration, including post-operative respiratory support when required.

Cisatracurium

Mechanism and receptor profile

Non-depolarising competitive N_M antagonist; broken down largely by Hofmann elimination/ester hydrolysis, making clearance relatively less dependent on kidney/liver function.
Often chosen when histamine release or organ dysfunction is a concern, though it still requires full paralysis precautions.

Formulation and common adult teaching dose

IV injection/infusion. A common intubation dose is 0.15–0.2 mg/kg IV; maintenance/ICU infusion requires protocol-based titration to objective monitoring.

Indications

Facilitation of intubation/surgery and selected mechanically ventilated critical-care patients under specialist protocol.

Common side effects

Prolonged weakness: may still occur in critical illness, hypothermia, acidosis or drug interactions.
Flushing/hypotension: less histamine release than atracurium but haemodynamic effects remain possible.

Serious adverse effects

Apnoea and awareness if inadequately sedated: same fundamental risk as all paralytics.
Anaphylaxis: possible with all neuromuscular blockers.
ICU-acquired weakness: prolonged administration requires daily review of ongoing need.

Contraindications and cautions

Hypersensitivity, neuromuscular disease and failure to provide ventilation/sedation are critical concerns.
Acid–base disturbance and hypothermia can alter duration; do not assume “organ independent” means risk-free.

Interactions

Magnesium, aminoglycosides, lithium, volatile anaesthetics and other neuromuscular effects may potentiate blockade.
Other paralytics should not be duplicated without an anaesthetic plan.

Monitoring and counselling

Monitor TOF, capnography, ventilation, sedation/analgesia, temperature and haemodynamics.
Use the minimum effective duration and document recovery prior to extubation.

Succinylcholine (suxamethonium)

Mechanism and receptor profile

Depolarising N_M agonist: initially depolarises the motor end plate (fasciculations), then produces persistent depolarisation and flaccid paralysis.
Very rapid onset and short duration in normal pseudocholinesterase activity make it useful for selected rapid-sequence intubation.

Formulation and common adult teaching dose

IV injection. A common adult intubation teaching dose is 1–1.5 mg/kg IV; actual choice depends on airway, contraindications and local RSI protocol.

Indications

Facilitation of rapid-sequence intubation and brief procedures requiring rapid onset, when not contraindicated.

Common side effects

Fasciculations and postoperative myalgia: initial depolarisation of skeletal muscle.
Transient bradycardia: more likely with repeat doses, children or vagal stimulation.
Increased intraocular/intragastric pressure: may be clinically relevant in selected patients.

Serious adverse effects

Hyperkalaemic cardiac arrest: high risk in major burns/crush injury, denervation, neuromuscular disease and prolonged immobilisation after the risk period develops.
Malignant hyperthermia: hypercapnia, muscle rigidity and rapidly rising temperature require immediate dantrolene-based emergency protocol.
Prolonged apnoea: pseudocholinesterase deficiency or inhibition can greatly extend paralysis.
Anaphylaxis: possible peri-operative emergency.

Contraindications and cautions

Avoid in known susceptibility to malignant hyperthermia, hyperkalaemia, pseudocholinesterase deficiency and conditions with up-regulated extrajunctional receptors (e.g., certain burns, denervation and neuromuscular disorders).
Use only with immediate airway/ventilation capability and adequate induction/sedation.

Interactions

Potassium-raising states/drugs increase hyperkalaemia danger.
Cholinesterase inhibitors and organophosphates may prolong effect; some anaesthetic medicines potentiate bradycardia or malignant-hyperthermia risk.

Monitoring and counselling

Check history for burns, paralysis/immobility, muscle disease, family anaesthetic problems and potassium abnormalities before use when time allows.
Continuously monitor ECG, oxygenation, capnography, temperature and neuromuscular recovery; prepare alternative paralytic if contraindicated.

5. Safer prescribing: high-risk patients and interactions

Situation	Why it matters	Practical safeguard
Older adult, dementia or falls	Cumulative anticholinergic burden worsens cognition, constipation, retention and falls.	Review all medicines; choose non-drug or lower-burden options and reassess benefit.
Glaucoma/BPH/constipation	Antimuscarinic effects can precipitate angle closure, retention or ileus.	Screen before prescribing; explain red flags and arrange review.
Severe asthma/COPD exacerbation	Inhaled antimuscarinic is an adjunct; it does not replace rescue bronchodilator, steroids, oxygen or ventilation.	Use the local acute-airway pathway and reassess response promptly.
Neuromuscular blocker use	Paralysis, awareness and residual block can be fatal.	Full airway/sedation/ventilation plan, TOF monitoring and recovery documentation.
Multiple anticholinergics	Toxicity is additive even when each product seems modest alone.	Check OTC sleep/allergy medicines, psychotropics, bladder drugs and eye drops.

Physostigmine in anticholinergic toxicity: specialist decision

Potential role: severe, confirmed central antimuscarinic delirium in a monitored setting after toxicology assessment.
Do not use blindly: exclude important conduction delay, suspected tricyclic-antidepressant toxicity, seizure risk and mixed/uncertain overdoses.
Give only with: continuous ECG, resuscitation equipment, staff able to treat bradycardia/seizure/bronchospasm and a protocol-directed slow IV dose.
Supportive care remains essential: airway, cooling, fluids, agitation control and treatment of complications cannot be replaced by an antidote.

6. OSCE and ward-round checklist

Identify the target: bradycardia, secretions, bronchoconstriction, overactive bladder, eye examination, EPS or paralysis for airway management.
Screen before giving: glaucoma, prostatic obstruction/retention, constipation/ileus, dementia/falls, heart disease, airway status, renal/hepatic function and complete medicines list.
Explain expected effects: dry mouth, blurry near vision, constipation, urine difficulty and impaired heat tolerance.
Name red flags: painful red eye, severe confusion, fever with dry skin, inability to pass urine, severe constipation, sudden wheeze, or palpitations/syncope.
For paralytics: verbalise sedation/analgesia, airway expertise, pre-oxygenation, ventilation, capnography, TOF and recovery plan before administration.