Neostigmine

7 min read Last updated April 9, 2026

How to use in theatre (practical approach)

  • Confirm appropriate depth of block before giving reversal
    • Aim for TOF count 4 with fade (or better), ideally TOF ratio improving and/or clinical signs returning
    • Neostigmine has a ceiling effect—ineffective for profound block (e.g. PTC only)
  • Dose neostigmine and antimuscarinic together
    • Typical adult dose: 0.04–0.07 mg/kg IV (max commonly 5 mg), titrate to monitoring and clinical context
    • Give with glycopyrrolate 0.01 mg/kg IV (or atropine 0.02 mg/kg IV) to mitigate muscarinic effects
  • Timing and expectations
    • Onset within minutes, peak effect ~7–10 min, duration ~30–60+ min (variable)
    • Extubation target: TOF ratio ≥0.9 plus satisfactory clinical recovery
  • If inadequate reversal
    • Check: residual anaesthetic/opioid, hypothermia, electrolyte disturbance (Mg2+), acidosis, NMBD dosing/agent, monitoring site, equipment
    • Avoid repeated large neostigmine doses once near full recovery (risk paradoxical weakness/cholinergic effects), support ventilation and reassess

When to avoid / be cautious

  • Bradyarrhythmias and conduction disease
    • Always co-administer antimuscarinic, be prepared to treat severe bradycardia/asystole (rare but reported)
  • Asthma/COPD and bronchospasm risk
    • Muscarinic bronchoconstriction and secretions, glycopyrrolate preferred over atropine for less tachycardia/central effects
  • Bowel/urinary obstruction
    • Cholinergic stimulation may worsen obstruction, consider alternatives/supportive strategy depending on urgency
  • Myasthenia gravis and other neuromuscular disorders
    • Response to NMBDs and reversal is unpredictable, use quantitative monitoring and careful titration, consider sugammadex if aminosteroid NMBD used

Classification and key role

  • Reversible acetylcholinesterase inhibitor (carbamate) used to reverse non-depolarising neuromuscular blockade
  • Quaternary ammonium compound → poorly lipid soluble → minimal CNS penetration

Mechanism of action (NMJ and autonomic)

  • Inhibits acetylcholinesterase by carbamylation → increases ACh concentration at nicotinic receptors at NMJ → competitively displaces non-depolarising NMBD
  • Also increases ACh at muscarinic receptors → bradycardia, bronchoconstriction, secretions, GI motility, miosis
  • Ceiling effect: once AChE maximally inhibited, further dose does not increase reversal, excess ACh may impair neuromuscular transmission (depolarising-like weakness)

Pharmacokinetics

  • Route: IV for reversal (also IM/SC/oral in other indications)
  • Onset: ~1–3 min, peak: ~7–10 min, duration: ~30–60+ min (context dependent)
  • Distribution: low lipid solubility, limited CNS entry, crosses placenta to some extent (clinical relevance usually limited)
  • Elimination: renal excretion significant, some hepatic metabolism, prolonged effect in renal impairment

Dose and co-administration

  • Neostigmine 0.04–0.07 mg/kg IV (often 2.5–5 mg adult) depending on depth of block and agent used
  • Glycopyrrolate 0.01 mg/kg IV (typical adult 0.4–0.8 mg) given with neostigmine, commonly mixed in same syringe
  • Atropine 0.02 mg/kg IV is an alternative antimuscarinic (more tachycardia, crosses BBB)
  • Avoid giving antimuscarinic long before neostigmine (risk unopposed muscarinic effects when neostigmine peaks) and avoid neostigmine without antimuscarinic

Effects (system by system)

  • Cardiovascular: bradycardia, AV block, hypotension, rarely severe bradycardia/asystole (especially with high vagal tone, opioids, beta-blockers, conduction disease)
  • Respiratory: bronchoconstriction, increased secretions, may worsen reactive airway disease
  • GI/GU: increased peristalsis, cramps, diarrhoea, increased salivation, urinary urgency
  • Eye: miosis, lacrimation
  • NMJ: improves transmission in presence of non-depolarising block, excessive ACh can cause weakness/fasciculations (cholinergic excess)

Interactions and special situations

  • Profound block: neostigmine unreliable, consider waiting for spontaneous recovery or use sugammadex if rocuronium/vecuronium used
  • Volatile agents potentiate NMBDs → may delay recovery, ensure adequate time and monitoring before reversal
  • Aminoglycosides, magnesium, lithium can potentiate block and impair reversal
  • Suxamethonium: anticholinesterases can prolong phase I block by inhibiting plasma cholinesterase, may antagonise phase II block—clinically avoid routine use for sux reversal
  • Renal impairment: prolonged neostigmine effect and muscarinic side effects, dose carefully and use quantitative monitoring

Adverse effects and management

  • Cholinergic effects: bradycardia, bronchospasm, secretions, nausea/vomiting, abdominal cramps
  • Treat severe muscarinic effects with antimuscarinic (glycopyrrolate/atropine) and supportive care (oxygen, bronchodilators, fluids/vasopressors as needed)
  • Cholinergic crisis (rare perioperatively): weakness + muscarinic signs, manage with airway/ventilation, atropine for muscarinic symptoms, and stop further anticholinesterase

Comparison: neostigmine vs sugammadex (high-yield)

  • Neostigmine: indirect reversal, requires some recovery, ceiling effect, muscarinic side effects, inexpensive
  • Sugammadex: encapsulates rocuronium/vecuronium, can reverse deep block rapidly, fewer cholinergic effects, cost and anaphylaxis considerations

Test yourself…

Describe the mechanism by which neostigmine reverses non-depolarising neuromuscular blockade.

Key points expected: site of action, enzyme interaction, effect on ACh, and why it only works when some recovery has occurred.

  • Neostigmine is a reversible acetylcholinesterase inhibitor (carbamate) → carbamylates AChE and inhibits breakdown of acetylcholine
  • Increased ACh at the NMJ increases competition at nicotinic receptors → displaces non-depolarising NMBD from receptors
  • Requires partial spontaneous recovery: if too many receptors are occupied (deep block), increased ACh cannot restore transmission effectively
  • Also increases ACh at muscarinic receptors → necessitates co-administration of an antimuscarinic
Why must neostigmine be given with an antimuscarinic? Compare glycopyrrolate and atropine.

Examiners look for muscarinic side effects, timing, and drug properties (quaternary vs tertiary).

  • Neostigmine increases ACh at muscarinic receptors → bradycardia/AV block, bronchospasm, secretions, increased GI motility, miosis
  • Glycopyrrolate: quaternary ammonium → minimal CNS penetration, less tachycardia, good antisialagogue, commonly paired with neostigmine
  • Atropine: tertiary amine → crosses BBB, more tachycardia, may be preferred in profound bradycardia but can cause central effects (especially in children/elderly)
  • Give together to match onset and avoid periods of unopposed muscarinic activity
What is meant by the &#039,ceiling effect&#039, of neostigmine and what are the clinical implications?

This is commonly examined around residual paralysis and inappropriate redosing.

  • AChE becomes maximally inhibited at clinically used doses, further neostigmine does not meaningfully increase ACh at NMJ
  • Therefore neostigmine cannot reliably reverse deep block (e.g. PTC only), must wait for recovery or use sugammadex (if appropriate NMBD)
  • Excess ACh can worsen neuromuscular transmission (depolarising-like effect) and increase muscarinic adverse effects
Give a typical dosing regimen for neostigmine and glycopyrrolate for reversal in an adult and explain how you would titrate it.

Expect dose ranges, maximum dose, and titration to quantitative monitoring.

  • Neostigmine 0.04–0.07 mg/kg IV (often 2.5–5 mg total adult), glycopyrrolate 0.01 mg/kg IV (often 0.4–0.8 mg)
  • Titrate to depth of block: smaller dose if TOF ratio already near 0.9, larger dose if TOF count 4 with clear fade
  • Avoid routine full-dose neostigmine when already recovered (risk cholinergic effects and paradoxical weakness)
A patient has TOF count 1 at the adductor pollicis at the end of surgery. Is neostigmine appropriate? What would you do?

This tests understanding of depth of block and limitations of neostigmine.

  • TOF count 1 indicates relatively deep block, neostigmine may be slow/unreliable and may not achieve timely TOF ≥0.9
  • Options: wait for further spontaneous recovery (optimize temperature, acid-base, electrolytes) then give neostigmine when TOF count improves
  • If rocuronium/vecuronium used and rapid reversal needed, consider sugammadex according to depth of block and local guidance
  • Continue ventilation/anaesthesia until objective recovery achieved
Explain why giving neostigmine after full recovery from neuromuscular block can cause weakness.

Often asked as a concept question about &#039,paradoxical weakness&#039,.

  • With minimal NMBD present, excess ACh from AChE inhibition can desensitise nicotinic receptors and produce a depolarising-like block
  • Additionally, muscarinic effects (bronchospasm/secretions) can mimic poor recovery clinically
  • Hence use quantitative monitoring and avoid unnecessary neostigmine when TOF ratio already ≥0.9
List the main adverse effects of neostigmine and how you would manage severe bradycardia after administration.

Expect system-based list and immediate management steps.

  • Adverse effects: bradycardia/AV block, hypotension, bronchospasm, increased secretions, nausea/vomiting, abdominal cramps/diarrhoea, miosis
  • Management of severe bradycardia: oxygen, check pulse/ECG, stop surgical vagal stimulus, give atropine IV (or additional glycopyrrolate), consider adrenaline if refractory, support circulation
  • Consider contributing factors: high vagal tone, opioids, beta-blockade, hypoxia, conduction disease
How does neostigmine interact with suxamethonium? Would you use it to reverse suxamethonium?

This is a classic FRCA pharmacology viva topic.

  • Anticholinesterases inhibit plasma cholinesterase → can prolong suxamethonium metabolism and therefore prolong phase I block
  • In phase II block, anticholinesterases may antagonise block, but this is unpredictable and not routine practice
  • Therefore neostigmine is not used to reverse typical suxamethonium block, manage with ventilation/sedation until recovery
Outline factors that may cause failure of reversal after neostigmine despite apparently adequate dosing.

This tests differential diagnosis of residual paralysis and perioperative physiology.

  • Given too early (deep block) → ceiling effect and inadequate reversal
  • Potentiation of NMBD: volatile anaesthetics, aminoglycosides, magnesium, lithium
  • Physiology: hypothermia, acidosis, electrolyte disturbance (hypocalcaemia, hypermagnesaemia), poor perfusion
  • Monitoring issues: wrong site, poor calibration, movement artefact, clinical signs unreliable without quantitative monitoring
  • Non-NMBA causes of weakness: residual anaesthetic/opioid, hypoglycaemia, stroke, myopathy, myasthenic syndromes
Explain why quantitative neuromuscular monitoring is recommended when using neostigmine.

Often linked to awareness of residual paralysis and TOF ratio targets.

  • Clinical tests and qualitative fade detection are insensitive for residual block, significant weakness can persist with TOF ratio 0.4–0.9
  • Extubation should target TOF ratio ≥0.9 to reduce airway obstruction, hypoxia, aspiration risk and postoperative pulmonary complications
  • Quantitative monitoring guides appropriate timing/dose and avoids unnecessary neostigmine when already recovered

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