Neostigmine (Neostigmin)
Cholinesterase inhibitor – reversible acetylcholinesterase inhibitor used to reverse neuromuscular blockade and treat myasthenia gravis
Neostigmine is a reversible cholinesterase inhibitor used primarily in hospital settings to reverse the effects of nondepolarizing neuromuscular blocking agents after surgery, and to treat the symptoms of myasthenia gravis. It is included on the WHO Model List of Essential Medicines and is administered by injection (intravenous, intramuscular, or subcutaneous) under direct medical supervision.
Quick Facts
Key Takeaways
- Neostigmine is a reversible acetylcholinesterase inhibitor that increases acetylcholine levels at the neuromuscular junction, improving muscle contraction
- It is most commonly used in anesthesia practice to reverse nondepolarizing neuromuscular blockade (e.g., rocuronium, vecuronium) at the end of surgery
- Always co-administered with an antimuscarinic agent (atropine or glycopyrrolate) to counteract excessive cholinergic side effects, especially bradycardia
- Used therapeutically in myasthenia gravis to improve muscle strength, and diagnostically to confirm the condition (Tensilon-like test)
- Included on the WHO Model List of Essential Medicines and available globally as a critical perioperative and neurological medication
What Is Neostigmine and What Is It Used For?
Neostigmine belongs to the pharmacological class of reversible cholinesterase inhibitors, also known as anticholinesterase agents or parasympathomimetics. It works by blocking the enzyme acetylcholinesterase (AChE) at the neuromuscular junction and at parasympathetic nerve endings throughout the body. By preventing the enzymatic breakdown of acetylcholine, neostigmine effectively increases the concentration of this critical neurotransmitter, enhancing signal transmission between nerve endings and muscle fibers.
The drug was first synthesized in 1931 by Aeschlimann and Reinert and has been used clinically since the 1930s, making it one of the longest-established medications in modern anesthesia and neurology. It remains widely used globally and is recognized by the World Health Organization as an essential medicine. Neostigmine methylsulfate is the form used in injectable preparations, available as a sterile solution at a concentration of 2.5 mg/ml.
The primary clinical indications for neostigmine injection include:
- Reversal of nondepolarizing neuromuscular blockade: After general anesthesia, muscle-relaxing drugs such as rocuronium, vecuronium, atracurium, or pancuronium are routinely administered to facilitate endotracheal intubation and surgical relaxation. Neostigmine is used at the end of surgery to reverse residual neuromuscular blockade, restoring normal muscle function and allowing the patient to breathe independently.
- Myasthenia gravis (MG): Neostigmine can be used as a diagnostic aid and for symptomatic treatment of this autoimmune neuromuscular disorder. In MG, antibodies attack acetylcholine receptors at the neuromuscular junction, leading to fluctuating muscle weakness. Neostigmine improves neurotransmission by increasing the available acetylcholine.
- Postoperative urinary retention: By stimulating the parasympathetic nervous system and increasing smooth muscle tone of the bladder (detrusor muscle), neostigmine can help restore bladder function when postoperative urinary retention occurs.
- Paralytic ileus: Neostigmine promotes intestinal motility by increasing acetylcholine activity in the gastrointestinal tract, making it useful in managing acute colonic pseudo-obstruction (Ogilvie syndrome) and postoperative ileus.
Neostigmine has a relatively rapid onset of action. When given intravenously, the onset is approximately 1–3 minutes, with peak effect at 7–10 minutes. Intramuscular injection produces effects within 20–30 minutes. The duration of action typically ranges from 40 minutes to 2.5 hours depending on the dose and route of administration. Unlike physostigmine, neostigmine is a quaternary ammonium compound and does not cross the blood–brain barrier in significant amounts, limiting central nervous system side effects.
What Should You Know Before Taking Neostigmine?
Although neostigmine is administered exclusively in clinical settings by healthcare professionals, understanding its contraindications, warnings, and precautions is essential for patient safety. The treating physician will evaluate each patient’s medical history before administration.
Contraindications
Neostigmine is absolutely contraindicated in the following conditions:
- Mechanical intestinal obstruction: Neostigmine stimulates gastrointestinal motility and can dangerously increase pressure in an obstructed bowel, risking perforation.
- Mechanical urinary tract obstruction: Increased bladder contraction against a physical obstruction can cause severe complications.
- Peritonitis: Enhanced bowel motility in the presence of peritoneal inflammation can worsen the clinical picture.
- Known hypersensitivity to neostigmine, bromides (for neostigmine bromide formulations), or any excipient in the formulation.
Warnings and Precautions
Healthcare professionals must exercise particular caution when administering neostigmine to patients with the following conditions:
- Asthma or chronic obstructive pulmonary disease (COPD): Neostigmine can cause bronchoconstriction by stimulating muscarinic receptors in bronchial smooth muscle. Patients with reactive airway disease are at increased risk of bronchospasm.
- Cardiac arrhythmias, especially bradycardia: Neostigmine has potent vagotonic effects that can cause significant bradycardia, atrioventricular block, or even asystole. Pre-treatment with atropine or glycopyrrolate is essential.
- Peptic ulcer disease: Increased gastric acid secretion and gastrointestinal motility may worsen peptic ulcers.
- Epilepsy: Although neostigmine does not readily cross the blood–brain barrier, caution is advised in patients with seizure disorders.
- Recent intestinal or bladder surgery: Enhanced smooth muscle contractions may compromise surgical anastomoses.
- Hyperthyroidism: Thyrotoxic patients may have increased sensitivity to cholinergic effects.
- Renal impairment: Neostigmine is partly excreted by the kidneys, and dose adjustment may be necessary in patients with significant renal dysfunction.
Atropine sulfate or glycopyrrolate must always be readily available when neostigmine is administered. These antimuscarinic agents are used to counteract excessive cholinergic stimulation, particularly life-threatening bradycardia. In most protocols, atropine (0.6–1.2 mg IV) or glycopyrrolate (0.2–0.4 mg IV) is given immediately before or concurrently with neostigmine.
Pregnancy and Breastfeeding
Neostigmine should be used during pregnancy only when clearly necessary and the potential benefit justifies the potential risk to the fetus. There is limited data on the use of neostigmine in pregnant women. The quaternary ammonium structure of neostigmine means it does not readily cross the placenta, providing some degree of fetal protection. However, large intravenous doses near term could theoretically cause uterine contractions and premature labor.
Neostigmine has been used safely in pregnant women with myasthenia gravis under careful medical supervision. Neonates born to mothers with myasthenia gravis should be monitored for signs of transient neonatal myasthenia regardless of maternal treatment.
It is not known whether neostigmine is excreted in human breast milk. Given its quaternary ammonium structure and low oral bioavailability, significant exposure via breast milk is considered unlikely. However, caution is recommended and the decision to breastfeed should involve a risk–benefit assessment with the treating physician.
How Does Neostigmine Interact with Other Drugs?
Drug interactions with neostigmine are clinically important and must be considered in the perioperative and neurological care setting. The interactions arise primarily from neostigmine’s mechanism of increasing acetylcholine levels at both nicotinic (neuromuscular) and muscarinic (parasympathetic) receptors.
Major Interactions
| Drug / Class | Interaction | Clinical Significance |
|---|---|---|
| Succinylcholine | Neostigmine inhibits plasma cholinesterase (butyrylcholinesterase), which normally metabolizes succinylcholine. This prolongs the duration of succinylcholine’s neuromuscular blockade. | Avoid concurrent use. Allow adequate washout time between agents. |
| Aminoglycoside antibiotics (gentamicin, tobramycin, amikacin) | These antibiotics have inherent neuromuscular blocking properties, reducing the effectiveness of neostigmine reversal. | Higher doses of neostigmine may be required. Monitor neuromuscular function closely. |
| Corticosteroids | Chronic corticosteroid use can antagonize the effects of cholinesterase inhibitors in myasthenia gravis patients, potentially worsening weakness. | Monitor for myasthenic crisis when initiating or changing corticosteroid therapy. |
| Beta-blockers | Additive bradycardic effect when combined with the vagotonic action of neostigmine. | Increased risk of severe bradycardia. Ensure adequate anticholinergic cover. |
| Magnesium sulfate | Magnesium has neuromuscular blocking properties and can antagonize the action of neostigmine. | Higher neostigmine doses may be needed. Common in obstetric patients on magnesium for pre-eclampsia. |
Minor Interactions
Several additional drug interactions, while less critical, merit awareness:
- Atropine and glycopyrrolate: These are intentionally co-administered to counteract the muscarinic effects of neostigmine. This is a beneficial and desired interaction, not an adverse one.
- Local anesthetics (ester-type): These are metabolized by plasma cholinesterase, and neostigmine may slightly prolong their duration of action.
- Other cholinesterase inhibitors (pyridostigmine, donepezil, rivastigmine): Additive cholinergic effects. Avoid concomitant use unless clinically indicated.
- Clindamycin and lincomycin: These antibiotics can potentiate neuromuscular blockade and may reduce the effectiveness of neostigmine reversal.
- Lithium: Can enhance neuromuscular blockade and reduce the effectiveness of cholinesterase inhibitors.
When planning reversal of neuromuscular blockade with neostigmine, always review the patient’s medication list for drugs that may potentiate or antagonize neuromuscular blockade. Quantitative neuromuscular monitoring (train-of-four ratio) is recommended to guide reversal timing and dosing, regardless of concomitant medications.
What Is the Correct Dosage of Neostigmine?
Neostigmine dosing is always individualized based on the clinical indication, patient weight, renal function, depth of neuromuscular blockade, and clinical response. It must be administered by or under the supervision of a physician experienced in the use of cholinesterase inhibitors, ideally an anesthesiologist or neurologist. Quantitative neuromuscular monitoring should guide dosing for the reversal of neuromuscular blockade.
Adults
Reversal of Neuromuscular Blockade
Dose: 0.03–0.07 mg/kg intravenously (IV), up to a maximum of 5 mg
Co-administration: Atropine 0.015–0.03 mg/kg IV or glycopyrrolate 0.007–0.014 mg/kg IV, given before or simultaneously
Timing: Administer when spontaneous recovery of neuromuscular function has begun (at least 1–2 twitches on train-of-four monitoring)
Onset: 1–3 minutes IV; peak effect at 7–10 minutes
Note: Do not administer more than 5 mg total. If adequate reversal is not achieved, consider sugammadex (for aminosteroid NMBAs) or assisted ventilation.
Myasthenia Gravis (Symptomatic Treatment)
Dose: 0.5–2.5 mg by intramuscular (IM) or subcutaneous (SC) injection
Frequency: Every 1–3 hours as needed, adjusted to clinical response
Maximum daily dose: Individualized; typical range 5–20 mg/day
Note: For long-term management, oral pyridostigmine (Mestinon) is generally preferred. Neostigmine injection is used when oral administration is not feasible.
Postoperative Urinary Retention / Paralytic Ileus
Dose: 0.5–1 mg by IM or SC injection
Frequency: May repeat every 3 hours for 2–3 doses if needed
Note: Catheterization should be considered if no response after 2 doses. For Ogilvie syndrome, IV neostigmine 2 mg over 3–5 minutes has been used under cardiac monitoring.
Children
Reversal of Neuromuscular Blockade (Pediatric)
Dose: 0.04–0.08 mg/kg IV
Co-administration: Atropine 0.02 mg/kg IV (minimum 0.1 mg)
Maximum single dose: 2.5 mg in infants and younger children; up to 5 mg in older children/adolescents
Note: Pediatric patients may require relatively higher doses on a per-kilogram basis compared to adults. Neuromuscular monitoring is essential.
Myasthenia Gravis (Pediatric)
Dose: 0.01–0.04 mg/kg IM or SC every 2–4 hours
Note: Doses are carefully titrated to effect. Oral pyridostigmine is preferred for maintenance therapy when feasible.
Elderly
Elderly patients may be more sensitive to the effects of neostigmine, particularly its cardiovascular effects (bradycardia) and may have reduced renal clearance. Starting at the lower end of the dosage range is recommended, with careful titration based on clinical response and neuromuscular monitoring. The co-administered anticholinergic agent dose should be maintained or even increased to protect against bradycardia, as elderly patients often have underlying conduction system disease.
Missed Dose
As neostigmine injection is administered by healthcare professionals in a clinical setting, missed doses are not a practical concern for patients. In the context of scheduled dosing for myasthenia gravis (IM or SC), if a dose is missed, it should be given as soon as remembered. If it is nearly time for the next dose, the missed dose should be skipped—do not double the dose.
Overdose
Overdose of neostigmine produces a cholinergic crisis, characterized by excessive muscarinic and nicotinic stimulation. Symptoms include severe bradycardia, hypotension, excessive salivation, lacrimation, urination, defecation (SLUD syndrome), bronchospasm, bronchorrhea, miosis, muscle fasciculations followed by paralysis, respiratory failure, and potentially death.
Treatment: Immediate discontinuation of neostigmine. Atropine sulfate (1–2 mg IV, repeated as needed) is the primary antidote for muscarinic symptoms. Supportive care including mechanical ventilation may be required. Atropine does not reverse nicotinic effects (muscle weakness/paralysis), which must be managed with ventilatory support until the drug is cleared.
What Are the Side Effects of Neostigmine?
The side effects of neostigmine are a direct consequence of increased acetylcholine activity at muscarinic and nicotinic receptors throughout the body. The muscarinic effects (affecting the heart, glands, smooth muscle, and gastrointestinal tract) are the most clinically troublesome and are routinely managed by co-administration of an anticholinergic agent. The frequency classification below follows the European Medicines Agency convention.
Very Common
Affects more than 1 in 10 patients (>10%)
- Bradycardia (slow heart rate)
- Nausea
- Increased salivation (sialorrhea)
- Increased bronchial secretions
- Abdominal cramps
Common
Affects 1 to 10 in 100 patients (1–10%)
- Vomiting
- Diarrhea
- Miosis (pupil constriction)
- Increased sweating (diaphoresis)
- Increased lacrimation (tearing)
- Urinary urgency or frequency
- Muscle fasciculations
Uncommon
Affects 1 to 10 in 1,000 patients (0.1–1%)
- Hypotension (low blood pressure)
- AV block (heart conduction delay)
- Bronchospasm
- Skin rash or urticaria
- Muscle weakness (paradoxical, at high doses)
Rare
Affects fewer than 1 in 1,000 patients (<0.1%)
- Cardiac arrest (typically in predisposed patients)
- Anaphylaxis / severe allergic reaction
- Seizures
- Cholinergic crisis (with overdose)
The distinction between cholinergic side effects and a cholinergic crisis is critical. Mild muscarinic symptoms (slight increase in salivation, mild bradycardia) are expected and managed with the co-administered anticholinergic agent. However, if a patient develops severe symptoms such as profuse secretions, respiratory distress, or progressive muscle weakness, immediate intervention is required, as these signs indicate overdosage or a cholinergic crisis.
In the perioperative setting, the most clinically relevant side effects are bradycardia and increased airway secretions. Both are routinely prevented by the anticholinergic agent given alongside neostigmine. The choice of anticholinergic matters: glycopyrrolate has a more predictable onset that matches neostigmine’s, resulting in more stable heart rates, while atropine may produce initial tachycardia followed by bradycardia.
If you experience any unusual or severe symptoms after receiving neostigmine, inform your healthcare provider immediately. Reporting suspected adverse reactions through your country’s pharmacovigilance system (e.g., Yellow Card Scheme in the UK, MedWatch in the US, EudraVigilance in the EU) helps ensure the ongoing safe use of this medication.
How Should You Store Neostigmine?
Neostigmine injection is a hospital-use medication and is typically stored in the pharmacy or anesthesia drug cabinet. Patients do not normally need to store this medicine at home. However, the following storage guidelines apply to healthcare facilities:
- Temperature: Store at controlled room temperature between 15°C and 25°C (59°F to 77°F). Brief excursions up to 30°C (86°F) may be permitted according to the manufacturer’s specifications.
- Light protection: Keep ampoules in the outer carton to protect from light. Prolonged exposure to light can cause degradation of the active substance.
- Freezing: Do not freeze. Freezing may cause crystallization or alterations in the formulation.
- Inspection before use: Visually inspect the solution before administration. Use only if the solution is clear and colorless to slightly yellow. Discard if it appears discolored, turbid, or contains visible particles.
- Single-use ampoules: For single-use ampoules, any unused portion should be discarded immediately after opening. Do not store opened ampoules for later use.
- Shelf life: Follow the expiry date printed on the packaging. Typical shelf life is 3–5 years when stored correctly, depending on the manufacturer.
Keep all medicines out of the reach of children. Disposal of unused or expired neostigmine should follow local regulations for pharmaceutical waste disposal, typically through a hospital pharmacy return program.
What Does Neostigmine Contain?
The composition of neostigmine injection varies slightly between manufacturers, but the core formulation is consistent:
| Component | Role | Amount |
|---|---|---|
| Neostigmine methylsulfate | Active ingredient (cholinesterase inhibitor) | 2.5 mg per ml |
| Sodium chloride | Tonicity agent (makes solution isotonic) | q.s. |
| Glacial acetic acid | pH adjustment | q.s. to pH 5.0–6.5 |
| Sodium acetate trihydrate | Buffer | q.s. |
| Water for injection | Solvent | to 1 ml |
Neostigmine methylsulfate is a white, crystalline, odorless powder that is freely soluble in water. Its molecular formula is C13H22N2O4·CH4O3S (molecular weight 334.39 g/mol). It is a quaternary ammonium compound, which means it carries a permanent positive charge and therefore does not cross the blood–brain barrier to a significant extent. This is an important pharmacological distinction from physostigmine, which is a tertiary amine that readily enters the central nervous system.
The injectable solution does not contain preservatives such as parabens, sulfites, or benzyl alcohol in most single-dose ampoule formulations. Multi-dose vials, where available, may contain methylparaben or other preservatives—check the specific product labeling. The solution is typically clear and colorless, with a pH between 5.0 and 6.5.
Frequently Asked Questions About Neostigmine
Neostigmine is primarily used to reverse nondepolarizing neuromuscular blockade after surgery (given alongside atropine or glycopyrrolate), to treat and diagnose myasthenia gravis, and to manage postoperative urinary retention or paralytic ileus. It is administered by injection in hospital settings by healthcare professionals.
Neostigmine works by reversibly inhibiting the enzyme acetylcholinesterase, which normally breaks down acetylcholine. By preventing this breakdown, neostigmine increases the concentration of acetylcholine at the neuromuscular junction and other cholinergic synapses, improving nerve-to-muscle signal transmission and muscle contraction.
The most common side effects of neostigmine include nausea, vomiting, increased salivation, abdominal cramps, diarrhea, and bradycardia (slow heart rate). These effects are due to its cholinergic activity. Atropine or glycopyrrolate is usually given alongside neostigmine to counteract these muscarinic side effects, especially bradycardia.
No. Neostigmine injection is administered only in hospital or clinical settings by healthcare professionals. It requires careful dose titration and monitoring of vital signs, including heart rate and respiratory function. For home management of myasthenia gravis, oral pyridostigmine (Mestinon) is the standard alternative.
Atropine (or glycopyrrolate) is given with neostigmine to block unwanted muscarinic side effects, particularly severe bradycardia (dangerously slow heart rate), excessive salivation, and bronchoconstriction. Neostigmine increases acetylcholine throughout the body, and atropine selectively blocks the muscarinic receptors while allowing the desired nicotinic (neuromuscular) effects.
Yes. Neostigmine is included on the WHO Model List of Essential Medicines as a cholinesterase inhibitor for the treatment of myasthenia gravis and for reversal of neuromuscular blockade. This designation confirms its importance as a safe and effective medicine that should be available globally in healthcare systems.
References
- World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd List, 2023. Neostigmine listed under Section 20: Muscle relaxants (peripherally-acting) and cholinesterase inhibitors.
- European Medicines Agency (EMA). Neostigmine methylsulfate – Summary of Product Characteristics. Available at: ema.europa.eu. Accessed January 2026.
- U.S. Food and Drug Administration (FDA). Bloxiverz (neostigmine methylsulfate injection) – Prescribing Information. Approved 2013, updated 2024.
- British National Formulary (BNF). Neostigmine. National Institute for Health and Care Excellence (NICE). Accessed January 2026.
- Brull SJ, Kopman AF. Current Status of Neuromuscular Reversal and Monitoring: Challenges and Opportunities. Anesthesiology. 2017;126(1):173-190. doi:10.1097/ALN.0000000000001409
- Naguib M, Brull SJ, Kopman AF, et al. Consensus Statement on Perioperative Use of Neuromuscular Monitoring. Anesth Analg. 2018;127(1):71-80. doi:10.1213/ANE.0000000000002670
- Gilhus NE, Tzartos S, Evoli A, et al. Myasthenia gravis. Nat Rev Dis Primers. 2019;5(1):30. doi:10.1038/s41572-019-0079-y
- Pongracz A, Szatmari S, Nemes R, et al. Reversal of Neuromuscular Blockade with Sugammadex or Neostigmine: A Systematic Review and Meta-Analysis. Anesthesiology. 2021;134(6):930-950.
- International Council for Harmonisation (ICH). Guideline for Stability Testing of New Drug Substances and Products. ICH Q1A(R2).
- Martindale: The Complete Drug Reference. Neostigmine Metilsulfate. Pharmaceutical Press, 40th edition, 2024.
About the Editorial Team
This article was written and reviewed by the iMedic Medical Editorial Team, comprising licensed specialists in neurology, anesthesiology, pharmacology, and clinical medicine. Our content follows the GRADE evidence framework and is based on peer-reviewed research, international clinical guidelines (WHO, EMA, FDA, BNF), and established medical standards.
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