Edrophonium
Edrophonium chloride
Also known as: Enlon · Tensilon · Edrophonium chloride
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Dosing by species
Dosing data for this drug is not yet available in the VetSheet formulary. Every other section below is complete. Consult the current product label before prescribing.
Overview
Edrophonium is a short-acting, reversible acetylcholinesterase inhibitor primarily used in veterinary medicine for the diagnosis of myasthenia gravis (commonly known as the Tensilon test). It is also utilized to differentiate between myasthenic crisis (under-treatment) and cholinergic crisis (over-treatment), to treat atrial tachycardia via vagal effects, and to reverse non-depolarizing neuromuscular blockade.
Clinical Warning: Always have atropine drawn up and ready to administer when performing an edrophonium challenge due to the risk of severe bradycardia or asystole.
Mechanism of action
Edrophonium acts as a reversible and short-acting competitive inhibitor of the enzyme acetylcholinesterase at the neuromuscular junction.
Acetylcholine release → binds to receptors → normally broken down by acetylcholinesterase. Edrophonium blocks this enzyme → acetylcholine accumulates → prolonged and increased stimulation of nicotinic and muscarinic receptors, temporarily improving muscle strength in myasthenia gravis.
Safety & warnings
Contraindications
- Mechanical gastrointestinal obstruction
- Mechanical urinary tract obstruction
- Peritonitis
Adverse effects
- Nausea
- Vomiting
- Increased salivation
- Diarrhoea
- Muscle fasciculations
- Severe bradyarrhythmias
- Asystole
Precautions
Use with caution in patients with bronchial disease (especially feline asthma), bradycardia (and other arrhythmias), hypotension, renal impairment, or epilepsy.
Clinical Pearl: If edrophonium availability is limited, neostigmine may be used as an alternative diagnostic test for myasthenia gravis.
Drug interactions
Potentiates neuromuscular blockade
Monitoring
- Heart rate and rhythm (ECG recommended during administration)
- Respiratory rate and effort
- Muscle strength and tone
- Cholinergic signs (salivation, vomiting, defecation)
Pharmacokinetics
Absorption
Rapid onset of action following intravenous administration.
Overdose
Overdosage may lead to muscle fasciculations and paralysis. Severe bradyarrhythmias, even asystole, may occur if edrophonium is used to antagonize neuromuscular block without the co-injection of atropine.
Treatment: Respiration should be supported and atropine administered IV to counteract muscarinic effects.
Available products
Formulations
- Injectable: 10 mg/ml solution
Veterinary
- Edrophonium Injection BP (UK import)
- Enlon (US)
Regulatory status
Available as Enlon.
Availability may be limited; often requires special import.
Currently only available through import license in the UK.
No regulatory data for: 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Normal precautions should be observed.
Client information
Edrophonium is a diagnostic medication used exclusively in the veterinary clinic, primarily to test for a muscle weakness condition called myasthenia gravis.
- Rapid Action: The drug works within seconds to temporarily restore muscle strength in affected pets, but its effects wear off very quickly.
- Monitoring: Your veterinarian will closely monitor your pet's heart rate and breathing during the test.
- Side Effects: You may notice brief side effects like drooling, nausea, or muscle twitching. The veterinary team will have an antidote (atropine) drawn up and ready to use immediately if any serious heart rate drops occur.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.