Edrophonium
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: 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.
Routes of administration
Contraindications
- Mechanical gastrointestinal obstruction
- Mechanical urinary tract obstruction
- Peritonitis
Adverse effects
- Nausea
- Vomiting
- Increased salivation
- Diarrhoea
- Muscle fasciculations
- Severe bradyarrhythmias
- Asystole
Drug interactions
- Depolarizing neuromuscular relaxants (e.g., suxamethonium) · Potentiates neuromuscular blockade · major
Monitoring
- Heart rate and rhythm (ECG recommended during administration)
- Respiratory rate and effort
- Muscle strength and tone
- Cholinergic signs (salivation, vomiting, defecation)
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.
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.