Edrophonium Chloride
Edrophonium chloride is a **short-acting, parenteral anticholinesterase agent** primarily utilized in veterinary medicine for the presumptive diagnosis of **myasthenia gravis (MG)** via the 'Tensilon Test'. While it can also be used to reverse non-depolarizing neuromuscular blocking agents or treat specific supraventricular tachycardias (SVTs), its extremely short duration of action often makes longer-acting alternatives (like neostigmine or pyridostigmine) more practical for these secondary indications. > **Clinical Pearl:** The 'Tensilon Test' has a fair percentage of false-positives and false-negatives. It is best used as a rapid, presumptive diagnostic tool while awaiting results from more specific and sensitive assays, such as the acetylcholine receptor (AChR) antibody test.
Mechanism: Edrophonium acts as a rapid, reversible inhibitor of the enzyme **acetylcholinesterase**. **Mechanism of Action:** Edrophonium briefly attaches to **acetylcholinesterase** → inhibits its hydrolytic activity → **acetylcholine** accumulates in the synaptic cleft → prolonged and increased stimulation of nicotinic and muscarinic receptors. In patients with myasthenia gravis, the sudden surge of acetylcholine temporarily overcomes the autoimmune blockade/destruction of nicotinic receptors at the neuromuscular junction, leading to a rapid (but transient) return of muscle strength. Systemically, acetylcholine accumulation also causes parasympathomimetic effects including miosis, increased intestinal muscle tone, bronchoconstriction, salivation, and bradycardia.
Dosing by species
- Presumptive diagnosis of myasthenia gravis (MG) · 0.25 to 0.5 mg (total dose) · IV · Once · Patient is gently exercised until fatigued. Place indwelling catheter. Have atropine drawn up (0.02-0.04 mg/kg IV) in case cholinergic signs develop. Flush catheter with sterile saline, then immediately lightly exercise or encourage to rise.
- Presumptive diagnosis of myasthenia gravis (MG) · 0.1 mg/kg · IV · Once · Pre-treat with atropine (0.02-0.04 mg/kg IM or SC). In affected animals, paresis should resolve within one minute and effects should last for up to 15 minutes.
- Presumptive diagnosis of myasthenia gravis (MG) · 0.1-0.2 mg/kg · IV · Once · Patient is gently exercised until fatigued. Place indwelling catheter. Have atropine drawn up (0.02-0.04 mg/kg IV) in case cholinergic signs develop. Flush catheter with sterile saline, then immediately lightly exercise or encourage to rise.
- Presumptive diagnosis of myasthenia gravis (MG) · 1-10 mg (total dose) · IV · Once · Presumptive positive test results in transient improvement in clinical weakness.
- Presumptive diagnosis of myasthenia gravis (MG) · 0.1-0.2 mg/kg · IV · Once · Have atropine and endotracheal tube readily available in case of overdose.
- Presumptive diagnosis of myasthenia gravis (MG) · 0.1 mg/kg · IV · Once · Pre-treat with atropine (0.02-0.04 mg/kg IM or SC). In affected animals, paresis should resolve within one minute and effects should last for up to 15 minutes.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Bronchial asthma
- Mechanical urinary tract obstruction
- Mechanical intestinal tract obstruction
- Known hypersensitivity to the drug
Adverse effects
- Urination
- Lacrimation
- Vomiting
- Defecation
- Bradycardia
- Bronchospasm
- Salivation
Drug interactions
- Atropine · Antagonizes the muscarinic effects of edrophonium. Concurrent use should be done cautiously as atropine can mask the early clinical signs of a cholinergic crisis.
- Dexpanthenol · Theoretically may have additive cholinergic effects when used with edrophonium.
- Digoxin · Edrophonium's cardiac effects may be increased; excessive slowing of heart rate (bradycardia) may occur.
- Depolarizing Muscle Relaxants (e.g., succinylcholine, decamethonium) · Edrophonium may prolong the Phase I block of these agents.
- Non-depolarizing Muscle Relaxants (e.g., pancuronium, tubocurarine, vecuronium, atracurium) · Edrophonium antagonizes the neuromuscular blocking actions of these agents.
Monitoring
- Cholinergic adverse effects (heart rate, respiratory rate/effort, salivation)
- Improvement of paresis (for 1-15 minutes) for presumptive diagnosis of myasthenia gravis
Overdose
Overdosage of edrophonium may induce a **cholinergic crisis**. **Clinical Signs of Toxicity (SLUDGE syndrome and beyond):** - **GI:** Nausea, vomiting, diarrhea, salivation - **Respiratory:** Increased bronchial secretions, bronchospasm, pulmonary edema, respiratory paralysis - **Ophthalmic:** Miosis, blurred vision, lacrimation - **Cardiovascular:** Bradycardia or tachycardia, cardiospasm, hypotension, cardiac arrest - **Musculoskeletal:** Muscle cramps, profound weakness, sweating (in animals with sweat glands) > **Treatment:** Consists of immediate respiratory and cardiac supportive therapy. Administer **atropine** IV to counteract severe 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.