Succinylcholine Chloride
Succinylcholine chloride is an ultrashort-acting, depolarizing skeletal muscle relaxant (paralytic). **Key Clinical Points:** * **No Analgesia or Sedation:** Succinylcholine provides absolutely no pain relief or unconsciousness. Patients are fully awake and can feel pain but are completely paralyzed. It must *always* be used with appropriate sedatives, anesthetics, and analgesics. * **Ventilatory Support Required:** Because it paralyzes the diaphragm and intercostal muscles, mechanical ventilation is mandatory until the drug wears off. * **Clinical Use:** Primarily used for short-term muscle relaxation to facilitate endotracheal intubation (Rapid Sequence Intubation), surgical/diagnostic procedures, or to reduce muscle contractions during convulsions. * **Species Differences:** While it has a very short duration in humans and most animals (2-3 minutes), dogs exhibit an idiosyncratic prolonged duration of action (≈ 20 minutes). * **Modern Usage:** Its use in veterinary medicine has largely been supplanted by non-depolarizing agents (e.g., atracurium, rocuronium) which have fewer adverse effects and are reversible.
Mechanism: Succinylcholine acts as a depolarizing neuromuscular blocker. * **Binding:** It acts as a structural analog of acetylcholine (ACh) and binds to **nicotinic acetylcholine receptors (nAChRs)** at the motor endplate of the neuromuscular junction. * **Depolarization:** Unlike ACh, which is instantly degraded by acetylcholinesterase, succinylcholine remains bound, causing prolonged depolarization of the muscle membrane. This initial depolarization manifests clinically as transient muscle twitches (**fasciculations**). * **Paralysis:** Because the membrane cannot repolarize, it becomes unresponsive to subsequent ACh release → **flaccid paralysis** (Phase I block). * **Metabolism:** The blockade persists until succinylcholine diffuses away from the receptor and is rapidly hydrolyzed by **plasma pseudocholinesterase** (butyrylcholinesterase) in the blood.
Dosing by species
- Muscle relaxation · 0.06 mg/kg · IV · Single dose
- Muscle relaxation · 0.11 mg/kg · IV · Single dose
- Muscle relaxation · 0.088-0.11 mg/kg · IV, IM · Single dose · See Precautions. ARCI UCGFS Class 2 Drug. 0.088 mg/kg IV may paralyze skeletal muscles without causing respiratory depression, but higher doses cause apnea.
- Muscle relaxation · 0.07 mg/kg · IV · Single dose
- Muscle relaxation · 0.22 mg/kg · IV · Single dose
- To relax an animal to allow intubation · 0.5-1 mg/kg · IM · Single dose · Especially helpful with turtles and crocodilians.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Severe liver disease
- Chronic anemias
- Chronic malnourishment
- Glaucoma or penetrating eye injuries
- Predisposition to malignant hyperthermia
- Increased CPK values with resultant myopathies
- Recent use of organophosphate agents
Adverse effects
- Muscle soreness
- Histamine release
- Malignant hyperthermia
- Excessive salivation
- Hyperkalemia
- Rash
- Myoglobinemia
- Myoglobinuria
- Bradycardia
- Tachycardia
- Hypertension
- Hypotension
- Arrhythmias
Drug interactions
- Amphotericin B · May increase succinylcholine's effects by causing electrolyte imbalances
- Digoxin · Succinylcholine may cause a sudden outflux of potassium from muscle cells, causing arrhythmias in digitalized patients
- Opiates · Potential for increased incidences of bradycardia and sinus arrest
- Thiazide Diuretics · May increase succinylcholine's effects by causing electrolyte imbalances
- Aminoglycosides · May increase or prolong neuromuscular blockade
- Inhalant Anesthetics (Isoflurane, Desflurane) · May increase or prolong neuromuscular blockade
- Antiarrhythmics (Quinidine, Lidocaine, Procainamide) · May increase or prolong neuromuscular blockade
- Beta-Adrenergic Blockers · May increase or prolong neuromuscular blockade
- Corticosteroids · May increase or prolong neuromuscular blockade
- Magnesium Salts · May increase or prolong neuromuscular blockade
- Organophosphates · May increase or prolong neuromuscular blockade (Contraindicated)
Monitoring
- Level of muscle relaxation
- Cardiac rate and rhythm (ECG)
- Respiratory depressant effect (Apnea)
- Oxygenation (Pulse oximetry) and Ventilation (Capnography)
- Body temperature (risk of malignant hyperthermia)
Overdose
Inadvertent overdoses, or standard doses in patients deficient in pseudocholinesterase, may result in **prolonged apnea**. * **Treatment:** Mechanical ventilation with 100% O2 must be maintained until full spontaneous recovery occurs. * **Phase II Block:** Repeated or prolonged high dosages may cause patients to convert from a depolarizing (Phase I) block to a non-depolarizing-like (Phase II) block.
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.