Suxamethonium Chloride (Succinylcholine Chloride) is a depolarizing neuromuscular blocking agent of rapid onset and short duration of action. It is a quaternary ammonium compound that acts as an agonist at nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction, causing initial fasciculations followed by sustained depolarization and flaccid paralysis. It is a standard agent for rapid sequence intubation (RSI) in emergency and surgical settings across India due to its predictable profile, but its use is tempered by significant adverse effects like hyperkalemia, malignant hyperthermia, and bradycardia.
Adult: IV: 0.6-1.2 mg/kg (typically 1 mg/kg). For rapid sequence intubation: 1-1.5 mg/kg. Maximum single dose: 150 mg. IM (if IV not possible): Up to 2.5-4 mg/kg (not to exceed 150 mg).
Note: For IV use only, except in specific circumstances where IM route is used. Must be administered as a rapid IV bolus. Do not mix with alkaline solutions (e.g., thiopentone) as precipitation occurs. Always ensure patient is adequately sedated and under supervision with facilities for intubation and ventilation. Pre-treatment with a small dose of a non-depolarizing agent (e.g., atracurium 0.01 mg/kg) can reduce fasciculations and postoperative myalgia.
Suxamethonium is a dicholine ester that mimics the action of acetylcholine (ACh) at the postjunctional membrane of the neuromuscular junction. It binds to nicotinic ACh receptors, causing depolarization of the motor endplate, which is seen clinically as muscle fasciculations. Unlike ACh, it is not hydrolyzed efficiently at the synaptic cleft by acetylcholinesterase. It persists at the receptor, causing a persistent depolarization that renders the endplate refractory to further stimulation by ACh, leading to flaccid paralysis (Phase I block). With prolonged exposure, it can lead to a Phase II block (desensitization block).
Pregnancy: Category C: Crosses the placenta. May cause fetal bradycardia and prolonged weakness in neonate if mother has pseudocholinesterase deficiency. Use only if clearly needed, preferably in first trimester. Avoid in second/third trimester for elective procedures due to risk of prolonged neonatal apnea.
Driving: Patients must be warned that muscle weakness and fatigue may persist for several hours after administration. They should not drive or operate machinery until full muscle strength returns, which is typically after full recovery from anesthesia.
| Aminoglycosides (Gentamicin, Amikacin) | Potentiate neuromuscular blockade, may cause prolonged apnea. | Major |
| Beta-blockers (Propranolol) | Enhanced bradycardic effect of suxamethonium. | Moderate |
| Magnesium Sulfate | Potentiates neuromuscular blockade. | Major |
| Lithium | Prolongs duration of neuromuscular blockade. | Moderate |
| Cyclophosphamide | Reduces plasma pseudocholinesterase activity, prolonging effect. | Major |
| Echothiophate eye drops | Irreversibly inhibits pseudocholinesterase, causing prolonged apnea. | Major |
| Procaine | Competes for pseudocholinesterase, prolonging effect. | Moderate |
| Non-depolarizing NMBAs (e.g., Atracurium, Rocuronium) | Prior use can antagonize or potentiate effects of suxamethonium depending on timing. | Moderate |