Succinylcholine, also known as suxamethonium, is a short-acting depolarizing neuromuscular blocking agent employed chiefly to facilitate rapid endotracheal intubation and to provide skeletal muscle relaxation during surgical procedures or mechanical ventilation1, 2, 3. Here’s a detailed overview of its pharmacology:
Classification
Succinylcholine is classified as a depolarizing neuromuscular blocking agent (NMBA), listed on the World Health Organization’s List of Essential Medicines due to its importance in healthcare4.
Mechanism of Action
Succinylcholine functions by binding to the post-synaptic nicotinic acetylcholine receptors at the neuromuscular junction, causing a prolonged depolarization of the motor end-plate. This initial depolarization triggers transient muscle fasciculations, followed by muscle paralysis as the depolarization persists, inhibiting further muscle contractions5.
Pharmacokinetics
- Absorption: Not available.
- Distribution: At intravenous doses of 1 mg/kg and 2 mg/kg, the mean apparent volumes of distribution were 16.4 ± 14.7 and 5.6 ± 6.8 mL/kg, respectively5.
- Metabolism: It is rapidly metabolized by plasma cholinesterase into succinylmonocholine, which is then further hydrolyzed to succinic acid and choline5.
- Excretion: Information not available.
Indications
Succinylcholine is indicated as an adjunct to general anesthesia to facilitate tracheal intubation, and to provide skeletal muscle relaxation during surgery or mechanical ventilation2, 6.
Pharmacodynamics
The neuromuscular blockade induced by Succinylcholine occurs within 60 seconds of intravenous administration and lasts between four to six minutes. It binds to the cholinergic receptors of the motor endplate to induce membrane depolarization and eventually, muscle paralysis. The paralysis is progressive, initially affecting the muscles of the face and glottis, then the intercostals and diaphragm, followed by other skeletal muscles5.
Adverse Effects
Notably, it doesn’t affect consciousness or the pain threshold, necessitating its use in conjunction with adequate anesthesia. There have been rare occurrences of acute rhabdomyolysis with hyperkalemia, leading to ventricular dysrhythmias, cardiac arrest, and death, especially in pediatric patients with undiagnosed skeletal myopathy like Duchenne’s muscular dystrophy5.
Succinylcholine Apnea and Its Treatment
A rare but serious adverse effect is succinylcholine-induced apnea, which is commonly associated with an inherited deficiency of plasma cholinesterase. The normal treatment for succinylcholine apnea is to maintain sedation and ventilate the patient in an intensive care unit until muscle function has returned. All anaesthetists are trained to recognize succinylcholine apnea and will use a machine (a ventilator) to help the patient’s breathing until the drug wears off. Recombinant plant-derived butyrylcholinesterase was capable of counteracting and reversing apnea in two complementary models of lethal succinylcholine toxicity, completely preventing mortality.
Special Populations
The use of Succinylcholine in pediatric patients should be restricted to emergency intubation or other situations where a suitable alternative is unavailable due to the associated risks of acute rhabdomyolysis with hyperkalemia in apparently healthy pediatric patients who are later found to have undiagnosed skeletal myopathy5.
Formulations
It is available under different brand names like Anectine and suxamethonium, administered intravenously or intramuscularly6, 3.
This detailed exposition of Succinylcholine’s pharmacology encompasses its mechanism of action, pharmacokinetics, clinical uses, and other crucial aspects, facilitating an extensive understanding of its medical application and associated cautions.
