Neuromuscular blocking agents /’2′ main types of neuromuscular blocking agents

Neuromuscular blocking agents

Pharmaceuticals known as neuromuscular blocking agents (NMBAs) obstruct nerve impulse transmission at the neuromuscular junction. NMBAs cause transient muscular paralysis by focusing on this vital nerve-skeletal muscle communication site. NMBAs fall into two primary categories: non-depolarizing compounds that competitively inhibit acetylcholine receptors and depolarizing drugs that function similarly to acetylcholine. These medications are essential in medical settings because they ensure muscular relaxation during operations including mechanical breathing, endotracheal intubation, and surgical interventions. It is imperative to exercise caution while administering these medications due to the potential for serious side effects. Vigilant monitoring and suitable reversal procedures are necessary to restore neuromuscular function following the treatment.

Neuromuscular blocking agents

There are two main types of neuromuscular blocking agents:

1.Depolarizing agents:

Depolarizing neuromuscular blocking agents (NMBAs) are a specific type of muscle relaxant that act by initially causing depolarization at the neuromuscular junction. The prototypical depolarizing agent is succinylcholine (also known as suxamethonium).

Here’s how depolarizing agents work:

  1. Mimicking Acetylcholine: Succinylcholine mimics the action of acetylcholine, the natural neurotransmitter that normally stimulates muscle contraction at the neuromuscular junction.

  2. Activation of Acetylcholine Receptors: When succinylcholine binds to the acetylcholine receptors on the muscle cell membrane, it triggers a depolarization of the muscle cell. This depolarization causes a brief contraction of the muscle.

  3. Prolonged Blockade: However, unlike acetylcholine, succinylcholine is resistant to the action of acetylcholinesterase, the enzyme that breaks down acetylcholine. As a result, succinylcholine remains bound to the receptors, preventing further stimulation. This leads to a sustained state of depolarization, causing prolonged muscle paralysis.

  4. Desensitization and Repolarization: The prolonged depolarization eventually leads to desensitization of the acetylcholine receptors, making them temporarily unresponsive to further stimulation. After desensitization, the muscle cell repolarizes, and the neuromuscular junction returns to a state where it is once again responsive to acetylcholine.

Succinylcholine is commonly used for rapid sequence intubation in emergency situations or for short surgical procedures. However, it is associated with side effects and complications, including hyperkalemia (an increase in blood potassium levels), increased intracranial pressure, and prolonged paralysis in some individuals. Therefore, its use is carefully considered, and alternatives are chosen in specific situations or for patients with contraindications.

Healthcare professionals carefully monitor patients receiving depolarizing agents, and the administration of these drugs is typically followed by mechanical ventilation until the effects wear off and normal respiratory function is restored. Additionally, the use of depolarizing agents is contraindicated in individuals with certain medical conditions or a history of adverse reactions. The reversal agent neostigmine is often used to hasten the recovery of neuromuscular function after succinylcholine administration.

2.Non-depolarizing agents:

Non-depolarizing neuromuscular blocking agents (NMBAs) are drugs that block the action of acetylcholine at the neuromuscular junction, resulting in muscle relaxation. Unlike depolarizing agents, non-depolarizing agents do not cause a persistent depolarization of the muscle membrane. Instead, they competitively bind to the nicotinic acetylcholine receptors on the motor end plate, preventing acetylcholine from binding and initiating muscle contraction.

Here are some common non-depolarizing neuromuscular blocking agents:

  1. Vecuronium: This drug has an intermediate duration of action, making it suitable for a variety of surgical procedures. Vecuronium is often used in combination with other anesthetics.

  2. Rocuronium: Similar to vecuronium, rocuronium is an intermediate-acting NMBA. It has a rapid onset and is widely used for endotracheal intubation and maintenance of muscle relaxation during surgery.

  3. Pancuronium: This drug has a longer duration of action compared to vecuronium and rocuronium, making it suitable for prolonged surgical procedures. However, its use has decreased in recent years due to concerns about side effects.

  4. Atracurium: Atracurium is an intermediate-acting NMBA that is metabolized by non-specific ester hydrolysis and Hofmann elimination. It is often chosen in situations where renal or hepatic function may be compromised.

  5. Cisatracurium: This is a closely related analog of atracurium, but with a more favorable side effect profile. Cisatracurium is also metabolized by Hofmann elimination and does not rely on hepatic or renal function for clearance.

These drugs are used in surgical and critical care settings to induce muscle relaxation during various procedures, such as endotracheal intubation, mechanical ventilation, and surgical operations. The choice of a specific non-depolarizing agent depends on factors such as the duration of action required, the patient’s medical condition, and any potential contraindications or side effects.

It’s important to note that the effects of non-depolarizing agents can be reversed with the administration of acetylcholinesterase inhibitors, such as neostigmine, along with an antimuscarinic agent (e.g., atropine or glycopyrrolate) to prevent the side effects associated with increased acetylcholine levels. Reversal agents are typically used to accelerate the recovery of neuromuscular function after surgery.


In conclusion, neuromuscular blocking agents (NMBAs) are a class of drugs used in medical settings to induce temporary muscle paralysis. There are two main types of NMBAs: depolarizing agents and non-depolarizing agents.

Depolarizing agents, exemplified by succinylcholine, initially cause muscle depolarization but then persistently block acetylcholine receptors, leading to muscle relaxation. On the other hand, non-depolarizing agents, such as vecuronium, rocuronium, pancuronium, atracurium, and cisatracurium, competitively block acetylcholine receptors, preventing muscle contraction.

NMBAs are employed in various clinical situations, including facilitating endotracheal intubation, assisting mechanical ventilation, and optimizing surgical conditions. Careful administration and monitoring are crucial to prevent complications, and these agents are typically used in conjunction with anesthetics and analgesics during medical procedures.

After the use of NMBAs, patients are often supported with mechanical ventilation until the effects wear off. The reversal agent neostigmine, often administered with atropine or glycopyrrolate, is commonly used to expedite the recovery of neuromuscular function.

The choice of a specific neuromuscular blocking agent depends on factors such as the desired duration of action, patient characteristics, and the nature of the medical procedure. Healthcare professionals must administer these drugs with expertise and closely monitor patients to ensure their safety and well-being.

Scroll to Top