Difference Between Depolarizing and Nondepolarizing Neuromuscular Blockers

The key difference between depolarizing and nondepolarizing neuromuscular blockers is that depolarizing neuromuscular blockers act as acetylcholine receptor agonists while nondepolarizing neuromuscular blockers act as competitive antagonists.

Neuromuscular blockers are commonly used for skeletal muscle relaxation. They are also called skeletal muscle relaxants. They block neuromuscular transmission at the neuromuscular junction (junction between neuron and muscle). As a result, muscle does not contract and remains relaxed. Neuromuscular blocking drugs are useful in surgeries. There are two types of neuromuscular blocking agents that work at a neuromuscular junction. They are depolarizing and nondepolarizing neuromuscular blockers. Depolarizing neuromuscular blockers function as acetylcholine receptor agonists. In contrast, nondepolarizing neuromuscular blockers function as competitive antagonists. Neuromuscular blocking agents are generally structural analogs of acetylcholine.

CONTENTS

1. Overview and Key Difference
2. What are Depolarizing Neuromuscular Blockers
3. What are Nondepolarizing Neuromuscular Blockers
4. Similarities Between Depolarizing and Nondepolarizing Neuromuscular Blockers
5. Side by Side Comparison – Depolarizing vs Nondepolarizing Neuromuscular Blockers in Tabular Form
6. Summary

What are Depolarizing Neuromuscular Blockers?

Depolarizing neuromuscular blockers are one of the two types of neuromuscular blocking drugs. They are noncompetitive for the binding sites of acetylcholine to receptors. Therefore, they work as acetylcholine receptor agonists by binding to Ach receptors. They do not degrade once they bind to receptors, unlike acetylcholine degraded by acetylcholinesterase.

They are resistant, so they do not metabolize and remains bound. As a result, depolarization of the muscle remains for a longer time without letting the endplate to repolarize. It leads to muscle fasciculations and paralysis of the patient. Finally, the muscle becomes relaxed. Succinylcholine is the most well-known depolarizing neuromuscular blocking agent. It is a structural analog of acetylcholine.

What are Nondepolarizing Neuromuscular Blockers?

Nondepolarizing muscular blockers are competitive antagonists. They compete with acetylcholine for binding with receptors and prevent binding of acetylcholine with the receptors. Though they are structural analogs of acetylcholine, once they bind, they do not generate an action potential, unlike acetylcholine. Therefore, neural endplate potentials do not develop. As a result, the muscle remains relaxed.

In this way, nondepolarizing blocker prevents muscle contraction. Nondepolarizing neuromuscular blockers can be long-acting, intermediate or short-acting. Tubocurarine, doxacurium, pancuronium, vecuronium, and pipecuronium are several nondepolarizing neuromuscular blockers.

What are the Similarities Between Depolarizing and Nondepolarizing Neuromuscular Blockers?

• Depolarizing and nondepolarizing neuromuscular blockers are two types of neuromuscular blockers that work at the neuromuscular junction.
• Both bind to Ach receptors.
• They are structural analogs of acetylcholine.
• They prevent muscle contraction and cause the relaxation of muscles.
• Moreover, they are used during surgeries.

What is the Difference Between Depolarizing and Nondepolarizing Neuromuscular Blockers?

Depolarizing neuromuscular blockers are the drugs that act as acetylcholine agonists while nondepolarizing neuromuscular blockers are the drugs that act as competitive antagonists. So, this is the key difference between depolarizing and nondepolarizing neuromuscular blockers.

Moreover, the depolarizing neuromuscular blockers allow depolarization of the muscle while the nondepolarizing neuromuscular blockers do not allow depolarization. Thus, this is another major difference between depolarizing and nondepolarizing neuromuscular blockers.

The below infographic tabulates more differences between depolarizing and nondepolarizing neuromuscular blockers.

Summary – Depolarizing vs Nondepolarizing Neuromuscular Blockers

Depolarizing and nondepolarizing neuromuscular blockers are two types of neuromuscular blocking drugs or skeletal muscle relaxants. Depolarizing neuromuscular blockers are non-competitive for the acetylcholine binding sites of the receptors. In contrast, nondepolarizing neuromuscular blockers are competitive for the binding sites in the receptors. Thus, this is the key difference between depolarizing and nondepolarizing neuromuscular blockers. Moreover, as a result of the action of depolarizing blockers, depolarization of the muscle takes place while due to the action of nondepolarizing blockers, depolarization does not occur.

Reference:

1. Gulenay, Michael, and Josephin Mathai. “Depolarizing Neuromuscular Blocking Drugs”. Ncbi.Nlm.Nih.Gov, 2020, Available here.
2. “Neuromuscular-Blocking Drug”. En.Wikipedia.Org, 2020, Available here.

Image Courtesy:

1. “Succinylcholine 1(cropped)” By Mark Oniffrey – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Doxacurium” By Fvasconcellos – Own work (Public Domain) via Commons Wikimedia