Neuromuscular blockers (Peripheral muscle relaxants)
Neuromuscular blocking agents are mostly nicotinic blockers. They are used to induce muscle relaxation, particularly during surgical procedures and mechanical ventilation.
Classification
- Non-Depolarizing Drugs:
- Vecuronium: A commonly used intermediate-acting non-depolarizing agent that is often preferred in elective surgeries.
- Rocuronium: A fast-acting non-depolarizing agent with a moderate duration of action, often used for rapid sequence intubation.
- Pancuronium: Long-acting non-depolarizing drug, rarely used due to its cardiovascular side effects.
- Atracurium: A non-depolarizing agent that undergoes Hofmann elimination, making it useful in patients with liver or kidney impairment.
- Depolarizing:
- Succinylcholine: The only depolarizing neuromuscular blocker in clinical use. It causes initial depolarization of the muscle, leading to muscle fasciculations, followed by paralysis. It has a very short duration of action, making it ideal for procedures like rapid sequence intubation.
Pharmacodynamics
- Non-Depolarizing Neuromuscular Blockers: These drugs act as competitive antagonists at nicotinic acetylcholine receptors located on the motor endplate of the neuromuscular junction. By binding to these receptors, they prevent acetylcholine (ACh) from attaching and activating them, which inhibits depolarization of the muscle membrane and blocks muscle contraction. This competitive inhibition can be overcome by increasing the concentration of acetylcholine, such as with the administration of acetylcholinesterase inhibitors (e.g., neostigmine).
- Succinylcholine: Succinylcholine causes an initial phase of muscle fasciculations followed by paralysis. It works by binding to the nicotinic acetylcholine receptor and causing prolonged depolarization, which initially causes muscle contractions (fasciculations), followed by paralysis. It is commonly used for rapid sequence intubation due to its quick onset and short duration of action, typically lasting 5 to 10 minutes.