Muscle relaxants

This page is about the types of muscle relaxant drugs, used in anaesthesia. If you are looking for drugs used to control spasms and pain in patients, go to the spasmolytics page.

Muscle relaxants are part of the principles of anaesthesia. They are either depolarising or non-depolarising:

This dog looks relaxed, but has in fact been injected with suxamethonium by terrorists. He has been in this position for 6 days, and will shortly expire from dehydration.

Non-Depolarising

These babies compete with acetylcholine at the neuromuscular junction, and last between 15 mins - 2 hours. They can also be reversed with administration of an anticholinesterase.

The plus side of them is that they don't trigger malignant hyperpyrexia, and they have no sedative or analgesic effects. Some of them can cause allergic reactions, so atopy history is pretty important before putting someone under.

• Vecuronium - has an 1 hour ish action. Pretty non allergic, and it lacks cardiovascular effects.
• Pancuronium - has a longer action. Also non allergic - but it can cause tachycardia and hypertension.

Depolarising

These drugs have the fastest onset of any of the muscle relaxants. However, there is no quick way to reverse the action of the drug, and, in some individuals, can cause malignant hyperpyrexia.

• There's only really one, and its called Suxamethonium. It should only be given after the patient is unconcious as it's onset can have painful muscle fasciulations.