Skeletal muscle relaxants (USMLE)

These drugs usually are used during surgical procedures. Neuromuscular blockers acts on skeletal muscle nicotinic cholinergic receptors.

1) Nondepolarizing  neuromuscular blockers

Intermediate duration neuromuscular blockers                                                                                                              
a) atracurium ,  cisatracurium - they are safer in renal & hepatic disease, with spontaneous elimination                               
b) rocuronium,vecuronium - hepatic elimination  
 

Long duration neuromuscular blockers (renal elimination)  
a) doxacurium
b) pancuronium (blocks muscarinic receptors)
c) d-Tubocurarine (blocks autonomic ganglia and causes histamine release)

Short duration neuromuscular blocker
mivacurium

2) Depolarizing neuromuscular blockers
phase 1 of blocking - depolarizing - fasciculations, flaccid paralysis,
phase 2 of blocking - desensitization - reversed by AChE inhibitors.
Succinylcholine has ultrashort duration, stimulates autonomic ganglia & muscarinic receptors, causes Hyperkalemia and postoperative muscle pain.

3) Spasmolytics

They enhance the level of inhibition or reduce the level of excitation.

• baclofen (GABAb receptor agonist, action is in CNS) - spasticity of central or spinal or origin
• diazepam (potenciate GABAa receptor, action is in CNS  ) - acute muscle spasm
• tizanidine (alpha-2-receptor agonist, action is in CNS) - acute muscle spasm
• dendrolene (blocks ryanodine receptors on sarcoplasmic reticulum to prevent Ca release, action located in muscle) - malignant hyperthermia, neuroleptic malignant syndrome
• botulinum toxin (blocks ACh release, action is in muscle) - injected locally to relieve muscle spasm
• cyclobenzaprine (action is in CNS)-acute muscle spasm
• carisoprodol (action is in CNS)-acute muscle spasm
• metaxolone (action is in CNS)-acute muscle spasm