Muscle relaxants Flashcards
What are the clinical uses of muscle relaxants?
4
(1) General anesthesia
(2) Alignment of fractures
(3) Artificial ventilation
(4) Symptomatic treatment of convulsion or spasticities (laryngospasm)
What are the three components of the peripheral neuromuscular system?
(3)
(1) Motor nerve axon
(2) Motor nerve terminal
(3) Muscle endplate
What compounds block sodium channels to prevent motor nerve action potentials?
(2)
(1) Tetrodotoxin from puffer fish
(2) Saxitoxin from Red Tide/dinoflagellates
What compounds act at the motor nerve terminal?
2
(1) Botulinum and tetanus toxins - enzymatically cleave SNARE proteins essential to exocytosis
(2) Hypocalcemia or Ca2+ channel-blocking drugs (prevent fusion of neurotransmitter vesicle with cell membrane)
What are the are two antidotes for anticholinesterases?
2
(1) Atropine
(2) Pralidoxime
What are common properties of drugs that act on the muscle endplate Ach receptor?
(6)
(1) Must block 90% or more of AchRs to paralyze muscle fiber due to high safety factor
(2) Danger of respiratory paralysis
(3) Block nicotinic AchR of autonomic ganglia
(4) Quaternary amines with positive charge (not absorbed orally)
(5) Do not enter CNS
(6) Cleared by kidney and liver metabolism
How can competitive block of AchR be overcome?
Increasing Ach level through neostigmine use (allows patient to overcome paralysis)
What are the three groups of competitive blockers?
3
Based on structure:
1) Curare and semisynthetic alkaloids
(2) Benzylisoquinolines (Mivacurium
(3) Steroids (Pancuronium and rocuronium)
What is curare and what are its characteristics?
4
(1) Competitive neuromuscular blocker
(2) Fast on- and offset of action
(3) Little or no histamine release
(4) Little or no ganglionic blockade
What is mivacurium and what are its characteristics?
5
(1) Benzylisoquinoline competitive neuromuscular blocker
(2) Little muscarinic AchR block
(3) Little ganglionic AchR block
(4) Metabolized by cholinesterase, so short duration of action
(5) Good substitute for succinylcholine
What is pancuronium and what are its characteristics?
4
(1) Steroid neuromuscular blocker
(2) Blocks muscarinic AchR (causes tacchycardia)
(3) Long duration
(4) More potent than curare
What is rocuronium and what are its characteristics?
3
(1) Steroid neuromuscular blocker
(2) Less muscarinic AchR block than pancuronium
(3) Fast on- and offset of action - good substitute for succinylcholine
What can be used to bind rocuronium to terminate its action?
Suggamedex
What is succinylcholine?
5
(1) Depolarizing agent
(2) Similar to other competitive neuromuscular blockers, has affinity for muscle AchR
(3) Has intrinsic activity for AchR - maintains depolarized state of muscle
(4) Has two phases of block
(5) Stimulates autonomic ganglia and cardiac muscarinic AchR
What are the two phases of block by succinylcholine?
2
(1) Phase I - depolarization block (succinylcholine binds AchR and prevents repolarization)
(2) Phase II - desensitization block (AchR less sensitive to Ach, hard to depolarize)
