Muscle Relaxants Flashcards
Block neuromuscular transmission inducing skeletal muscle relaxation.
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Skeletal muscle relaxants
Classification of skeletal muscle relaxants ?
- Peripherally acting (neuromuscular blockers):
A. Competitive (non-depolarizing):
- Long acting: d-tubocurarine (prototype), Pancuronium
- Intermediate acting: Vecuronium, Atracurium
- Short acting: Mivacurium
B. Depolarizing: Succinylcholine (suxamethonium)
- Direct acting: Dantrolene
- Centrally acting: Baclofen, Diazepam
Neuromuscular Blockers ● Uses
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● Control convulsions, so used in electroshock therapy in psychotic patient
● Relieve tetanus and epileptic convulsion
● Facilitate endoscope procedures
● As adjuvant in general anesthesia to induce muscle relaxation
● Orthopedic surgery
Mechanism of action:
● Compete with acetyl choline at nicotinic receptors of post-junction
membrane of motor end plate.
Type of relaxant ?
Peripherally acting Competitive non-depolarizing neuromuscular blockers
Long acting Competitive non-depolarizing neuromuscular blockers
Example?
d-tubocurarine (prototype), Pancuronium
Competitive non-depolarizing neuromuscular blockers
Example? Intermediate acting
Vecuronium, Atracurium
Competitive non-depolarizing neuromuscular blockers
Example? Short acting?
Mivacurium
Competitive non-depolarizing neuromuscular blockers
Properties?
● Mostly quaternary compounds, thus not absorbed orally & given IV
● Do not cross blood brain barrier or placenta
● Do not cause analgesia or loss of consciousness
How to overcome Competitive non-depolarizing neuromuscular blockers? Mechanism? Examples ?
Competitive: action overcome by higher acetylcholine
● Acetyl cholinestrase enzyme inhibitors increase acetyl choline:
Pyridostigmine
Physostigmine
Edrophonium
● Anesthetist use them to prevent competitive neuromuscular blocker
overdose.
Which muscles are paralyzed first? And last?
Small and rapidly contracting muscles: more sensitive, paralyze first
● Respiratory muscles are last to be affected and first to recover
d-Tubocurarine
Type? Duration? Side effects ? Contraindications?
- Competitive non depoliticization
- long
- Adverse effects (release histamine causing bronchospasm & hypotension)
- Kidney failure
Type? Duration? Side effects ? Contraindications?
Pancuronium
- Competitive non depolarization
- long
- Side effects: Hypertension and tachycardia (due to norepinephrine release)
- coronary diseases and renal failure
Type? Duration? Side effects ? Contraindications?
Vecuronium
- competitive nonpolarizing
- intermediate
- Few side effects
- liver failure ( cause it metabolized by the liver )
Type? Duration? Side effects ? Contraindications? Used in?
Atracurium
- competitive non polarizing
- intermediate
- Hypotension Histamine release
- Used in liver & kidney failure
- Bronchial asthma
Type? Duration? Side effects ? Contraindications? Used in?
Mivacurium
- competitive non polarizing
- short
- histamine release = hypotension
- psuedo cholinesterase deficiency
Type? Duration? Side effects ? Contraindications? Used in?
Succinyl choline
- competitive depolarizing
- short
- Hyperkalemia -Arrhythmia -Increase intra- ocular pressure
- Cardiovascular diseases
Glaucoma Liver disease
Type? Duration? Side effects ? Contraindications? Used in?
Dantrolene
- Directly acting
- long
- few side effect
- Malignant hyperthermia ● Spastic states (spasmolytic effect) as spinal cord injury and cerebral palsy
Malignant hyperthermia
● Rare inherited condition that occurs during administration of drugs as: ?
Depolarizing neuromuscular blockers as succinylcholine
Malignant hyperthermia
Caused by?
Caused by inability to bind calcium by sarcoplasmic reticulum due to genetic defect
● This will cause increase calcium release, intense muscle spasm, and increase in body temperature (hyperthermia)
Malignant hyperthermia
Treatment?
dantrolene
Dantrolene
● Mechanism of Action: (directly acting muscle relaxant) ?
Interferes with release of calcium from its stores in skeletal muscles
sarcoplasmic reticulum ● Calcium is released from the sarcoplasmic reticulum via a specific calcium
channel (ryanodine channel) and dantrolene blocks these channels ● This inhibits contraction of muscles.
Muscle relaxants are contraindicated in this disease
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Myasthenia Gravis
Myasthenia Gravis
Treatment?
choline esterase inhibitors as pyridostigmine may be used (side effects: weakness, abdominal colic, diarrhea)
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