Neuromuscular Relaxants Flashcards
Where do neuromuscular relaxants act?
Neuromuscular relaxants selectively block the nicotinic receptors at the neuromuscular junction
How do Nm receptors trigger muscle contraction?
2 ACh are released and bind Nm leading to EPP which will summate into an AP that will propagate down to the T tubules and activate L-type Ca2+ channels which leads to contraction
How do non-depolarizing drugs function?
They are competitive antagonists of Nm
How do depolarizing drugs function?
They cause prolonged Nm activation and depolarization
How can non-depolarizing drugs be overcome?
Excess ACh
Do non-depolarizing cross the BBB?
No
Where is the receptor reserve the highest in?
Respiratory > Large Limbs > Fine muscles
What is the onset of the depolarizing drugs like?
They have a more rapid onset that is metabolized by plasma cholinesterase
What is the antidote for non-depolarizing drugs?
Cholinesterase inhibitors
What is the antidote for depolarizing drugs?
Phase 1 - Time
Phase 2 - Cholinesterase Inhibitors
What are the side effects of non-depolarizing drugs?
Non analgesic
Apnea
Increased HR due to muscarinic block
What are the side effects of depolarizing drugs?
Not analgesic Apnea Muscle pain fasciculations HTN Hyperkalemia
Why should Phase 2 block from depolarizing drugs be avoided?
Phase 2 causes desensitization where it re-polarizes but it cannot be depolarized again by ACh
What non-depolarizing agent is best for long procedures?
Pancuronium
What non-depolarizing agent is best for short procedures?
Mivacurium
What non-depolarizing agent is best for renal failure patients?
Rocuronium
What non-depolarizing agent is best for liver failure patients?
Pancuronium
What non-depolarizing agent is best for medium length procedures?
Vecuronium
What is the stretch reflex arc?
1a afferents excite and cutaneous internuncial afferent inhibit extrafusal efferents that stimulate skeletal muscle contraction
What is the cause of muscle spasticity?
It is due to the release from inhibition of supra spinal control with heightened alpha and gamma systems and increased activation of facilitory paths
Clonus
Reduced ability to lower calcium between stimulations due to increased frequency of stimulation leads to incomplete relaxation
What are the curare drugs?
Non-depolarizing agents
What are the spasmolytic drugs?
Baclofen
Diazepam
Tizanidine
Dantrolene
Succinylcholine effect
Depolarization blockade of muscle nicotinic receptors
Succinylcholine indication
Endotracheal intubation
Electro-convulsive shock therapy
Succinylcholine elimination
Plasma cholinesterase
Pancuronium effect
Non-depolarizing blockade of muscle nicotinic receptors
Pancuronium elimination
Renal excretion
Pancuronium indication
Adjuvant in surgical anesthesia, sp. abdominal wall relaxation & orthopedic procedures
D-tubocurarine use
Prototype - only used in lethal injection. No clinical use.
Rocuronium effect
Non-depolarizing blockade of muscle nicotinic receptors
Rocuronium elimination
Liver
Rocuronium indication
Intubation, muscle relaxation during surgery or ventilation
Mivacurium effect
Non-depolarizing blockade of muscle nicotinic receptors
Mivacurium elimination
Plasma cholinesterase
Mivacurium indication
Intubation, muscle relaxation during surgery or ventilation in pts w/ renal failure
Vecuronium effect
Non-depolarizing blockade of muscle nicotinic receptors
Vecuronium elimination
Liver metabolism and clearance, renal elimination
Vecuronium indication
Adjuvant in surgical anesthesia, sp. abdominal wall relaxation & orthopedic procedures
Baclofen target and effect
GABAb agonist
Reduces calcium influx, and therefore reduces the release of excitatory transmitters and substance P in spinal cord
Baclofen indication
Spinal Spasticity
Multiple Sclerosis
Baclofen toxicity
Drowsiness
Diazepam/Clonezapam target and effect
Facilitate GABA mediated pre- synaptic inhibition
Benzodiazepine receptor agonist
Diazepam/Clonezapam indication
Spinal Spasticity
Multiple Sclerosis
Diazepam/Clonezapam toxicity
Sedation and drowsiness
What is the function of GABA?
Reduces neuronal excitability
Tizanidine target and effect
Alpha2-adrenergic agonist
Tizanidine indication
Spinal Spasticity
Multiple Sclerosis
Tizanidine toxicity
Drowsiness
Hypotension
Dantrolene effect
Blocks calcium release from sarcoplasmic reticulum in muscle, thus interfering with excitation-contraction in the muscle fiber
Dantrolene indication
Spasticity
Malignant Hyperthermia
Dantrolene toxicity
Muscle Weakness
Sedation
What is the important alternative use of dantrolene?
Treating malignant hyperthermia as it can block ryanodine receptors
