Neuromuscular Relaxants

Question 1

Non-depolarizing agents

Answer 1

ie curare
Competetive antagonism of Nm receptor
Can be overcome by excess Ach
Channel pore blockade at higher concentrations

Do not cross BBB
Clearance: renal (slow) > hepatic (faster) > plasma cholinesterase (fast)

Question 2

Non-depolarizing agents

Pharmacokinetic data

Answer 2

Half-lives (from shortest to longest)
Mivacurium
Rocuronium
Vecuronium
Pancuronium
Tubocurarine

Question 3

Receptor reserve/ order of onset of effects

Answer 3

Face -> limbs -> respiratory muscles

Question 4

Clinical use of non-depolarizing NM relaxants

Answer 4

Adjuvent to anesthesia
Relaxation of larynx for endotracheal intubation
Relaxation of chest during mechanical ventilation

Question 5

NM relaxants

Side effects

Answer 5

Not analgesic (all)
Apnea (all)
Histamine release (mivacurium)
Muscarinic blockade: increased HR and CO (pancuronium, rocuronium)

Question 6

NM relaxants

Drug interactions

Answer 6

Inhalation anesthetics (enhance effect)
Antibiotics (enhance effect, particularly aminoglycosides)

Question 7

NM relaxants

Antidote

Answer 7

Cholinesterase inhibitors - neostigmine

given with Muscarinic blocker (to minimize effect of cholinesterase inhibitor) - glycopyrrolate

Question 8

Depolarizing agents

Phase I

Answer 8

Depolarization of muscle with sustained contractions (opens cation channel to cause EPP)
Flickering of channel due to blockade of channel
Flaccid paralysis
Cholinesterase inhibitors augment block

Question 9

Depolarizing agents

Phase II

Answer 9

Desensitization block
Membrane becomes repolarized
Receptor becomes insensitive to Ach (and other agonists)
Resembles non-depolarizing blockade (can be overcome by cholinesterase inhibitors)

Question 10

Depolarizing agents (succinylcholine)
Pharmacokinetics

Answer 10

More rapid onset than non-depolarizing agents
Metabolized by plasma cholinesterase
Action terminated by diffusion away from synapse

Question 11

Depolarizing agents

Clinical Uses

Answer 11

Endotracheal intubation
Suppression of muscle contraction during electro-convulsive shock therapy

Fasiculations in arm, neck, legs, then diaphragm followed by flaccid paralysis

Question 12

Depolarizing agents

Side effects

Answer 12

Not analgesic (all)
Apnea (all)
Muscle pain (fasciculations)
Intraocular pressure/intragastric pressure
Stimulation of ganglionic nicotinic receptors (arrythmia and hypertension)
Stimulation of muscarinic receptors, sinoatrial node (bradycardia)
Hyperkalemia (K+ release from motor endplate), immediately after burns, several days after widespread tissue injury

Question 13

Depolarizing agents

Drug interactions

Answer 13

Local anesthetics
Cholinesterase inhibitors (enhance effects of phase I block)

Question 14

Depolarizing agents

Antidotes

Answer 14

Phase I: Time for diffusion away from synapse and hydrolysis by plasma cholinesterase

Late Phase II: Cholinesterase inhibitors

Question 15

Depolarizing agents

Contraindications

Answer 15

Family history of malignant hyperthermia
Burns (early)
Major soft tissue injury (delayed)
Skeletal muscle myopathies

Question 16

Spasmolytic Drugs

Answer 16

Indications- heightened skeletal muscle tone due to:

1. Release from inhibitory supraspinal control
2. Increased activity of facilitory pathways
3. Increased excitability of a and y motor systems

Question 17

Goal of spasmolytic therapy:

Answer 17

1. Reduce 1a afferent-mediated stretch reflex
2. Enahnce activity of inhibitory internuncial neurons

1a afferent excite, cutaneous afferents inhibit