This document discusses muscle relaxants, including how they work, types (depolarizing and nondepolarizing), examples of commonly used drugs, their mechanisms of action, clinical uses, monitoring, and reversal with anticholinesterases. It explains that muscle relaxants block nerve impulses to muscles, are often used during anesthesia but do not affect consciousness. The main types are depolarizing drugs like succinylcholine and nondepolarizing drugs like vecuronium and atracurium, which work by competing with acetylcholine at motor nerve endings.

1. Skeletal muscle
relaxant
Laith Alasadi

2. Muscle relaxants
 Muscle relaxants are medicines that block
cholinergic transmission of nerve impulses to
the muscles.
( motor nerve ending and NM end plate of
skeletal muscle )
 They sometimes are also referred to as
neuromuscular blocking agents.

3. These medicines are often used during
anesthesia but do not usually affect
consciousness and do not provide pain
relief (analgesia).
Muscle relaxants must not be given
without adequate dosage of analgesic
and hypnotic drugs
patient is paralyzed but not
anesthetized

4. Muscle Relaxants
What are they used for?
Facilitate intubation of the
trachea
Optimized surgical working
conditions

5. Muscle Relaxants
How do they work?
 Neuromuscular junction
 Nerve terminal
 Motor endplate of a muscle
 Synaptic cleft
 Nerve stimulation
 Release of Acetylcholine (Ach)
 Postsynaptic events

8. Binding of Ach to receptors on muscle end-plate

9. Muscle Relaxants
Depolarizing muscle relaxant
Succinylcholine
Nondepolarizing muscle
relaxants
Short acting
Intermediate acting
Long acting

11. Depolarizing Muscle Relaxant
 Succinylcholine (mechanism of action )
 These drugs are structural analogue of acetylcholine .
 Physically resemble Ach
 Act as acetylcholine receptor agonist
 Not metabolized locally at NMJ
 Metabolized by pseudocholinesterase in plasma
 Depolarizing action persists > Ach
 Continuous end-plate depolarization causes muscle
relaxation

12. Depolarizing Muscle Relaxant
 Succinylcholine
What is the clinical use of
succinylcholine?
 Most often used to facilitate intubation
What is intubating dose of
succinylcholine?
 1-1.5 mg/kg
 Onset 30-60 seconds, duration 5-10 minutes

13. Depolarizing neuromuscular blockers
such as succinylcholine produce
prolonged depolarization of the end-
plate region that results in (1)
desensitization of nAChR
 The end result is failure of action
potential generation

14. Depolarizing Muscle Relaxant
 Succinylcholine side effect :
Cardiovascular
Muscle pain
Increase intraocular pressure
Increase intragastric pressure
Increase intracranial pressure
Hyperkalemia
Malignant hyperthermia

15.  In patients with normal butyrylcholinesteras
(also known as plasma cholinesterase or
pseudocholinesterase) activity, recovery to
90% muscle strength after the administration
of 1 mg/kg succinylcholine requires from 9 to
13 minutes.
 The short duration of action of succinylcholine
is due to its rapid hydrolysis by
butyrylcholinesterase.

16. Nondepolarizing Muscle
Relaxants
Mechanism of action
 Compete with Ach at the binding sites
 Do not depolarized the motor endplate
 Act as competitive antagonist
 Excessive concentration causing channel
blockade
 Act at presynaptic sites, prevent movement of
Ach to release sites

17. curare
 Hunters of Amazon in South Africa
 Poisoned arrow
 the drug was purified and introduced into
clinical practice in 1940

18. Nondepolarizing Muscle
Relaxants
 Pancuronium
 Aminosteroid compound
 Onset 3-5 minutes, duration 60-90 minutes
 Intubating dose 0.08-0.12 mg/kg
 Elimination mainly by kidney (85%), liver
(15%)
 Side effects : hypertension, tachycrdia,
dysrhythmia,

19. Nondepolarizing Muscle
Relaxants
 Vecuronium
 Analogue of pancuronium
 shorter duration than pancuronium
 Onset 3-5 minutes duration 20-35 minutes
 Intubating dose 0.08-0.12 mg/kg
 Elimination 40% by kidney, 60% by liver

20. Nondepolarizing Muscle
Relaxants
 Atracurium
 Metabolized by
 Ester hydrolysis
 Hofmann elimination
 Onset 3-5 minutes, duration 25-35 minutes
 Intubating dose 0.5 mg/kg
 Side effects :
 histamine release causing hypotension, tachycardia,
bronchospasm
 Laudanosine toxicity

21. Nondepolarizing Muscle
Relaxants
 Cisatracurium
 Isomer of atracurium
 Metabolized by Hofmann elimination
 Onset 3-5 minutes, duration 20-35 minutes
 Intubating dose 0.1-0.2 mg/kg
 Minimal cardiovascular side effects

22. Nondepolarizing Muscle
Relaxants
 Rocuronium
 Analogue of vecuronium
 Rapid onset 1-2 minutes, duration 20-35
minutes
 Onset of action similar to that of succinylcholine
 Intubating dose 0.6 mg/kg
 Elimination primarily by liver, slightly by kidney

23. Alteration of responses
 Temperature
 Acid-base balance
 Electrolyte abnormality
 Age
 Concurrent diseases
 Drug interactions

24. Monitoring Neuromuscular
Function
What are the purposes of
monitoring?
 Administer additional relaxant as indicated
 Demonstrate recovery

25. Monitoring Neuromuscular
Function
How to monitor?
 Clinical signs
 Use of nerve stimulator

26. Antagonism of Neuromuscular
Blockade
Effectiveness of anticholinesterases
depends on the degree of recovery
present when they are administered
 Anticholinesterases
 Neostigmine
 Onset 3-5 minutes, elimination half life 77
minutes
 Dose 0.04-0.07 mg/kg
 Pyridostigmine
 Edrophonium

27. Antagonism of Neuromuscular
Blockade
mechanism of action
Inhibiting activity of
acetylcholineesterase
More Ach available at NMJ, compete
for sites on nicotinic cholinergic
receptors