Page 58 - pharma 1 theoretical updated MNU_Neat

Clinical pharmacy 2024/2025 Level 3 Pharm D Pharmacology 1 (PO 502)

 Skeletal muscle relaxants (neuromuscular blockers)

Drugs interfere with neuromuscular transmission.
➢ Act pre-synaptically (drugs interfere with synthesis &/or release of Ach).
➢ Post-synaptically.

Postsynaptic neuromuscular blockers (NMBs) are classified into:
Competitive Non-competitive
Class
(Non-depolarizing) NMBs: (Depolarizing) NMBs:
1) Their action involves 2 phases:

2) Phase I ➔ bind to nicotinic receptors ➔
Depolarization ➔ succinylcholine is not

Compete with Ach at the rapidly hydrolyzed ➔ maintained
nicotinic receptor site ➔ depolarization.
MOA e.g. 3) Phase II ➔ maintained depolarization ➔
 D-tubocurarine desensitization of nicotinic receptors (not

 pancuronium respond to Ach).
 As succinylcholine (suxamethonium)
 decamethonium.

 Skeletal muscles:  Skeletal muscle:

➢ Motor weakness & ➢ Transient fasciculations followed by
muscles become paralysis ➔ affects arms, neck & legs
unexcitable to stimulation. before facial & pharyngeal muscles &

➢ Muscles capable of rapid lastly respiratory muscles.
movements as jaw & eye ➢ Muscles pain may follow administration
are paralyzed before larger of succinylcholine ➔ due to damage

muscles of limbs & trunks produced by contraction of adjacent
& lastly the diaphragm is muscles fibers.
paralyzed.  Cardiovascular system:

Actions: ➢ The effect lasts 30-60 ➢ Bradycardia & arrhythmias ➔ due to
min. activation of cholinergic receptors in
➢ Recovery occurs in the heart & autonomic ganglia.
reverse order. ➢ Succinylcholine-induced hyperkalemia

 Cardiovascular system: Especially in patients with severe burns,

➢ Causes hypotension ➔ closed head injury, nerve damage & renal
due to liberation of failure.
histamine & in large ➢ Transient elevation of IOP:
doses from ganglionic ➢ Succinylcholine has short duration of

blockade. action (About 10 minutes) due to its rapid
hydrolysis by pseudo cholinesterase.

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