Skeletal Muscle Relaxants

Question 1

Cisatracurium

Answer 1

Isoquinolone derivative – competitive antagonist of ACh

Use: skeletal muscle relaxation during surgery (reduces required depth of anesthesia); muscular manifestations of epilepsy, intubation, prevent injury during ECT

PK: renal excretion, longer acting

CI: NM blockade is enhanced by myasthenia gravis, inhaled anesthetics, aminoglycosides

Question 2

Atracurium

Answer 2

Isoquinolone derivative – competitive antagonist of ACh

Use: skeletal muscle relaxation during surgery (reduces required depth of anesthesia)

PK: inactivated by spontaneous breakdown; metabolite can cause seizures at high conc

Tox: seizure, hypotension (His release), cardiac arrhythmia (M2 blockade)

Question 3

Tubocurarine

Answer 3

Isoquinolone derivative – competitive antagonist of ACh

Use: skeletal muscle relaxation during surgery

PK: renal excretion, longer acting

Tox: hypotension and bronchoconstriction (His release)

Question 4

Mivacurium

Answer 4

Isoquinolone derivative – competitive antagonist of ACh

Use: skeletal muscle relaxation during surgery

PK: metabolized by plasma psuedocholinesterase

Tox: hypotension and bronchoconstriction (His release)

Question 5

Doxacurium

Answer 5

Isoquinolone derivative – competitive antagonist of ACh

Use: skeletal muscle relaxation during surgery

PK: renal excretion, longer acting

Question 6

Pancuronium

Answer 6

steroid derivative – competitive ACh antagonist

Use: skeletal muscle relaxant during surgery

Tox: hypotension, bronchosonstriction, cardiac arrhythmias

PK: biotransformed in liver, shorter-acting

Question 7

Pipecuronium

Answer 7

steroid derivative – competitive ACh antagonist

Use: skeletal muscle relaxant during surgery

PK: biotransformed in liver, shorter-acting

Question 8

Rocuronium

Answer 8

steroid derivative – competitive ACh antagonist

Use: skeletal muscle relaxant during surgery

PK: biotransformed in liver, shorter-acting

Question 9

Vecuronium

Answer 9

steroid derivative – competitive ACh antagonist

Use: skeletal muscle relaxant during surgery

PK: biotransformed in liver, shorter-acting

Question 10

Succinylcholine

Answer 10

MOA: depolarizing agent; causes massive activation and ACh receptors leading to desensitization and closure

Use: skeletal muscle relaxation

Toxicity

• hyperkalemia in patients with burns, nerve damage, NM disease, head trauma
• increased intraocular pressure
• muscle pain
• increased intra-gastric pressure (lead to emesis and aspiration)

PK: metabolized by plasma psuedocholinesterase; short acting (<8min)

Interaction:

• arrhythmia when co-admin with halothane
• malignant hyperthermia when co-admin with halogenated anesthetics

Question 11

Baclofen

Answer 11

MOA: promotes K+ channel activity in the CNS through interaction with GABA-B receptor

Use: reduce skeletal muscle spasms in neurological disorders

Tox: hypotension, dizziness, fatigue, depression

Question 12

Diazepam

Answer 12

MOA: binds to GABA-A receptor and potentiates the action of GABA

Use: reduce skeletal muscle spasms in neurological disorders

Question 13

Tizanidine

Answer 13

MOA: unknown, a2 agonist?

Use: reduce skeletal muscle spasms in neurological disorders

Question 14

Dantrolene

Answer 14

MOA: binds to Ca2+ channel and decreases Ca2+ release from the SR

Use: reduce skeletal muscle spasms in neurological disorders; malignant hyperthermia treatment

Tox: weakness, drowsiness, diarrhea, seizure, hepatotoxicity with chronic use

Question 15

Botulinum toxin

Answer 15

MOA: blocks ACh release by interfering with synaptic vesicle exocytosis

Use: strabismus, muscles suffering from repetitive use, cosmetic

Tox: flu-like illness, gallbladder dysfunction