Skeletal Relaxants

Question 1

SKELETAL: Anatomy

corticospinal tract - LSTT vs. AST decussate where + go where (2.2), purpose, UMN vs. LMN (2.2) + common sx, conditions (4)

reflex arc - reflex what + example, transmission (1-1-1-1=1)

Answer 1

CORTICOSPINAL ARC
- LSTT: decussate at level of pyramids; to extremities contralateral
- AST: no decussate; to trunk/axial & (B)
- voluntary movement
- UMN: brain & spine, LMN: spine & muscle; weakness
- conditions: stroke, SMA, ALS, polio

REFLEX ARC
- reflex: involuntary response to stimulus (eg. touch hot object)
- stimulus (hot object) -> spine -> motor neuron -> muscle = contract/pull away

Question 2

SKELETAL: Anatomy - Excitation Contraction Coupling

what (2=1)

GABA - what (2), 1=1=1 structure & purpose

glycine - what (1), where, purpose (2)

Answer 2

• mechanism between electrical impulse in plasma membrane (AP) & release of Ca from SR = contraction

GABA
- neurotransmitter, inhibitory
- bind to post-synaptic GABA receptors (modulate ion channels) -> hyperpolarize -> bye AP/relax muscle

GLYCINE
- inhibitory neurotransmitter at CNS
- sensory & processing

Question 3

SKELETAL: Centrally Acting - Baclofen

other name, mechanism (2=1=1) + where, inhibit (2) + purpose of 2nd

uses (4)

pharma - dose, absorb where, meta where, half life, excretion

adverse (3.5.1)

precautions - epilepsy, sudden withdrawal sx (3)

adverse: weakness & hypotension, withdrawal: HAT

Answer 3

P-CHLOROPHENYL GABA
- mechanism: inc K conductance dec Ca conductance = hyperpolarization = muscle relax
- at GABA receptors
- inhibit release of excitatory NT & substance P (inflammation & pain)

• uses: spasticity (SCI & MS), trigeminal neuralgia, tardive dyskinesia, chronic pain

pharma
- dose: 15-100mg/day
- absorb: GIT, meta: liver, half: 3-6h, excrete: renal

adverse effects
- weakness, fatigue, ataxia
- hypotension, nausea, headache, dizzy/drowsy, sedation
- teratogenicity

precautions
- epilepsy = dec seizure threshold
- sudden withdrawal = hallucination, anxiety, tachy

Question 4

SKELETAL: Centrally Acting - Diazepam

mechanism (1=2) (1=2)

uses (3)

pharma - route (2), absorb + peak, meta + using, half life (2), desmethyldiazepam (1=1=1), oxazepam (what)

adverse (3.2)

Answer 4

mechanism
- GABA = anti-convulsant, sedation
- glycine = anti-anxiety, relaxation

• uses: spasticity (cord lesion), spasm, CP

pharma
- route: oral, IV
- absorb: GIT, peak: 1-1:30h
- metabolism: hepatic microsomal enzyme system using oxidative pathway
- half life: 21-37h, desmethl half life: 48-96h
- desmethyldiazepam: more potent than parent = still exerting effect even after parent has metabolized = hangover effect
- oxazepam: immediately removed as conjugate

adverse
- dizzy/drowsy, sedation
- respiratory depression, hypotension, bradycardia

Question 5

SKELETAL: Centrally Acting - Other Relaxants

mechanism, drugs, use (1), adverse (1)

Answer 5

• mechanism: inhibit interneuron activity in spine
• drugs: eperisone, tizanidine, methocabamol, orpheradine, chlozoxazone
• use: adjunct for acute MSK pain
• adverse: less drowsy/dizzy

Question 6

SKELETAL: Direct Acting - Dantrium

main how (2)

dantrium - mechanism, use (1), adverse (4)

pharma - dose (4), actual dose, absorb amount, half life, excretion, metabolism

Answer 6

• direct acting: peripheral reflex arc & skeletal coupling

DANTROLENE NA
- mechanism: inhibit Ca release from SR
- use: severe spasticity of any etiology
- adverse: dizzy/drowsy, sedation, weakness, hepatotoxicity

pharma
- dose: 25 50 100mg oral, 20mg vial
- dose: 25-400mg/day
- absorb: 1/3 of oral
- half life: 8h
- metabolism: liver, excretion: renal