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Flashcards in Muscle Relaxers Or Spasmolytics Deck (14)
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Spasmolytics or muscle relaxers can act...

Centrally or in the periphery (direct acting). Botox, and Dantrolene are the only agents that act in the periphery.


Spasmolytic or muscle relaxer uses
Use when we want to control at the level of the nervous system to decrease firing of neuron

Musculoskeletal conditions causing pain &spasms ( fibromyalgia, tension headaches, myofacial pain syndrome, and chronic/acute back and neck pain)
Increased spasticity or tonic stretch reflexes (spinal cord injury, cerebral palsy, stroke, multiple sclerosis)


Drugs that target spasticity
Or hyperexcitation of motor neurons

Baclofen (Lioresal)
Tizanidine (Zanaflex)
Diazepam (Valium)
Dantrolene (Dantrium)-->Dr. Ha doesn't mention


Drugs that target musculoskeletal conditions with spasms (acute spasmolytic conditions)
Decrease inappropriate muscle firing out of brain, decrease inappropriate muscle contraction
All except one have abuse potential

Carisoprodol (Soma)
Chlorzoxazone (Paraflex or Parafon Forte DSC)
Cyclobenzaprine (Flexeril or Amrix)
Metaxolone (Skelexin)
Methocarbamol (Robaxin)
Orphenadrine citrate (Norflex)
Tizanidine (Zanaflex) no abuse potential -->Dr. Sharpe doesn't include


Baclofen (Lioresal)

GABA B receptor (metabotropic receptor) agonist
GABA analog
Inhibits neurotransmission by hyperpolarizing cell preventing motor neuron from firing. Can also work in pre synaptic cell inhibiting NT release/firing
Inhibit substance P (pain) release in spinal cord
ADR: hypotension, dizziness/drowsiness, sedation


Carisoprodol (Soma)

Musculoskeletal conditions with spasms
Centrally acting as a depressant
Substituted alkanediol
Metabolized via CYP2C19 to meprobamate (soma molecule without propyl group)
Both parent drug and metabolite are active
DDI: CYP2C19 inducers/inhibitors
ADR: sedation/ drowsiness, anxiolytic, abuse potential


Chlorzoxazone (Paraflex or Parafon Fortes DSC)

Musculoskeletal conditions with spasms
Centrally acting as a depressant
Idiosyncratic hepatotoxicity
Sensitivity rxns (urticaria, erythema, pruritus)
ADR: sedation/drowsiness. Abuse potential


Cyclobenzaprine (Flexeril or Amrix)

Musculoskeletal conditions with spasms
Centrally acting as a depressant
Tricyclic antidepressant
Food increases BA b/c drug is lipophilic. Long plasma T1/2=1-3days
Accumulates on multiple dosing and causes high incidence of sedation b/c of slow elimination
ADR: sedation/drowsiness. Abuse potential


Diazepam (Valium)

GABA A receptor (ionotropic receptor): hyperpolarizes cell keeping motor neuron from firing
CYP2C19/CYP3A4 metabolizes to active metabolites. N-desmethyl diazepam has long terminal T1/2 life
ADR: hypotension, sedation, dizziness/drowsiness, abuse potential, and rebound/withdrawal syndrome(opposite effects=> HTN, anxiety, insomnia. Don't D/C abruptly)


Metaxolone (Skelexin)

Musculoskeletal conditions with spasms
Centrally acting as a depressant
Substituted alkanediol
High Vd(800L), lipophilic drug, fatty food increases BA
ADR: sedation/drowsiness (less sedation, decreased abuse potential compared to other centrally acting depressants)


Methocarbamol (Robaxin)

Musculoskeletal conditions with spasms
Centrally acting as a depressant
Glycerol monoether derivative
R-(+) enatiomer is more active
DDI: May inhibit pyridostigmine effects (AChE inhibitor). Use with caution in myasthenia gravis patients receiving AChE inhibitors to increase their muscle strength/contractions.
ADR: sedation/drowsiness, abuse potential


Orphenadrine (Norflex)

Musculoskeletal conditions with spasms
Centrally acting as a depressant
Ethanolamine ether
Related to H1 antagonist diphenhydramine HCL
MOA: possibly anticholinergic or NMDA antagonist
ADR: sedation/drowsiness, abuse potential, anticholinergic effects( dry mouth, urinary retention, blurred vision)


Tizanidine (Zanaflex)

Musculoskeletal conditions with spasms OR Spasticity
Alpha-2 adrenergic receptor agonist (centrally acting)
Alpha-2(cns)coupled to Gi=> decrease AC, cAMP, Ca+=> decrease NT release
Works at pre synaptic neuron (autoreceptor) to decrease release of excitatory AA glutamate and aspartate. Decrease presynaptic firing
Structurally similar to clonidine
Extensive 1st pass metabolism by CYP1A2
DDI: inhibitors of CYP1A2(Ex: amiodarone, fluvoxamine)
ADR: drowsiness/sedation, hypotension, dry mouth, muscle weakness (from decreased firing)


Dantrolene (Dantrium)

Spasticity or hyperexcitation of motor neurons
Direct acting: acts on skeletal muscle on ryanodine receptor (RyR1), decrease Ca+ release, and thus force of contraction
Only spasmolytic (besides Botox) that works at the level of the muscle. It can cross BBB to give CNS effects b/c 50% unionized at physiologic pH
Treatment of malignant hyperthermia by decreasing temperature
Hydantoin derivative
ADR: sedation, muscle weakness