Muscle Relaxants Flashcards
Drugs used to treat Spasticity
- Baclofen
- Tizanidine
- Botulinum toxin
- Dantrolene Sodium
Drugs used to treat spasm:
- Cyclobenzaprine (flexeril)
- Chlorzoxazone (Paraflex)
- Orphenadrine (Norflex)
- Methocarbamol (Robaxin)
All spasmolytics drugs alleviate the symptoms of ____________ muscle spasms.
Localized
T/F: No one spasmolytic is better than the other
True
Onset of action and duration and duration for:
1) Chlorzoxazone
2) Cyclobenzaprine
3) Methocarbamol
4) Orphenadrine
1) 60 min, 4-6 hr
2) 60 min (12-24 hr
3) 30 min, 1-2 hr
4) 60 min, 2-4 hr
MOA of spasmolytics
Depress polysynaptic reflexes (over monosynaptic reflexes) in the spinal cord.
- Chlorzoxazone: unclear
- Methocarbamol- unclear
- Cyclobenzaprine: reduces tonic somatic motor activity influencing both alpha and gamma motor neurons.
- Ophenadrine: Anticholinergic used to treat spasms of various etiologies
What drug is pharmacologically related to tricyclic antidepressants, and like TCA is serotonergic, noadrenergic (also anticholinergic and antimuscarinic). Short term treatment of skeletal muscle spasm, not effective for the treatment of spasticity.
Cyclobenzaprine
What drug is pharmacologically related to tricyclic antidepressants and the MOA is unclear but may be due to general CNS depression. Short term treatment for muscle spasms.
Methocarbamol
Most common Side effects for Cyclobenzaprine. High dose effects as well:
Drowsiness, loss of physical coordination, anticholinergic side effects, dizziness.
-High Doses: Areflexia, flaccid paralysis, resp. depression, tachycardia, hypotension
Most common side effects of Methocarbamol
Drowsiness, loss of physical coordination, light-headedness, dizziness, DISCOLORATION of URINE.
-High doses: CNS depression, resp. depression
Causes of spasticity
- Accidental damage to brain or spinal cord
- Ischemia (stroke)
- MS
- CP
- Metabolic disease
- Adrenoleukodystrophy
- Amyotrophic lateral sclerosis
- Phenylketonuria
Goals in treating spasticity
- Reducing pain, frequency, irritating stimuli
- Improving gait, hygiene, activities of daily living, ease of care
Central acting treatment of Spasticity (Oral) and MOA:
Baclofen- GABAb receptor agonist
Tizanidine- alpha 2 adrenergic receptor agonist
Botulinum toxin
Gabapentin- act on N-type CA2+ channels to reduce neuropatic pain
Benzodiazepines: GABAa receptor agonist
Muscle acting treatment of spasticity
Dantrolene sodium (Dantrium)
Principal use of Oral Baclophen. Other uses:
to decrease spasticity caused by MS and spinal cord injury.
-Other: hiccups, neuropathic pain including trigeminal neuralgia, episodes of intense pain in face
What is intrathecal Baclofen and what are the advantages?
Pump surgically implanted under skin with catheter in intratecal space.
-Low dose, fewer side effects
Uses of intrathecal baclophen
- Cerebral palsy
- Anoxic brain injury
- MS
- Stroke
- Spinal cord injury
- Arteriovenous malformation
- Infection of spinal cord
MOA of baclophen
Binding to pre-synaptic GABAb receptors
a. CA2+ influx through voltage-activated channels of type I a presynaptic terminals is inhibited
- Release of glutamate and aspartate are suppressed
b. Binding to post synaptic GABAb receptors causes:
- activation of K+ channels through a membrane-delimited pathyway
- Activation of 2nd messenger pathway involving arachidonic acid
c. Reduces substance P release from nociceptive afferent nerve terminals
What is Tizanidine used for?
To decrease spasticity in patients with:
- MS
- Spinal cord injury
What drug is this: Central acting at alpha 2 adrenergic agonist. Inhibits release of excitatory amino acids in spinal interneurons.
Tizanidine
What drug is this: Used to treat spasticity caused by cerebral palsy, stroke, traumatic brain injury and advanced MS. Also treat patients with dystonia (oromandibular, cervical, laryngeal) and to treat excessive sweating.
Botulinum Toxin
MOA of Botulinum toxin. Onset of muscle paralysis, max effect, and duration of paralysis.
Inhibits acetylcholine release from pre-synaptic nerve terminals, causing chemodenervation.
-Onset of focal muscle paralysis begins in 24 to 72 hours.
-Max effect in 5 to 14 days.
-Muscle paralysis can last 12-16 weeks.
Antibodies can develop lowering efficacy
When is Botulinum toxin contraindicated
Excess weakness may result. Muscle paralysis may not be exact because toxin cannot be entirely contained.
What drug is used to treat spasticity in patients with Upper motor neuron lesions, decrease spasticity in patients with strokes and spinal cord injuries, treat malignant hyperthermia, and treat neuroleptic malignant syndrome.
Dantrolene Sodium
What Drug is this: Acts preferentially on fast muscle fibers to block muscle contraction. Reduces the depolarization-induced release of Ca2+ from the sarcoplasmic reticulum.
Dantrolene sodium
Dantrolene sodium reaches peak concentration after ________ hour(s) following oral administration and is metabolized largely by ________, t1/2=15 hours
3-6 hours, the liver
Contraindications of dantrolene sodium
Causes muscle weakness and may worsen overall functional capacity of the patient.
-SHOULD NOT BE used in patients with Amyotrophic lateral sclerosis where there is a low tolerance for muscle weakness.
Adverse effect for Baclofen
Muscle weakness, sedation, fatigue, dizziness, nausea
Adverse effects for Tizanidine
Drowsiness, dry mouth, dizziness, reversible dose-related elevation in liver transaminases.
Adverse effect for Dantrolene
Hepatotoxicity, weakness, sedation, diarrhea
Monitoring for Baclofennd special attention
Periodic liver function tests. Abrupt cessation associated with seizures.
Monitoring and special attention for tizanidine
Periodic liver fxn tests. Not to be used with antihypertensives or clonidine.
Monitoring and special attention for Dantrolene
Periodic liver fxn tests. Hepatotoxicity.
