Skeletal Muscle Relaxants Quiz Flashcards
What are skeletal muscle relaxants used to treat?
Used to treat conditions associated with hyper excitable skeletal muscle- specifically spasticity and muscle spasms
What is spasticity vs spasm?
-Spasticity: velocity dependent increase in muscle tone caused by the increased excitability of the muscle stretch reflex
-Spasms: involuntary muscle contractions
What are common symptoms of severe spasticity?
-Muscle stiffness
-Muscle spasms
-Rapid muscle contractions
-Fixed joints: contractures
-Exaggerated muscle jerks
-Pain or tightness around joints
What is the primary goal of skeletal muscle relaxants?
-Selective decrease in skeletal muscle excitability
-Decrease pain without causing a profound decrease in muscle function
What are common anti-spasticity drugs?
-Baclofen
-Dantrolene
-Tizanidine
-Botulinum toxin
-Gabapentin
-Diazepam (Benzodiazepines)
What are common spasmolytics?
-Carisoprodol (Soma)
-Cyclobenzaprine (Flexeril)
-Methocarbamol (Robaxin)
-Orphenadrine (Norflex)
What is the mechanism of Carisoprodol? What is a brand name of this drug?
-Its exact mechanism is unknown, but is believed to alter interneuronal activity in the spinal cord and descending reticular formation
-Polysynaptic inhibitor
-Decrease alpha motor neuron excitability
-Soma
What is the mechanism of Cyclobenzaprine? What is a brand name of this drug?
-Works centrally, likely by decreasing activity in the brainstem to relieve muscle spasms
-Flexeril
What is the mechanism of Methocarbamol? What is a brand name of this drug?
-Central muscle relaxant properties
-Robaxin
What is the mechanism of Orphenadrine? What is a brand name of this drug?
-Anticholinergic properties are believed to be responsible for this drugs mechanism
-Norflex
What are the key differences in the mechanisms for anti-spasticity drugs vs spasmolytics?
-Anti-spasticity drugs often have more specific targets
-Spasmolytics are less clear and can be diverse
What are the uses of polysynaptic inhibitors?
-Adjuncts to rest and PT for relief of muscle spasms associated with acute painful MSK injuries
-The same compounds sometimes incorporated into the same tablet with analgesic (Norgesic)
What are adverse effects of polysynaptic inhibitors?
-Drowsiness, dizziness
-Nausea, lightheadedness, vertigo, ataxia, headache
-Tolerance and physical dependence
What are the most common polysynaptic inhibitors?
-Carisoprodol (Soma)
-Cyclobenzaprine (Flexeril)
-Methocarbamol (Robaxin)
-Orphenadrine citrate (Norflex)
What is the mechanism of Diazepam (Valium)?
-Increases the inhibitory effects at CNS synapses that use GABA
-Binds to GABA A receptors: positive allosteric modulation
-Increases GABA-mediated inhibition of alpha motor neuron ——> less excitability
What are therapeutic uses of Diazepam?
-Treats muscle spasms associated with MSK injuries, especially low back strains
-Controls muscle spasms associated with tetanus toxin (inhibits spasms of larynx)
What are adverse effects of Diazepam?
-Sedation and a general reduction in psychomotor ability
-Long-term use also limited by tolerance and dependence
-Sudden withdrawal after prolonged use can cause seizures, anxiety, agitation, tachycardia, and even death
-Overdose can result in coma or death
What is an antidote for diazepam?
Flumazenil is antidote for Diazepam and other benzodiazepines
What drugs work on GABA A receptors?
Benzodiazepines (Valium/diazepam)
What drugs work on GABA B receptors?
Baclofen
What drugs work on alpha 2 receptors in the spinal cord?
Tizanidine
What drugs work directly on the skeletal muscle?
Dantrolene
What is the chemical name of Baclofen (Lioresal)? What is the mechanism?
-Chemical name: beta-(p-choloro-phenyl)-GABA
-Derivative of the central inhibitory GABA
-Binds to GABA B receptors in spinal cord
-Inhibits transmission within the spinal cord at specific synapses causing an inhibitory effect on alpha motor neurons within spinal cord
What are common uses of Baclofen?
-Administered orally to treat spasticity with spinal cord lesions (paraplegia, quadriplegia, SC demyelination)
-Drug of choice with MS because of fewer side effects
-Does not cause as much generalized muscle weakness as direct-acting relaxants such as Dantrolene
What are the adverse effects of Baclofen?
-Transient drowsiness which usually disappears within a few days
-Sometimes confusion and hallucinations in patients with CVA or in elderly
-Nausea, muscle weakness
-Headache
What are intrathecal injections? What are they used for? What is the benefit?
-Spinal injections
-Used in severe spasticity (Baclofen)
-Catheter and “pump” deliver drug to subarachnoid space
-May decrease spasticity with less drug, fewer systemic side effects
What is an itrathecal baclofen pump?
-Smaller catheter usually implanted surgically
-Open end of the catheter is attached to some type of programmable pump
-Pump is implanted subcutaneously in the abdominal wall
-Adjusted to deliver drug at slow, continuous rate
-Rate of infusion titrated over time to achieve best clinical reduction in spasticity
What are adverse effects of intrathecal baclofen?
-Disruption in delivery system
-Pump malfunction
-Increased drug delivery can cause overdose
-Abrupt stoppage of drug secondary to pump dysfunction can cause withdrawal syndrome (fever, confusion, delirium, seizures)
-Tolerance with long-term use
What is the mechanism of adrenergic alpha-2 receptor agonists? What is the primary agent?
-Primary agent: Tizanidine (Zanaflex)
-Stimulate alpha-2 receptors located on spinal interneurons
-Cause inhibition of interneurons which decreases excitatory input onto alpha motor neuron
-Tizanidine decreases excitability by both pre and post synaptic inhibition
-Efficacy similar to Baclofen but with less generalized muscle weakness
What are the uses of alpha-2 agonists?
-Control spasticity from spinal lesions and central lesions
-As effective in decreasing spasticity as oral baclofen or diazepam
-Milder side effects and less generalized muscle weakness
-Tizanidine is better than Clonidine because it has less cardiovascular side effects and hypotension
What are the adverse effects of alpha-2 agonists?
Sedation, dizziness, dry mouth
What is the mechanism of Gabapentin (Neurontin)?
-Calcium channel blocker
-Developed originally as anti-seizure drug
-Enhances GABA effect in spinal cord (exact mechanism unclear)
What are the uses of Gabapentin (Neurontin)?
-Decrease spasticity associated with SCI and MS
-Best use may be in combination with other anti-spasticity agents (Gabapentin + Baclofen)
-May help in reducing certain types of chronic pain
What are adverse effects of Gabapentin?
-Sedation and fatigue
-Dizziness
-Ataxia
What is the mechanism of Dantrolene (Dantrium)?
-Only direct acting muscle relaxant
-Inhibits release of calcium from skeletal muscle sarcoplasmic reticulum
What are the uses of Dantrolene?
-Effective in treating severe spasticity
-Not prescribed to treat muscle spasms caused by MSK injury
What are adverse effects of Dantrolene?
-Generalized muscle weakness most common
-Use of Dantrolene therefore can be counterproductive because increased motor function with decreased spasticity is offset by muscle weakness
-Severe hepatotoxicity and fatal hepatitis
What is the mechanism of Botulinum Toxin?
-Injected locally for severe spasms such as torticollis, laryngospasms
-Increased use in spasticity
-Inhibits release of acetylcholine at neuro-muscular junction
Where is Botulinum injected into? How long does it last? How does it help with spasticity?
-Injected into skeletal muscle
-Relaxation/paralysis occur within 3-7 days and lasts 2-3 months
-Remove spastic dominance in certain patients
-Volitional motor function can be facilitated
-Improved gait and other functional activities in patients with cerebral palsy or TBI
-Helps to stretch muscle and prevent joint contractures
-Enables patients to wear orthotic devices
What are the problems and limitations with Botulinum Toxin?
-Local irritation at injection site
-Only a limited number of muscles can be injected during a given treatment
-Must limit total dose (300-400 units of Type A, 2500-5000 units Type B)
-Exceeding recommended dosage can cause immune response which will create antibodies against toxin making subsequent treatments less effective
How do effects of Botulinum Toxin wear off?
-New presynaptic terminal sprouts from axon that originally effected by toxin
-New motor end plate with new source of acetylcholine
-Another injection needed to block sprout
What is the duration of action of carisoprodol (Soma)?
4-6 hours
What is the duration of action of chlorzoxazone?
3-4 hours
What is the duration of action of cyclobenzaprine (Flexeril)?
12-24 hours
What is the duration of action of Diazepam (Valium)?
Up to 24 hours
What is the duration of action of Metaxalone?
4-6 hours
What is the duration of action of Methocarbamol (Robaxin)?
Unknown
What is the duration of action of Orphenadrine citrate (Antiflex, Norflex)?
12 hours
What are alternatives to skeletal muscle relaxants?
-Physical therapy
-Ibuprofen/NSAIDS
-Tramadol
-Opioids
What are special concerns for rehab patients who use skeletal muscle relaxants?
-Meds are used to compliment PT interventions
-Long term use is not recommended: addiction
-PT can reduce the need for meds
-Possible drastic change in muscle tone over short period of time
-Pt’s sometimes rely on muscle spasms or spasticity for functioning
What effects of anti-spastic and spasmolytic drugs can interfere with rehabilitation?
-Motor control problems
-Functional decline for daily activities
-Decreased alertness
-Weakness
-Tolerance and physical dependence
What are possible PT solutions to effects of anti-spastic and spasmolytic drugs?
-Schedule PT for time of day when sedative effects are less marked
-Discuss with pt’s PCP
-In pt’s with spasticity due to neurological injury, use intensive PT to return pt to normal physiologic motor control
-Use intensive therapy for acute MSK injuries
-Improve muscle strength, posture, and flexibility which can decrease need for medications
