Are thought to relieve muscle spasm by enhancing presynaptic inhibition of motor neurons in the CNS
Promotes presynaptic inhibition by enhancing the effects of gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter
Promotes inhibition by acting as an agonist at presynaptic alpha2 receptors
Drug selection of Centrally Acting Muscle Relaxants are based largely on what?
Prescriber preference and patient response
Muscle relaxants are not useful for treating what?
Spasticity or other muscle disorders resulting from CNS pathology with the exception of Diazepam (Valium)
CNS Depression Adverse Effects of all centrally acting muscle relaxants
Generalized depression of the CNS; Drowsiness, dizziness, and lightheadedness are common
Hepatic Toxicity Adverse Effects of some centrally acting muscle relaxants
Tizanidine (Zanaflex) and Metaxalone (Skelaxin) can cause liver damage; Chlorzoxazone (Paraflex, Parafon Forte DSC, others) can cause hepatitis and potentially fatal hepatic necrosis
Tizanidine (Zanaflex) and Metaxalone (Skelaxin) can cause
Chlorzoxazone (Paraflex, Parafon Forte DSC, others) can cause
Hepatitis and potentially fatal hepatic necrosis
Physical Dependence Adverse Effects of all centrally acting muscle relaxants
Chronic, high-dose therapy can cause this, manifesting as a potentially life-threatening abstinence syndrome if these drugs are abruptly withdrawn; Withdrawal should be done slowly
Cyclobenzaprine (Flexeril, Fexmid) and Orphenadrine (Banflex, Flexon, Norflex) Adverse Effects
Have significant anti-cholinergic (atropine-like) properties, and may cause dry mouth, blurred vision, photophobia, urinary retention, and constipation
Methocarbamol (Robaxin) Adverse Effects
May turn urine brown, black, or dark green; Patients should be forewarned of this harmless effect
Tizanidine (Zanaflex) Adverse Effects
Can cause dry mouth, hypotension, hallucinations, and psychotic symptoms
Carisoprodol (Soma) Adverse Effects
Can be hazardous to patients predisposed to intermittent porphyria, and hence is contraindicated for this group; (Porphyrins are essential for the function of hemoglobin — a protein in your red blood cells that links to porphyrin, binds iron, and carries oxygen to your organs and tissue; A rare hereditary disease in which the blood pigment hemoglobin is abnormally metabolized. Porphyrins are excreted in the urine, which becomes dark; other symptoms include mental disturbances and extreme sensitivity of the skin to light; Porphyria is a group of disorders that can cause nerve or skin problems. A porphyria that affects the skin is called cutaneous porphyria. A porphyria that affects the nervous system is called acute porphyria. The most common type of porphyria is porphyria cutanea tarda (PCT), which affects the skin)
A specific situation in which a drug, procedure, or surgery should not be used because it may be harmful to the person
Means that caution should be used when two drugs or procedures are used together. (It is acceptable to do so if the benefits outweigh the risk.)
Means that event or substance could cause a life-threatening situation. A procedure or medicine that falls under this category should be avoided
All centrally acting skeletal muscle relaxants can be administered
Methocarbamol (Robaxin) and Diazepam (Valium) can be administered
Acts within the spinal cord to suppress hyperactive reflexes involved in regulation of muscle movement; It may act by mimicking the actions of GABA on spinal neurons, yet has no direct effects on skeletal muscle
Baclofen (Lioresal) therapeutic use
Can reduce spasticity associated with multiple sclerosis, spinal cord injury, and cerebral palsy, however cannot with stroke; It does not relieve the spasticity of Parkinson’s disease or Huntington’s chorea (a hereditary disease marked by degeneration of the brain cells and causing chorea [a neurological disorder characterized by jerky involuntary movements affecting especially the shoulders, hips, and face] and progressive dementia)
Baclofen (Lioresal) decreases...
Flexor and extensor spasms and suppresses resistance to passive movement. These actions reduce the discomfort of spasticity and allow increased performance
Baclofen (Lioresal) is preferred to ... when ...
Dantrolene when spasticity is associated with significant muscle weakness
Baclofen (Lioresal) has no direct...
Muscle-relaxant action, so cannot decrease muscle strength
Most common adverse effects of Baclofen (Lioresal)
Involve the CNS and GI Tract
Baclofen (Lioresal) CNS adverse effects
CNS depressant and often causes drowsiness, dizziness, weakness, and fatigue that are most intense during the early phase of therapy and diminish with continued drug use; CNS depression can be minimized with doses that are small initially and then gradually increased
Baclofen (Lioresal) overdose can produce what?
Coma and respiratory depression; Dosages are low initially (i.e., 5 mg t.i.d.) and then gradually increased. Maintenance dose: 15-20 mg 3 to 4 times a day
Is there an antidote for Baclofen (Lioresal)?
No, so treatment is supportive
Does Baclofen (Lioresal) cause Withdrawal
Does not appear to cause physical dependence, however abrupt discontinuation has been associated with adverse reactions and stoppage should be done slowly over 1 to 2 weeks
Abrupt discontinuation of Oral Baclofen (Lioresal) adverse reactions
May cause visual hallucinations, paranoid ideation, and seizures
Reserved for patients who are unresponsive to or intolerant of oral Baclofen (Lioresal); Route of administration for drugs via an injection into the spinal canal, more specifically into the subarachnoid space so that it reaches the cerebrospinal fluid (CSF) and is useful in spinal anaesthesia, chemotherapy, or pain management applications; Average maintenance dose: 300-800 mcg/day
Abrupt discontinuation of Intrathecal (“pain pump”, giving medication directly to spinal cord) Baclofen (Lioresal) adverse reactions
May be dangerous; High fever, altered mental status, exaggerated rebound spasticity, and muscle rigidity that, in rare cases, has advanced to rhabdomyolysis (muscle breakdown), multiple organ system failure, and death
Intrathecal Baclofen (Lioresal)
Infusion system must be programmed properly and carefully monitored
Acts directly on skeletal muscle; Relieves spasm by suppressing release of calcium form the sarcoplasmic reticulum (SR), hence the muscle is less able to contract; Fortunately, therapeutics doses have only minimal effects on contraction of smooth muscle and cardiac muscle
Dantrolene (Dantrium) therapeutic uses on spasticity
Can relieve when associated with multiple sclerosis, cerebral palsy, and spinal cord injury
Dantrolene (Dantrium) suppresses spasticity by...
Causing a generalized reduction in the ability of skeletal muscle to contract
Dantrolene (Dantrium) treatment may be associated with...
A significant reduction in strength, and as a result, overall function may be reduced rather than improved
Dantrolene (Dantrium) care must be taken to ensure what?
The benefits of therapy (reduced spasticity) out-weigh the harm (reduced strength)
Dantrolene (Dantrium) therapeutic uses on malignant hyperthermia (fast rise in body temperature (fever) and severe muscle contractions when the affected person gets general anesthesia)
Whereas the heat of malignant hyperthermia is generated by muscle contraction occurring secondary to massive release of calcium from the sarcoplasmic reticulum (SR), Dantrolene (Dantrium) relieves symptoms by acting on the SR to black calcium release
A disease passed down through families that causes a fast rise in body temperature (fever) and severe muscle contractions when the affected person gets general anesthesia except nitrous oxide. This condition is not the same as hyperthermia that is due to medical emergencies such as heat stroke or infection
Dantrolene (Dantrium) for patients with malignant hyperthermia for pre-operative prophylaxis
Patients can be given Dantrolene (Dantrium) for prophylaxis 1 to 2 days prior to elective surgery
Dantrolene (Dantrium) for patients with ongoing crisis of malignant hyperthermia
Patients can be given Dantrolene (Dantrium) via IV push; Administration is repeated until symptoms are controlled or until a total dose has been given
Liver damage most serious adverse effect with an incidence of 1 in 1000 and occurrences of death; Most common in women over age 35 with liver injury being rare in children under 10 years of age
To reduce the risk of liver damage with the therapeutic use of Dantrolene (Dantrium)
Liver function tests (LFTs) should be performed at baseline and periodically thereafter; Either way, Dantrolene (Dantrium) should be administered in the lowest effective dosage and for the shortest time necessary
Other adverse effects from Dantrolene (Dantrium)
muscle weakness, drowsiness, and diarrhea are most common Side effects; Other disturbing reactions include anorexia, nausea, vomiting, and acne-like rash
Dantrolene (Dantrium) Administration
Capsules (25, 50, 100 mg) and as a powder to be reconstituted for IV injection
Action taken to prevent disease, especially by specified means or against a specified disease
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