Pharmacology Exam 3 - Ch. 25 Muscle Relaxants

Direct-Acting Skeletal Muscle Relaxants #1

*Actions o Interfering with the release of calcium from the muscle tubules o This prevents the fibers from contracting o Does not interfere with neuromuscular transmission vIndications o Treatment of spasticity directly affecting peripheral muscle contraction o Management of spasticity associated with neuromuscular diseases

Centrally Acting Skeletal Muscle Relaxants #1

*Actions o Work in upper levels of CNS to interfere with reflexes causing muscle spasm o Possible depression anticipated with their use o Lyse or destroy spasm (spasmolytics) o Exact mechanism unknown, thought to involve action in upper or spinal interneurons *Indications o Alleviation of signs and symptoms of spasticity; use in spinal cord injuries or diseases

Centrally Acting Skeletal Muscle Relaxants #3

*Adverse Effects o Drowsiness o Fatigue o Weakness o Confusion o Headache o Nausea o Dry mouth o Hypotension o Urinary frequency, enuresis, and feelings of urinary urgency reportedly may occur. Chlorzoxazone may discolor the urine, becoming orange to purplish-red when metabolized and excreted. Patients should be warned about this effect to prevent any fears of blood in the urine. Tizanidine has been associated with liver toxicity and hypotension in some patients

Direct-Acting Skeletal Muscle Relaxants #4

*Adverse Effects o Fatigue o Weakness o Confusion o GI irritation o Enuresis *Drug-Drug Interactions o Estrogen o Neuromuscular junction blockers and others that interfere with neuromuscular transmission

Direct-Acting Skeletal Muscle Relaxants #3

*Contraindications o Known allergy to any of these drugs to prevent hypersensitivity reactions and with skeletal muscle spasms resulting from rheumatic disorders, which would not benefit from these drugs. o Spasticity- that contributes to locomotion, upright position, or increased function o Hepatic disease o Lactation *Cautions o Women o All patients older than 35 years o Cardiac disease

Centrally Acting Skeletal Muscle Relaxants #4

*Drug-Drug Interactions o CNS depressants o Alcohol o If any of the centrally acting skeletal muscle relaxants are taken with other CNS depressants or alcohol, CNS depression may increase. Patients should be cautioned to avoid alcohol while taking these muscle relaxants; if this combination cannot be avoided, they should take extreme precautions

Neuromuscular Abnormalities

*Muscle Spasm o Often results from injury to the musculoskeletal system o Caused by the flood of sensory impulses coming to the spinal cord from the injured area o These impulses can be passed through interneurons to spinal motor nerves, which stimulate an intense muscle contraction. The contraction cuts off blood flow to the muscle fibers in the injured area, causing lactic acid to accumulate and resulting in pain *Muscle Spasticity o Result of damage to neurons within the CNS rather than injury to peripheral structures o May result from an increase in excitatory influences or a decrease in inhibitory influences within the CNS. The interruption in the balance among all of these higher influences within the CNS may lead to excessive stimulation of muscles, or hypertonia, in opposing muscle groups at the same time, a condition that may cause contractures and permanent structural changes. This control imbalance also results in a loss of coordinated muscle activity. o The signs and symptoms of cerebral palsy and paraplegia are related to the disruption in the nervous control of the muscles. The exact presentation of any chronic neurological disorder depends on the specific nerve centers and tracts that are damaged and how the control imbalance is manifested.

Centrally Acting Skeletal Muscle Relaxants #2

*Pharmacokinetics o Rapidly absorbed and metabolized in the liver o Excreted in the urine *Contraindications o Known allergy o Rheumatic disorders *Cautions o Epilepsy o Cardiac dysfunction o Conditions marked by muscle weakness

Direct-Acting Skeletal Muscle Relaxants #2

*Pharmacokinetics o Slowly absorbed from the GI tract o Metabolized in the liver o T ½ 4-8 hours o Excreted in the urine o Baclofen is available in oral and intrathecal forms and can be administered via a delivery pump for the treatment of central spasticity. o Cyclobenzaprine is available in a controlled release oral form for continual control of the discomfort without repeated dosings. o Methocarbamol is available in both oral and parenteral forms. Most of these agents are rapidly absorbed and metabolized in the liver. Baclofen is not metabolized, but like the other skeletal muscle relaxants it is excreted in the urine.

Brain Control

*Pyramidal Tract o Controls precise intentional movements *Extrapyramidal Tract o Modulates unconsciously controlled muscle activity o Allows the body to make automatic adjustments in posture, position, and balance o controls lower level, or crude, movements. o Many are now not using the terms pyramidal and extrapyramidal tracts to describe movement since so many movements can't be clearly classified into one or the other tract.

Types of Spinal Reflexes

*Simple o Involving an incoming sensory neuron and an outgoing motor neuron *Complex o Involving interneurons which communicate with the related centers in the brain

Nerves and Movement

*Spinal Reflexes: are the simplest nerve pathways that monitor movement and posture. It can be simple, involving an incoming sensory neuron and an outgoing motor neuron, or more complex, involving interneurons that communicate with the related centers in the brain *Influences from Upper-level CNS Areas o Basal ganglia o Cerebellum o Cerebral cortex * Areas of the brainstem, the basal ganglia, and the cerebellum modulate spinal motor nerve activity and help to coordinate activity among various muscle groups, thereby allowing coordinated movement and control of body muscle motions. Nerve areas within the cerebral cortex allow conscious, or intentional, movement. Nerves within the cortex send signals down the spinal cord, where they cross to the opposite side of the spinal cord before sending out nerve impulses to cause muscle contraction. In this way, each side of the cortex controls muscle movement on the opposite side of the body

A patient experienced a musculoskeletal injury resulting in a great deal of pain in his lower back. How can the nurse augment the drugs to aid in pain relief? A. Moist cold B. NSAIDs C. Passive exercise D. Active exercise

B. NSAIDs Rationale: Provide additional measures to relieve discomfort—heat, rest for the muscle, NSAIDs, positioning— to augment the effects of the drug at relieving the musculoskeletal discomfort.

Reflex Arch Showing Pathway of Impulses

Relaxed muscle fiber -> Spindle (stretch sensor) stretches (in response to gravity) -> stimulates sensory nerve -> spinal cord -> stimulates gamma nerve .-> muscle fiber contracts -> No stretch -> Sensory nerve not stimulated -> Gamma nerve not stimulated -> Muscle fiber relaxes

7. Dantrolene is associated with potentially fatal cellular damage. If your patient's condition is being managed with dantrolene, the patient should a) have repeated complete blood counts during therapy. b) have renal function tests done monthly. c) be monitored for signs of liver damage and have liver function tests done regularly. d) have a thorough eye examination before and periodically during therapy.

c) be monitored for signs of liver damage and have liver function tests done regularly

6. The use of neuromuscular junction blockers may sometimes cause a condition known as malignant hyperthermia. The drug of choice for prevention or treatment of this condition is a) baclofen. b). diazepam. c) dantrolene. d) methocarbamol.

c) dantrolene

4. The drug of choice for a patient experiencing severe muscle spasms and pain precipitated by anxiety is a) methocarbamol. b) baclofen. c) diazepam. d) carisoprodol.

c) diazepam

1. A muscle spasm often results from a) damage to the basal ganglia. b) CNS damage. c) injury to the musculoskeletal system. d) chemical imbalance within the CNS.

c. injury to the musculoskeletal system.

2. Muscle spasticity is the result of a) direct damage to a muscle cell. b) overstretching of a muscle. c) tearing of a ligament. d) damage to neurons within the CNS.

d) damage to neurons within the CNS.

5. Dantrolene (Dantrium) differs from the other skeletal muscle relaxants because a) it acts in the highest levels of the CNS. b) it is used to treat muscle spasms as well as muscle spasticity. c) it cannot be used to treat neuromuscular disorders. d) it acts directly within the skeletal muscle fiber and not within the CNS.

d) it acts directly within the skeletal muscle fiber and not within the CNS.

3. Signs and symptoms of tetanus, which includes severe muscle spasm, are best treated with a) baclofen. b) diazepam. c) carisoprodol. d) methocarbamol.

d) methocarbamol.

Use of Muscle Relaxants Across the Lifespan - ADULTS

o Adults being treated for acute musculoskeletal pain should be cautioned to avoid driving and to take safety precautions against injury because of the related CNS effects, including dizziness and drowsiness. Rest of the muscle, heat, massage, physical therapy are key components to recovery from any muscular injury or pain. o Adults complaining of muscle spasm pain that may be related to anxiety often respond very effectively to diazepam, which is a muscle relaxant and anxiolytic. Women of childbearing age should be advised to use contraception when they are taking these drugs. If a pregnancy does occur, or is desired, they need counseling about the potential for adverse effects. o Women who are nursing should be encouraged to find another method of feeding the baby because of the potential for adverse drug effects on the baby. Premenopausal women are also at increased risk for the hepatotoxicity associated with dantrolene and should be monitored very closely for any change in hepatic function and given written information about the prodrome syndrome that often occurs with the hepatic toxicity.

Key Points

o Movement and muscle control are regulated by spinal reflexes and the upper CNS, including the basal ganglia, cerebellum, and cerebral cortex. o Spinal reflexes can be simple, involving an incoming sensory neuron and an outgoing motor neuron, or more complex, involving interneurons that communicate with the related centers in the brain. o The pyramidal tract in the cerebellum coordinates intentional muscle movement, and the extrapyramidal tract in the cerebellum and basal ganglia coordinates involuntary muscle activity. o Muscle or skeletal damage may send a multitude of stimuli to the spinal cord and result in muscle spasms or extended contraction. o Damaged motor neurons can cause muscle spasticity and impaired movement and coordination. o The centrally acting skeletal muscle relaxants interfere with the reflexes that are causing the muscle spasm. o The centrally acting skeletal muscle relaxants cause CNS depression, and the adverse effects associated with them are related to the CNS depression (insomnia, dizziness, confusion, anticholinergic effects). o The centrally acting muscle relaxants are used for the relief of discomfort associated with acute, painful musculoskeletal conditions as an adjunct to rest, physical therapy, and other measures

Use of Muscle Relaxants Across the Lifespan - OLDER ADULTS

o Older patients are more likely to experience the adverse effects associated with these drugs—CNS, GI, and cardiovascular. Because older patients often also have renal or hepatic impairment, they are also more likely to have toxic levels of the drug related to changes in metabolism and excretion. o Carisoprodol is the centrally acting skeletal muscle relaxant of choice for older patients and for those with hepatic or renal impairment. If dantrolene is required for an older patient, lower doses and more frequent monitoring are needed to assess for potential cardiac, respiratory, and liver toxicity. o Older women who are receiving hormone replacement therapy are at the same risk for development of hepatotoxicity as premenopausal women and should be monitored accordingly.

Use of Muscle Relaxants Across the Lifespan - CHILDREN

o The safety and effectiveness of most of these drugs have not been established in children. If a child older than 12 years of age requires a skeletal muscle relaxant after an injury, metaxalone has an established pediatric dosage. o Other agents have been used, with adjustments to the adult dosage based on the child's age and weight. Baclofen is often used to relieve the muscle spasticity associated with cerebral palsy. A caregiver needs intensive education in the use of the intrathecal infusion pump and how to monitor the child for therapeutic as well as adverse effects. o Methocarbamol is the drug of choice if a child needs to be treated for tetanus. o Dantrolene is used to treat upper motor neuron spasticity in children. The dosage is based on body weight and increases over time. The child should be screened regularly for CNS and GI (including hepatic) toxicity. o Botulinum toxins are not approved for use in children. The use of these neurotoxins in children has been associated with the development of botulism