Chapter 10
The Muscular System and
Drug Therapy
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Chapter 10
Anatomy and Physiology of the Muscular System
Muscle Spasm and Relaxation
Other Muscle Disorders
Herbal and Alternative Therapies
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Anatomy and Physiology of the Muscular System
Muscular System and Skeletal Muscles
• Muscular system
 Is responsible for movement, posture, and body heat
 Divided into three types: skeletal, cardiac, and smooth
• Skeletal muscles
 Are connected to bones and joints by tendons
 Provide voluntary movement, such as walking,
clapping, and chewing
 Developed and enhanced through bodybuilding and
performance training
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Anatomy and Physiology of the Muscular System
Cardiac and Smooth Muscles
• Cardiac muscle
 Is found only in the heart
 Provides pump and squeeze action for heartbeat
• Smooth muscle
 Is found in the intestines and blood vessel walls
 Provides peristalsis
Movement that pushes material through tubes,
such as food through the intestines or blood flow
 Are involuntarily controlled by the autonomic nervous
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Anatomy and Physiology of the Muscular System
Types of Muscle
Under the microscope,
cardiac and skeletal
muscles appear to
have stripes called
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Anatomy and Physiology of the Muscular System
The Process of Muscle Contraction
• Nerve cells interface with muscle cells to initiate muscle
contraction in the neuromuscular junction
• Nerve cells release Ach and this neurotransmitter moves
across the synaptic cleft to stimulate muscle cell receptors
 Membrane depolarization occurs (positive and negative
electrical charges along membranes surface change)
 Sodium influx occurs causing the release of intracellular
calcium, stimulating muscle fibers to contract
 Muscle fibers then shortens and pulls on the attached
bones and joints, creating movement
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Anatomy and Physiology of the Muscular System
Neuromuscular Junction and Contraction
Muscle contraction stops when ACh is deactivated in the
synaptic cleft by acetylcholinesterase, an enzyme
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Anatomy and Physiology of the Muscular System
Drug Therapy and Muscles
• Muscle injury
 Is the most common reason for using drug therapy
 Common in the lower back (latissimus dorsi); head and
neck (trapezius); and legs (hamstring group,
quadriceps, and soleus)
• IM drug administration
 Administered to adults in the deltoid of upper arm and
the gluteus medius in buttocks
 Administered to children in the vastus lateralis (muscle
group in the quadriceps group of the legs)
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Anatomy and Physiology of the Muscular System
of the
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Anatomy and Physiology of the Muscular System
of the
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Muscle Spasm and Relaxation
Muscle Spasm and Spasticity
• Diseases and disorders of muscles relatively uncommon,
but injuries occur often at all ages
• Spasm
 Is an involuntary contraction of muscle fibers
 Occurs after muscle is inflamed from cell damage
 Can be painful
• Spasticity
 Is a condition where the muscles become rigid and
difficult to control for coordinated movement
 Caused by brain damage, spinal cord injury, multiple
sclerosis, cerebral palsy, or malignant hyperthermia
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Muscle Spasm and Relaxation
Drugs for Muscle Relaxation
• Mechanisms of Action
 Block signals from the brain and spinal cord that control
muscle contraction
 Inhibit ACh at the neuromuscular junction
 Prevent intracellular calcium release
• Are CNS depressant drugs
• Indications: all generally sedating which slows reflexes and
relaxes muscle spasms; some are used as anticonvulsants
and antianxiety agents
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Anatomy and Physiology of the Muscular System
Control and
Three ways to
block muscle
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Muscle Spasm and Relaxation
Centrally Acting Muscle Relaxants
• Indication: muscle spasms related to acute injury
• Usage: usually given for a defined amount of time (days to
weeks) until relief and healing occur
• Indications (baclofen and tizanidine): muscle spasticity
• Indications (other): give along with OTC and prescriptionstrength anti-inflammatory drugs like ibuprofen to control
pain and swelling associated with injuries
• Routes: all are oral; methocarbamol (Robaxin) and
orphenadrine citrate (Norflex) are also IM and IV; baclofen
(Lioresal) is also IT
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Muscle Spasm and Relaxation
Centrally Acting Muscle Relaxants (continued)
• Side Effects (common): sedation, drowsiness, dizziness,
fatigue, confusion, impaired judgment, and altered
• Side Effects (other): headache, nausea/vomiting, dry
mouth, blurred vision, and constipation
• Side Effects (rare): can cause serious changes in heart
function and blood pressure
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Muscle Spasm and Relaxation
Centrally Acting Muscle Relaxants: Cautions
• Do not take with alcohol
• Should not use with drugs that also cause CNS depression
 Antihistamines, opioids/ narcotic pain drugs, or other
controlled substances
• Monitor closely if taking antidepressants or antipsychotics
• Do not take with MAOIs
• Monitor closely or do not take if have heart conditions,
high blood pressure, or clotting disorders
• If skin rash or yellowing of the eyes develop, could be an
allergic reaction or liver dysfunction
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Muscle Spasm and Relaxation
Centrally Acting Muscle Relaxants: Cautions
• Tolerance and dependence can occur if taken long term
• Do not stop taking abruptly due to withdrawal symptoms
• Methocarbamol
 Can turn urine brown, black, or green
Patients should be warned of this effect
• Orphenadrine
 Should be swallowed whole, not chewed
Apply a warning label
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Muscle Spasm and Relaxation
Centrally Acting Muscle Relaxants: Cautions
• Carisoprodol (Soma)
 Requires heightened monitoring for abuse and
 Is metabolized by the liver to meprobamate
» Is an antianxiety medication and a controlled
substance with high risk for abuse
 Technicians should alert the pharmacist if patient
receives multiple refills at once or requests early refills
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Your Turn
Question 1: A technician notices that a patient often asks for
early refills of carisoprodol (Soma). What should the technician
do? Why?
Answer: The technician should alert the pharmacist because
the patient may be abusing or has an addiction to
carisoprodol. This drug is metabolized to meprobamate, an
antianxiety medication with high risk for abuse.
Question 2: How is muscle spasticity different than muscle
Answer: In spasticity, the muscles become rigid and difficult
to control for coordinated movement. A spasm is an
involuntary contraction of muscle fibers.
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Muscle Spasm and Relaxation
Locally Acting Muscle Relaxants: Botulinum
Toxin (Botox)
• Mechanism of Action: blocks release of ACh in the
neuromuscular junction
• Indications: migraine headache, spasticity, and
hyperhidrosis (excess sweating)
• Indications (most common): reduce facial lines and
 Administration: subdermal injection
 Localized muscle paralysis occurs, so lines and wrinkles
are less apparent
 Effects lasts weeks to months
 Rarely covered by insurance
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Muscle Spasm and Relaxation
Locally Acting Muscle Relaxants: Botulinum
Toxin (Botox) (continued)
• Side Effects (rare): dry mouth, headache, neck or back
pain, pain/itching at injection site, upper respiratory tract
infection, fever, and flulike symptoms
• Side Effects (severe): allergic reaction, chest pain, difficulty
swallowing or breathing, heart attack, arrhythmias, and
muscle weakness or paralysis in a larger area than where
 More likely at high doses (low doses used for cosmetic)
• Cautions: use carefully if have muscle dysfunction and
avoid deodorant for 24 hours if patient has hyperhidrosis
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Muscle Spasm and Relaxation
Direct Acting Muscle Relaxants: Dantrolene
• Mechanism of Action: blocks the intracellular release of
calcium and weakens muscle contractility
• Indications: muscle spasticity due to spinal cord injury or
cerebral palsy
• Indication (drug of choice): malignant hyperthermia, an
emergency situation
 Injectable dantrolene often in emergency drug kits in
areas where anesthesia is administered
 Technicians stock and monitor these kits
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Muscle Spasm and Relaxation
Direct Acting Muscle Relaxants: Dantrolene
(Dantrium) (continued)
• Routes: IV injection and oral (capsule)
• Dosage: 1–10 mg/kg
• Side Effects (common): drowsiness, dizziness, fatigue,
confusion, impaired judgment, altered coordination,
diarrhea, and photosensitivity
• Side Effect (long-term use): can be toxic to the liver
• Cautions: used with great caution in patients with liver
disease and can turn urine orange or red
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Muscle Spasm and Relaxation
Neuromuscular Blocking Agents
• Cause temporary paralysis
• Indications (with anesthesia): short-term muscle relaxation
 Used during endotracheal intubation, mechanical
respiration, and surgical procedures
• Are not prescribed in the outpatient setting for anyone not
on a ventilator
 Technicians in inpatient setting handle these agents
• Mechanism of Action: block ACh receptors or inhibit
breakdown of Ach allowing muscle to continuously
contract until fatigue and paralysis occur
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Muscle Spasm and Relaxation
Neuromuscular Blocking Agents (continued)
• Choice of agent depends on the length of the procedure or
the desired amount of time for ventilation
• Routes: all are IV; succinylcholine is also IM
• Side Effect: Low blood pressure and respiratory depression
should be closely monitored
• Cautions: cardiac arrest and changes in cardiac function,
especially in children; drugs are dosed individually
• Technicians should apply warning label to indicate the
drugs should be given for intubation or to ventilated
patients only
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Other Muscle Disorders
• Is a rare syndrome where muscle breakdown occurs and
toxic cell contents are released into the bloodstream
• Occurs as a serious side effect of the cholesterol-lowering
class of drugs called statins
• Symptoms may be silent but can include muscle aches and
pain, red- to brown-colored urine, and muscle weakness
• Laboratory tests are used to detect muscle enzymes (CK) in
the blood
• Acute renal failure is common; patients closely monitored
• Unexplained muscle pain or weakness should be reported
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Other Muscle Disorders
• Is a chronic muscle pain condition that is not fully
• Symptoms include musculoskeletal pain in the neck, back,
shoulders, chest, arms, and legs; fatigue;
tingling/numbness; dizziness; and mood disturbances
• Drug therapy includes duloxetine, pregabalin, and
milnacipran (Savella)
 Milnacipran (Savella)
Mechanism of Action: blocks reuptake of
norepinephrine and serotonin
Side effects and cautions similar to SSRIs and
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Other Muscle Disorders
Myasthenia Gravis
• Is an autoimmune process that attacks and destroys ACh
receptors on muscle cells in the neuromuscular junction
• Is a progressive disease that begins with muscle weakness
in face and neck and eventually impairs movement in all
• Drug therapy includes neostigmine (Prostigmin) and
pyridostigmine (Mestinon) to enhance muscle strength;
and azathioprine (Imuran) and cyclophosphamide
(Cytoxan) to slow the disease progression
 Neostigmine and pyridostigmine also used to reverse
the action of muscle relaxants in cases of overdose
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Other Muscle Disorders
Poliomyelitis (Polio)
• Is a rare infection of nerves that control the muscular
• Is nearly eradicated in U.S. and most developed countries
due to vaccine
• Remains a health threat in Africa, Asia, and South America
Muscular Dystrophy
• Is a group of genetically acquired conditions causing
muscle atrophy (shrinking) and wasting
• Can be severely debilitating and fatal
• Few drugs used to treat this condition
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Your Turn
Question 1: What is the primary purpose for administration of
botulinum toxin (Botox)?
Answer: The most widespread use of this drug is to reduce
facial lines and wrinkles.
Question 2: A patient is complaining of severe, unusual muscle
pain and weakness. The patient is taking atorvastin (Lipitor), a
statin used to lower cholesterol. What is the probable diagnosis
of this situation? What will the physician do?
Answer: The physician thinks the patient may have
rhabdomyolysis and will order laboratory tests to measure
muscle enzymes CK in the blood.
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Herbal and Alternative Therapies
• Few herbal and natural products are used for
muscular conditions
• Several herbal therapies taken for other problems can
interact with prescription muscle relaxants
 Includes St. John’s wort, valerian, and kava
 Technicians take note if patients purchase such
products along with their prescription muscle relaxants
• Spinal realignment
 Performed by a chiropractor
 Used to relieve muscular pain
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• Muscle injury is the most common reason for using drug
• Centrally acting muscle relaxants are used for muscle
• Direct acting muscle relaxants are used primarily for
muscle spasticity due to select conditions
• Botulinum toxin is an expensive cosmetic agent
• Neuromuscular blocking agents temporarily relax and
paralyze muscles during intubation and ventilation
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