2© paradigm publishing, inc. chapter 10 the muscular system and drug therapy

© Paradigm Publishing, Inc. 2

Chapter 10

The Muscular System and Drug Therapy


Chapter 10

Topics

• Anatomy and Physiology of the Muscular System• Muscle Spasm and Relaxation • Other Muscle Disorders • Herbal and Alternative Therapies


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



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 system



Types of Muscle Tissue

Under the microscope, cardiac and skeletal muscles appear to have stripes called striations



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



Neuromuscular Junction and Contraction

Muscle contraction stops when ACh is deactivated in the synaptic cleft by acetylcholinesterase, an enzyme



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)



Anatomy of the Muscular System


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



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



Muscle Control and Relaxation

Three ways to block muscle contraction



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 prescription-

strength 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



Centrally Acting Muscle Relaxants (continued)• Side Effects (common): sedation, drowsiness, dizziness,

fatigue, confusion, impaired judgment, and altered coordination

• 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



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



Centrally Acting Muscle Relaxants: Cautions (continued)• 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 greenPatients should be warned of this effect

• Orphenadrine Should be swallowed whole, not chewed

Apply a warning label



Centrally Acting Muscle Relaxants: Cautions (continued)• Carisoprodol (Soma)

Requires heightened monitoring for abuse and addiction

Is metabolized by the liver to meprobamateMeprobamate » 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


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 spasm?

Answer: In spasticity, the muscles become rigid and difficult to control for coordinated movement. A spasm is an involuntary contraction of muscle fibers.



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 wrinkles

Administration: subdermal injection Localized muscle paralysis occurs, so lines and wrinkles

are less apparent Effects lasts weeks to months Rarely covered by insurance



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 administered 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



Direct Acting Muscle Relaxants: Dantrolene (Dantrium)• 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



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



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



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


Other Muscle Disorders

Rhabdomyolysis • 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



Fibromyalgia• Is a chronic muscle pain condition that is not fully understood• 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 SNRIs



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 limbs• 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



Poliomyelitis (Polio)• Is a rare infection of nerves that control the muscular system• 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


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.


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


Summary• Muscle injury is the most common reason for using drug

therapy• Centrally acting muscle relaxants are used for muscle

injury• 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

2© paradigm publishing, inc. chapter 10 the muscular system and drug therapy

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