Chapter 10
Analgesic Drugs
Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Analgesics
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Medications that relieve pain without causing loss of
consciousness
“Painkillers”
Opioid analgesics
Adjuvant analgesic drugs
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Pain
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An unpleasant sensory and emotional experience
associated with actual or potential tissue damage
A personal and individual experience
Whatever the patient says it is
Exists when the patient says it exists
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Nociception
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Pain results from stimulation of sensory nerve
fibers called nociceptors
These receptors transmit pain signals from
various body regions to the spinal cord and brain
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Nociception (cont’d)
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Pain Threshold
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Level of stimulus needed to produce the
perception of pain
A measure of the physiologic response of the
nervous system
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Pain Tolerance
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The amount of pain a person can endure without it
interfering with normal function
Varies from person to person
Subjective response to pain, not a physiologic function
Varies by attitude, environment, culture, ethnicity
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Classification of Pain
by Onset and Duration
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Acute pain
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Sudden onset
Usually subsides once treated
Chronic pain
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Persistent or recurring
Lasts 3 to 6 months
Often difficult to treat
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Classification of Pain
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Somatic
Visceral
Superficial
Deep
Vascular
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Referred
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Neuropathic
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Phantom
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Cancer
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Central
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Classroom Response Question
A patient with bone cancer tells the nurse that he is in pain.
The nurse knows that bone pain is classified as which type
of pain?
A.
B.
C.
D.
Somatic pain
Referred pain
Visceral pain
Neuropathic pain
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Gate Theory of Pain Transmission
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Most common and well-described theory
Uses the analogy of a gate to describe how impulses
from damaged tissues are sensed in the brain
Many current pain management strategies are aimed at
altering this system
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Gate Theory of Pain
Transmission (cont’d)
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Pain Transmission
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Tissue injury causes the release of:
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Bradykinin
Histamine
Potassium
Prostaglandins
Serotonin
These substances stimulate nerve endings,
starting the pain process
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Pain Transmission (cont’d)
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The nerve impulses enter the spinal cord
and travel up to the brain
The point of spinal cord entry or the “gate” is the
dorsal horn
This gate regulates the flow of sensory impulses
to the brain
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Pain Transmission (cont’d)
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Closing the gate stops the impulses
If no impulses are transmitted to higher centers
in the brain, there is no pain perception
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Pain Transmission (cont’d)
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Body has endogenous neurotransmitters
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Enkephalins
Endorphins
Produced by body to fight pain
Bind to opioid receptors
Inhibit transmission of pain by closing gate
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Pain Transmission (cont’d)
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Rubbing a painful area with massage or liniment
stimulates large sensory fibers
Result
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Closes gate
Reduces pain sensation
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Treatment of Pain in Special
Situations
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PCA and “PCA by proxy”
Patient comfort vs. fear of drug addiction
Opioid tolerance
Use of placebos
Recognizing patients who are opioid tolerant
Breakthrough pain
Synergistic effect
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Adjuvant Drugs
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Assist primary drugs in relieving pain
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NSAIDs
Antidepressants
Anticonvulsants
Corticosteroids
Example: Adjuvant drugs for neuropathic pain
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amitriptyline (antidepressant)
 gabapentin or pregabalin (anticonvulsants)
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Opioid Drugs
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Synthetic drugs that bind to the opiate receptors
to relieve pain
Very strong pain relievers
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Opioid Ceiling Effect
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Drug reaches a maximum analgesic effect
Analgesia does not improve, even with higher
doses
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pentazocine
nalbuphine
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Opioid Analgesics (cont’d)
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codeine sulfate
meperidine HCl (Demerol)
methadone HCl (Dolophine)
morphine sulfate
hydromorphone
fentanyl (Duragesic)
oxycodone
Others
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Opioid Analgesics:
Mechanism of Action
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Three classifications based on their actions:
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Agonist
Partial agonist
Antagonist
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Agonists
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Bind to an opioid pain receptor in the brain
Cause an analgesic response (reduction of pain
sensation)
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Agonists-Antagonists
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Bind to a pain receptor
Cause a weaker neurologic response than a full
agonist
Also called partial agonist or mixed agonist
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Antagonists
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Reverse the effects of these drugs on pain
receptors
Bind to a pain receptor and exert no response
Also known as competitive antagonists
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Opioid Analgesics:
Indications
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Main use: to alleviate moderate to severe pain
Often given with adjuvant analgesic drugs to
assist primary drugs with pain relief
Opioids are also used for:
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Cough center suppression
Treatment of diarrhea
Balanced anesthesia
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Opioid Analgesics:
Contraindications
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Known drug allergy
Severe asthma
Use with extreme caution in patients with:
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Respiratory insufficiency
Elevated intracranial pressure
Morbid obesity and/or sleep apnea
Paralytic ileus
Pregnancy
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Classroom Response Question
A patient is recovering from an appendectomy. She also
has asthma and allergies to shellfish and iodine. To
manage her postoperative pain, the physician has
prescribed patient-controlled analgesia (PCA) with
hydromorphone (Dilaudid). Which vital sign is of greatest
concern?
A.
B.
C.
D.
Pulse
Blood pressure
Temperature
Respirations
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Opioid Analgesics:
Adverse Effects
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CNS depression
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Leads to respiratory depression
Most serious adverse effect
Nausea and vomiting
Urinary retention
Diaphoresis and flushing
Pupil constriction (miosis)
Constipation
Itching
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Opioids: Opioid Tolerance
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A common physiologic result of chronic opioid
treatment
Result: larger dose is required to maintain the
same level of analgesia
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Opioids: Physical Dependence
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Physiologic adaptation of the body to the
presence of an opioid
Opioid tolerance and physical dependence are
expected with long-term opioid treatment and
should not be confused with psychologic
dependence (addiction)
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Opioids: Psychologic Dependence

A pattern of compulsive drug use characterized
by a continued craving for an opioid and the
need to use the opioid for effects other than pain
relief
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Classroom Response Question
A patient who has metastasized bone cancer has been on
transdermal fentanyl patches for pain management for 3 months.
He has been hospitalized for tests and has told the nurse that his
pain is becoming “unbearable.” The nurse is reluctant to give him
the ordered pain medication because the nurse does not want
the patient to get addicted to the medication. The nurse’s actions
reflect
A. appropriate concern for the patient’s best welfare.
B. appropriate caution for a patient who is already on a longterm opioid.
C. an uncaring attitude toward the patient.
D. a failure to manage the patient’s pain properly.
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Opioid Analgesics:
Toxicity and Management of
Overdose
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naloxone (Narcan)
naltrexone (ReVia)
Regardless of withdrawal symptoms, when a patient
experiences severe respiratory depression, an opioid
antagonist should be given.
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Toxicity and Management
of Overdose (cont’d)
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Opioid withdrawal/opioid abstinence syndrome
Manifested as:
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Anxiety, irritability, chills and hot flashes, joint pain,
lacrimation, rhinorrhea, diaphoresis, nausea,
vomiting, abdominal cramps, diarrhea, confusion
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Opioid Analgesics: Interactions
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Alcohol
Antihistamines
Barbiturates
Benzodiazepines
Monoamine oxidase inhibitors
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Nonopioid Analgesics:
Acetaminophen (Tylenol)
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Analgesic and antipyretic effects
Little to no antiinflammatory effects
Available over the counter and in combination
products with opioids
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Acetaminophen: Mechanism of
Action
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Similar to salicylates
Blocks pain impulses peripherally by inhibiting
prostaglandin synthesis
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Acetaminophen: Indications
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Mild to moderate pain
Fever
Alternative for those who cannot take aspirin
products
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Acetaminophen: Dosage
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Maximum daily dose for healthy adults is being lowered
to 3000 mg/day
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2000 mg for elderly or those with liver disease
Inadvertent excessive doses may occur when different
combination drug products are taken together
Be aware of the acetaminophen content of all
medications taken by the patient (OTC and prescription)
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Acetaminophen:
Contraindications/Interactions
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Should not be taken in the presence of
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Drug allergy
Liver dysfunction
Possible liver failure
G6PD deficiency
Dangerous interactions may occur if taken with alcohol
or other drugs that are hepatotoxic
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Acetaminophen: Toxicity and
Managing Overdose
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Even though available over the counter, lethal when
overdosed
Overdose, whether intentional or resulting from chronic
unintentional misuse, causes hepatic necrosis:
hepatotoxicity
Long-term ingestion of large doses also causes
nephropathy
Recommended antidote: acetylcysteine regimen
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Classroom Response Question
A patient with a history of heavy alcohol use needs a
medication for pain. The recommended maximum daily
dose of acetaminophen for this patient would be
A.
B.
C.
D.
1000 mg.
2000 mg.
3000 mg.
4000 mg.
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Herbal Products: Feverfew
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Related to the marigold family
Antiinflammatory properties
Used to treat migraine headaches, menstrual cramps,
inflammation, and fever
May cause GI distress, altered taste, muscle stiffness
May interact with aspirin and other NSAIDs, and
anticoagulants
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Analgesics:
Nursing Implications
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Before beginning therapy, perform a thorough history
regarding allergies and use of other medications,
including alcohol, health history, and medical history
Obtain baseline vital signs and I&O
Assess for potential contraindications and drug
interactions
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Analgesics:
Nursing Implications (cont’d)
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Perform a thorough pain assessment, including pain
intensity and character, onset, location, description,
precipitating and relieving factors, type, remedies, and
other pain treatments
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Pain is now considered a “fifth vital sign”
Rate pain on a 0 to 10 or similar scale
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Analgesics:
Nursing Implications (cont’d)
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Be sure to medicate patients before the pain becomes
severe so as to provide adequate analgesia and pain
control
Pain management includes pharmacologic and
nonpharmacologic approaches; be sure to include other
interventions as indicated
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Analgesics:
Nursing Implications (cont’d)
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Patients should not take other medications or OTC
preparations without checking with their physician
Instruct patients to notify physician for signs of allergic
reaction or adverse effects
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Opioid Analgesics:
Nursing Implications
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Oral forms should be taken with food to minimize gastric
upset
Ensure safety measures, such as keeping side rails up,
to prevent injury
Withhold dose and contact physician if there is a decline
in the patient’s condition or if vital signs are abnormal,
especially if respiratory rate is less than 10 to 12
breaths/min
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Opioid Analgesics:
Nursing Implications (cont’d)
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Check dosages carefully
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Follow proper administration guidelines for IM
injections, including site rotation
Follow proper guidelines for IV administration,
including dilution, rate of administration, and so on
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Opioid Analgesics:
Nursing Implications (cont’d)
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Constipation is a common adverse effect and
may be prevented with adequate fluid and
fiber intake
Instruct patients to follow directions for administration
carefully and to keep a record of their pain experience
and response to treatments
Patients should be instructed to change positions slowly
to prevent possible orthostatic hypotension
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Opioid Analgesics:
Nursing Implications (cont’d)
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Monitor for adverse effects
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Contact physician immediately if vital signs change,
patient’s condition declines, or pain continues
Respiratory depression may be manifested by
respiratory rate of less than 10 breaths/min, dyspnea,
diminished breath sounds, or shallow breathing
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Opioid Analgesics:
Nursing Implications (cont’d)
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Monitor for therapeutic effects
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Decreased complaints of pain
Decreased severity of pain
Increased periods of comfort
Improved activities of daily living, appetite, and sense
of well-being
Decreased fever (acetaminophen)
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