opioid analgesics

Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved.
Opioid Analgesic AgentsOpioid Analgesic Agents

AnalgesicsAnalgesics
• Medications that relieve pain without causingMedications that relieve pain without causing
loss of consciousnessloss of consciousness
• PainkillersPainkillers

Classification of PainClassification of Pain
By Onset and DurationBy Onset and Duration
• Acute painAcute pain
– Sudden in onsetSudden in onset
– Usually subsides once treatedUsually subsides once treated
• Chronic painChronic pain
– Persistent or recurringPersistent or recurring
– Often difficult to treatOften difficult to treat

Classification of PainClassification of Pain
• SomaticSomatic
• VisceralVisceral
• SuperficialSuperficial
• VascularVascular
• ReferredReferred
• NeuropathicNeuropathic
• PhantomPhantom
• CancerCancer
• PsychogenicPsychogenic
• CentralCentral

Classification of Pain By SourceClassification of Pain By Source
Vascular painVascular pain
• Possibly originates from vascular orPossibly originates from vascular or
perivascular tissuesperivascular tissues
Neuropathic painNeuropathic pain
• Results from injury to peripheral nerve fibers orResults from injury to peripheral nerve fibers or
damage to the CNSdamage to the CNS
Superficial painSuperficial pain
• Originates from skin or mucous membranesOriginates from skin or mucous membranes

Pain Transmission Gate TheoryPain Transmission Gate Theory
• Most common and well-describedMost common and well-described
• Uses the analogy of a gate to describe howUses the analogy of a gate to describe how
impulses from damaged tissues are sensedimpulses from damaged tissues are sensed
in the brainin the brain

Pain TransmissionPain Transmission
Tissue injury causes the release of:Tissue injury causes the release of:
• BradykininBradykinin
• HistamineHistamine
• PotassiumPotassium
• ProstaglandinsProstaglandins
• SerotoninSerotonin
These substances stimulate nerve endings,These substances stimulate nerve endings,
starting the pain process.starting the pain process.

There are two types of nerves stimulated:There are two types of nerves stimulated:
• ““A” fibersA” fibers
andand
• ““C” fibersC” fibers

““A” FibersA” Fibers “C” Fibers“C” Fibers
Myelin sheathMyelin sheath No myelin sheathNo myelin sheath
Large fiber sizeLarge fiber size Small fiber sizeSmall fiber size
Conduct fastConduct fast Conduct slowlyConduct slowly
Inhibit painInhibit pain Facilitate painFacilitate pain
transmissiontransmission transmissiontransmission
Sharp andSharp and Dull andDull and
well-localizedwell-localized nonlocalizednonlocalized

• Types of pain related to proportion ofTypes of pain related to proportion of
“A” to “C” fibers in the damaged areas“A” to “C” fibers in the damaged areas

• These pain fibers enter the spinal cordThese pain fibers enter the spinal cord
and travel up to the brain.and travel up to the brain.
• The point of spinal cord entry is theThe point of spinal cord entry is the
DORSAL HORN.DORSAL HORN.
• The DORSAL HORN is the locationThe DORSAL HORN is the location
of the “GATE.”of the “GATE.”

• This gate regulates the flow of sensoryThis gate regulates the flow of sensory
impulses to the brain.impulses to the brain.
• Closing the gate stops the impulses.Closing the gate stops the impulses.
• If no impulses are transmitted to higherIf no impulses are transmitted to higher
centers in the brain, there is NO paincenters in the brain, there is NO pain
perception.perception.

Instructors may want to useInstructors may want to use
EIC Image #37:EIC Image #37:
Gate Theory of Pain TransmissionGate Theory of Pain Transmission

• Activation of large “A” fibers CLOSES gateActivation of large “A” fibers CLOSES gate
• Inhibits transmission to brainInhibits transmission to brain
– Limits perception of painLimits perception of pain

• Activation of small “B” fibers OPENS gateActivation of small “B” fibers OPENS gate
• Allows impulse transmission to brainAllows impulse transmission to brain
– Pain perceptionPain perception

• Gate innervated by nerve fibers from brain,Gate innervated by nerve fibers from brain,
allowing the brain some control over gateallowing the brain some control over gate
• Allows brain to:Allows brain to:
– Evaluate, identify, and localize the painEvaluate, identify, and localize the pain
– Control the gate before the gate is openControl the gate before the gate is open

““T” cellsT” cells
• Cells thatCells that controlcontrol the gate have a thresholdthe gate have a threshold
• Impulses must overcome threshold to be sentImpulses must overcome threshold to be sent
to the brainto the brain

• Body has endogenous neurotransmittersBody has endogenous neurotransmitters
– EnkephalinsEnkephalins
– EndorphinsEndorphins
• Produced by body to fight painProduced by body to fight pain
• Bind to opioid receptorsBind to opioid receptors
• Inhibit transmission of pain by closing gateInhibit transmission of pain by closing gate

Rubbing a painful area with massage orRubbing a painful area with massage or
liniment stimulates large sensory fibersliniment stimulates large sensory fibers
• Result:Result:
– GATE closed, recognition of pain REDUCEDGATE closed, recognition of pain REDUCED
– Same pathway used by opiatesSame pathway used by opiates

Opioid AnalgesicsOpioid Analgesics
• Pain relievers that contain opium,Pain relievers that contain opium,
derived from the opium poppyderived from the opium poppy
oror
• chemically related to opiumchemically related to opium
Narcotics: very strong pain relieversNarcotics: very strong pain relievers

• codeine sulfatecodeine sulfate
• meperidine HCl (Demerol)meperidine HCl (Demerol)
• methadone HCl (Dolophine)methadone HCl (Dolophine)
• morphine sulfatemorphine sulfate
• propoxyphene HClpropoxyphene HCl

Three classifications based on their actions:Three classifications based on their actions:
• AgonistAgonist
• Agonist-antagonistAgonist-antagonist
• Partial agonistPartial agonist

Opioid Analgesics: Site of actionOpioid Analgesics: Site of action
• Large “A” fibersLarge “A” fibers
• Dorsal horn of spinal cordDorsal horn of spinal cord

Opioid Analgesics:Opioid Analgesics:
Mechanism of ActionMechanism of Action
• Bind to receptors on inhibitory fibers,Bind to receptors on inhibitory fibers,
stimulating themstimulating them
• Prevent stimulation of the GATEPrevent stimulation of the GATE
• Prevent pain impulse transmissionPrevent pain impulse transmission
to the brainto the brain

Mechanism of ActionMechanism of Action
Three types of opioid receptors:Three types of opioid receptors:
• MuMu
• KappaKappa
• DeltaDelta

Opioid Analgesics: Therapeutic UsesOpioid Analgesics: Therapeutic Uses
Main use: to alleviate moderate to severe painMain use: to alleviate moderate to severe pain
• Opioids are also used for:Opioids are also used for:
– Cough center suppressionCough center suppression
– Treatment of constipationTreatment of constipation

Opioid Analgesics: Side EffectsOpioid Analgesics: Side Effects
• EuphoriaEuphoria
• Nausea and vomitingNausea and vomiting
• Respiratory depressionRespiratory depression
• Urinary retentionUrinary retention
• Diaphoresis and flushingDiaphoresis and flushing
• Pupil constriction (miosis)Pupil constriction (miosis)
• ConstipationConstipation

Opiate AntagonistsOpiate Antagonists
naloxone (Narcan)naloxone (Narcan)
naltrexone (Revia)naltrexone (Revia)
• Opiate antagonistsOpiate antagonists
• Bind to opiate receptors and prevent a responseBind to opiate receptors and prevent a response
Used for complete or partial reversal ofUsed for complete or partial reversal of
opioid-induced respiratory depressionopioid-induced respiratory depression

Opiates: Opioid ToleranceOpiates: Opioid Tolerance
• A common physiologic result of chronicA common physiologic result of chronic
opioid treatmentopioid treatment
• Result:Result: larger dose of opioids are requiredlarger dose of opioids are required
to maintain the same level ofto maintain the same level of
analgesiaanalgesia

Opiates: Physical DependenceOpiates: Physical Dependence
• The physiologic adaptation of the body toThe physiologic adaptation of the body to
the presence of an opioidthe presence of an opioid

Opiates: Psychological DependenceOpiates: Psychological Dependence
(addiction)(addiction)
• A pattern of compulsive drug useA pattern of compulsive drug use
characterized by a continued craving forcharacterized by a continued craving for
an opioid and the need to use the opioidan opioid and the need to use the opioid
for effects other than pain relieffor effects other than pain relief

OpiatesOpiates
• Opioid tolerance and physical dependenceOpioid tolerance and physical dependence
are expected with long-term opioid treatmentare expected with long-term opioid treatment
and should not be confused withand should not be confused with
psychological dependence (addiction).psychological dependence (addiction).

OpiatesOpiates
• Misunderstanding of these terms leads toMisunderstanding of these terms leads to
ineffective pain management and contributesineffective pain management and contributes
to the problem of undertreatment.to the problem of undertreatment.

OpiatesOpiates
• Physical dependence on opioids is seenPhysical dependence on opioids is seen
when the opioid is abruptly discontinued orwhen the opioid is abruptly discontinued or
when an opioid antagonist is administered.when an opioid antagonist is administered.
– Narcotic withdrawalNarcotic withdrawal
– Opioid abstinence syndromeOpioid abstinence syndrome

OpiatesOpiates
Narcotic Withdrawal Opioid AbstinenceNarcotic Withdrawal Opioid Abstinence
SyndromeSyndrome
• Manifested as:Manifested as:
– anxiety, irritability, chills and hot flashes, jointanxiety, irritability, chills and hot flashes, joint
pain, lacrimation, rhinorrhea, diaphoresis,pain, lacrimation, rhinorrhea, diaphoresis,
nausea, vomiting, abdominal cramps, diarrheanausea, vomiting, abdominal cramps, diarrhea

Nursing ImplicationsNursing Implications
• Before beginning therapy, perform aBefore beginning therapy, perform a
thorough history regarding allergies, use ofthorough history regarding allergies, use of
other medications,health history, andother medications,health history, and
medical history.medical history.
• Obtain baseline vital signs and I & O.Obtain baseline vital signs and I & O.
• Assess for potential contraindications andAssess for potential contraindications and
drug interactions.drug interactions.

• Perform a thorough pain assessment,Perform a thorough pain assessment,
including nature and type of pain,including nature and type of pain,
precipitating and relieving factors, remedies,precipitating and relieving factors, remedies,
and other pain treatments.and other pain treatments.
– Assessment of pain is now being consideredAssessment of pain is now being considered
a “fifth vital sign.”a “fifth vital sign.”

• Be sure to medicate patients before the painBe sure to medicate patients before the pain
becomes severe as to provide adequatebecomes severe as to provide adequate
analgesia and pain control.analgesia and pain control.
• Pain management includes pharmacologicPain management includes pharmacologic
and nonpharmacologic approaches. Be sureand nonpharmacologic approaches. Be sure
to include other interventions as indicated.to include other interventions as indicated.

• Oral forms should be taken with food toOral forms should be taken with food to
minimize gastric upset.minimize gastric upset.
• Ensure safety measures, such as keepingEnsure safety measures, such as keeping
side rails up, to prevent injury.side rails up, to prevent injury.
• Withhold dose and contact physician if thereWithhold dose and contact physician if there
is a decline in the patient’s condition or if VSis a decline in the patient’s condition or if VS
are abnormal—especially if respiratory rateare abnormal—especially if respiratory rate
is below 12 breaths/minute.is below 12 breaths/minute.

• Follow proper administration guidelines forFollow proper administration guidelines for
IM injections, including site rotation.IM injections, including site rotation.
• Follow proper guidelines for IVFollow proper guidelines for IV
administration, including dilution, rate ofadministration, including dilution, rate of
administration, and so forth.administration, and so forth.
CHECK DOSAGES CAREFULLYCHECK DOSAGES CAREFULLY

• Constipation is a common side effect andConstipation is a common side effect and
may be prevented with adequate fluid andmay be prevented with adequate fluid and
fiber intake.fiber intake.
• Instruct patients to follow directions forInstruct patients to follow directions for
administration carefully, and to keep aadministration carefully, and to keep a
record of their pain experience andrecord of their pain experience and
response to treatments.response to treatments.
• Patients should be instructed to changePatients should be instructed to change
positions slowly to prevent possiblepositions slowly to prevent possible
orthostatic hypotension.orthostatic hypotension.

• Patients should not take other medicationsPatients should not take other medications
or OTC preparations without checking withor OTC preparations without checking with
their physician.their physician.
• Instruct patients to notify physician for signsInstruct patients to notify physician for signs
of allergic reaction or adverse effects.of allergic reaction or adverse effects.

Monitor for side effects:Monitor for side effects:
• Should VS change, patient’s condition decline,Should VS change, patient’s condition decline,
or pain continue, contact physician immediately.or pain continue, contact physician immediately.
• Respiratory depression may be manifested byRespiratory depression may be manifested by
respiratory rate of less than 12/min, dyspnea,respiratory rate of less than 12/min, dyspnea,
diminished breath sounds, or shallow breathing.diminished breath sounds, or shallow breathing.

Monitor for therapeutic effects:Monitor for therapeutic effects:
• Decreased complaints of painDecreased complaints of pain
• Increased periods of comfortIncreased periods of comfort
• With improved activities of daily living, appetite,With improved activities of daily living, appetite,
and sense of well-beingand sense of well-being

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