Opioid Analgesics & Pain Drug – Pharmacology
This chapter of Pharmacology covers Opioid analgesics and pain drug.
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
A patient who has metastasized bone cancer and therefore 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 long-term opioid.
c.an uncaring attitude toward the patient.
d. a failure to manage the patient’s pain properly.
Rationale: Patients with severe pain, including metastatic pain or bone pain, may need higher and higher doses of analgesics. The nurse is responsible for ensuring that the patient experiences adequate pain relief.
Opioid Analgesics:
Toxicity and Management of Overdose
-naloxone (Narcan)
-naltrexone (ReVia)
Regardless of withdrawal symptoms, when a patient experiences severe respiratory depression, an opioid antagonist should be given.
Toxicity and Management
of Overdose
-Opioid withdrawal/opioid abstinence syndrome
-Manifested as:
>Anxiety, irritability, chills and hot flashes, joint pain, lacrimation, rhinorrhea, diaphoresis, nausea, vomiting, abdominal cramps, diarrhea, and also confusion
Opioid Analgesics: Interactions
Alcohol
Antihistamines
Barbiturates
Benzodiazepines
Also Monoamine oxidase inhibitors
Nonopioid Analgesics:
Acetaminophen (Tylenol)
-Analgesic and antipyretic effects
-Little to no antiinflammatory effects
-Available over the counter and also in combination products with opioids
Acetaminophen: Mechanism of Action
-Similar to salicylates
-As a result blocks pain impulses peripherally by inhibiting prostaglandin synthesis
Acetaminophen: Indications
-Mild to moderate pain
-Fever
-Alternative for those who cannot take aspirin products
Acetaminophen: Dosage
-Maximum daily dose for healthy adults is being lowered to 3000 mg/day
>2000 mg for elderly or those with liver disease
-Inadvertent excessive doses may occur when different combination drug products are taken together
-Also be aware of the acetaminophen content of all medications taken by the patient (OTC and prescription)
Acetaminophen: Contraindications/Interactions
-Should not be taken in the presence of:
>Drug allergy
>Liver dysfunction
>Possible liver failure
>G6PD deficiency
-Dangerous interactions may occur if taken with alcohol or also other drugs that are hepatotoxic
Acetaminophen: Toxicity and Managing Overdose
-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
-Finally Recommended antidote: acetylcysteine regimen
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.1000 mg.
b.2000 mg.
c.3000 mg.
d.4000 mg.
Rationale: Chronic heavy alcohol abusers may be at increased risk of liver toxicity as a result of excessive acetaminophen use. For this reason, a maximum daily dose of 2000 mg is generally recommended for these persons.
Herbal Products: Feverfew
-Related to the marigold family
-Antiinflammatory properties
-Used to treat migraine headaches, menstrual cramps, inflammation, and also fever
-May cause GI distress, altered taste, therefore muscle stiffness
-May interact with aspirin and other NSAIDs, and also anticoagulants
Analgesics:
Nursing Implications
-Before beginning therapy, perform a thorough history regarding allergies and use of other medications, including alcohol, health history, and also medical history
-Obtain baseline vital signs and I&O
-Assess for potential contraindications and drug interactions
Analgesics: Nursing Implications
-Perform a thorough pain assessment, including pain intensity and character, onset, location, description, precipitating and relieving factors, type, remedies, and also other pain treatments
>Pain is now considered a “fifth vital sign”
>Rate pain on a 0 to 10 or similar scale
Analgesics:
Nursing Implications
-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 therefore be sure to include other interventions as indicated
Opioid Analgesics:
Nursing Implications
-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
Opioid Analgesics:
Nursing Implications
-Check dosages carefully
>Follow proper administration guidelines for IM injections, also including site rotation
>Follow proper guidelines for IV administration, including dilution, rate of administration, and so on
Opioid Analgesics:
Nursing Implications
-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 also to keep a record of their pain experience and response to treatments
-Patients should be instructed to change positions but slowly to prevent possible orthostatic hypotension
Opioid Analgesics:
Nursing Implications
-Monitor for adverse effects
>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
Opioid Analgesics:
Nursing Implications
-Monitor for therapeutic effects:
>Decreased complaints of pain
>Decreased severity of pain
>Increased periods of comfort
>Improved activities of daily living, appetite, and sense of well-being
>Also Decreased fever (acetaminophen)
Analgesics
Medications that relieve pain without causing loss of consciousness
“Painkillers”
Opioid analgesics- synthetic drugs that bind to opiate receptors to relieve pain
Adjuvant analgesic drugs- drugs that are added for combined therapy wit a primary drug and may have additive or independent analgesic properties, or both
Pain
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
Nociception
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
Tranducation
injured tissues releases chimicals that propagate pain message
Action potential moves along an afferent fiber to the spinal cord
transmission
the pain impulse moves from the spinal cord to the brain
perception of pain
in the brain
modulation
neurons from brain stem relaease neurotransmitters that block the pain impulse
pain threshold
Level of stimulus need to produce the perception of pain
A measure of the physiologic response of the nervous system
Pain Tolerance
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
Classification of Pain by Onset and Duration
Acute pain
Sudden onset
Usually subsides once treated
Chronic pain
Persistent or recurring
Lasts 3 to 6 months
Often difficult to treat
somatic
pain that originates from skeletal muscle, ligaments, or joints
visceral
pain that originates from organs or smooth muscles
superficial
pain that originates from the skin or mucous membranes
deep
pain that occurs in tissues below skin level; opposite of superficial
vascular
results from pathology of the vascular or perivascular tissue
reffered
pain occurring in an area away from the organ or origin
neuropathic
pain that result from a disturbance of function or pathologic change in a nerve
phantom
pain experienced in the area of a body part that has been surgically or traumatically removed
cancer
pain resulting from any disorder of causes related to cancer and/or metastasis
central
pain resulting from any disorder that causes CNS damage
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.Somatic pain
b.Referred pain
c.Visceral pain
d.Neuropathic pain*
Rationale: Somatic pain, which includes bone pain, originates from the skeletal muscles, ligaments, and joints. Referred pain occurs when visceral nerve fibers synapse at a level in the spinal cord close to fibers that supply specific subcutaneous tissues in the body. Visceral pain originates from organs and smooth muscles. Neuropathic pain usually results from damage to peripheral or CNS nerve fibers or injury but may also be idiopathic.
Gate Theory of Pain Transmission
-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
-gate control theory of pain asserts that non-painful input closes the “gates” to painful input, which prevents pain sensation from traveling to the central nervous system. Therefore, stimulation by non-noxious input is able to suppress pain.
Pain Transmission
Tissue injury causes the release of:
-Bradykinin
-Histamine
-Potassium
-Prostaglandins
-Serotonin
These substances stimulate nerve endings,
starting the pain process
Pain Transmission (cont’d)
-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
-Closing the gate stops the impulses
-If no impulses are transmitted to higher centers in the brain, there is no pain perception
Pain Transmission (cont’d)
-Body has endogenous neurotransmitters:
>Enkephalins
>Endorphins
-Produced by body to fight pain
-Bind to opioid receptors
-Inhibit transmission of pain by closing gate
Pain Transmission (cont’dd)
Rubbing a painful area with massage or liniment stimulates large sensory fibers
Result:
-Closes gate
-Reduces pain sensation
Treatment of Pain in Special Situations
-PCA and “PCA by proxy”
PCA by proxy = (activation by someone other than pt)
-Patient comfort vs. fear of drug addiction
-Opioid tolerance
-Use of placebos
-Recognizing patients who are opioid tolerant
-Breakthrough pain
-Synergistic effect
Adjuvant Drugs
-Assist primary drugs in relieving pain
>NSAIDs
>Antidepressants
>Anticonvulsants
>Corticosteroids
-Example: Adjuvant drugs for neuropathic pain
>amitriptyline (antidepressant)
>gabapentin or pregabalin (anticonvulsants)
Opioid Drugs
-Synthetic drugs that bind to the opiate receptors to relieve pain
-Very strong pain relievers
Opioid Ceiling Effect
-Drug reaches a maximum analgesic effect
-Analgesia does not improve, even with higher doses
>pentazocine
>nalbuphine
Opioid Analgesic 1
pentazocine
Opioid Analgesics 2
nalbuphine
Opioid Analgesics 3
codeine sulfate
Opioid Analgesics 4
meperidine HCl (Demerol)
Opioid Analgesics 5
methadone HCl (Dolophine)
Opioid Analgesics 6
morphine sulfate
Opioid Analgesics 7
Hydromorphone (Dilauded)
Opioid Analgesics 8
fentanyl (Duragesic)
Opioid Analgesics 9
oxycodone
Opioid Analgesics:
Mechanism of Action
Three classifications based on their actions:
>Agonist
>Partial agonist
>Antagonist
Agonists
-Bind to an opioid pain receptor in the brain
-Cause an analgesic response (reduction of pain sensation)
Agonists-Antagonists
-Bind to a pain receptor
-Cause a weaker neurologic response than a full agonist
-Also called partial agonist or mixed agonist
Antagonists
-Reverse the effects of these drugs on pain receptors
-Bind to a pain receptor and exert no response
-Also known as *competitive antagonists
Opioid Receptors and their charicteristics 1
-receptor type: mu
-prototypical agonist: morphine
-effects of opioid stimulation: supranasal analgesia, respiratory depression, euphoria, sedation(moderate level of sedation)
Opioid Receptors and their charicteristics 2
-receptor type: kappa
-prototypical agonist: keocyclazocine
-effects of opioid stimulation: spinal analgesia, sedation (twice as much sedation compared to mu receptors)
Opioid Receptors and their charicteristics 3
-receptor type: delta
-prototypical agonist: enkephalins
-effects of opioid stimulation: analgesia
Opioid Analgesics:
Indications
-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:
>Cough center suppression
>Treatment of diarrhea
>Balanced anesthesia
Opioid Analgesics:
Contraindications
-Known drug allergy
-Severe asthma
-Use with extreme caution in patients with:
>Respiratory insufficiency
>Elevated intracranial pressure
>Morbid obesity and/or sleep apnea
>Paralytic ileus
>Pregnancy
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.Pulse
b.Blood pressure
c.Temperature
d.Respirations (bc this drugs is a respitory despessant and pt has history of asthma)
Opioid Analgesics:
Adverse Effects
-CNS depression
>Leads to respiratory depression
>Most serious adverse effect
-Nausea and vomiting
-Urinary retention
-Diaphoresis and flushing
-Pupil constriction (miosis)
-Constipation
-Itching
Opioids: Opioid Tolerance
-A common physiologic result of chronic opioid treatment
-Result: larger dose is required to maintain the same level of analgesia
Opioids: Physical Dependence
-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)