Analgesic Drugs (Chapter 10)
Recording: (14 minutes)
https://fiu.zoom.us/rec/share/dSUoO5sqMWVsSZY4prt6K2aCRAgIdQ32hP7cT_Nk_fL1OTLztN59aYLEo1edOy2.Nj3r42IgiJmdfM8d
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Nociceptors
o Pain results from stimulation of sensory nerve fibers called nociceptors
o These receptors transmit pain signals from various body regions to the spinal cord and brain
Acute pain
o Sudden onset
o Usually subsides once treated
Chronic pain
o Persistent or recurring
o Lasts 3 to 6 months
o Often difficult to treat
o Tolerance
o Physical dependence
Classification of Pain
o Somatic - bone pain, originates from the skeletal muscles, ligaments, and joints
o Visceral - originates from organs and smooth muscles
o Superficial
o Deep
o Vascular
o Referred - visceral nerve fibers synapse at a level in the spinal cord close to fibers that
supply specific subcutaneous tissues in the body
o Neuropathic - usually results from damage to peripheral or CNS nerve fibers or injury, but
may also be idiopathic
o Phantom
o Cancer
o Central
Pain Transmission
o Tissue injury causes the release of the following:
 Bradykinin
 Histamine
 Potassium
 Prostaglandins
 Serotonin
o These substances stimulate nerve endings, starting the pain process.
o Nerve → spinal cord (dorsal horn = “gate”) → brain
o Endogenous neurotransmitters produced by body to fight pain by binding to opioid
receptors and “closing gate”
 Enkephalins
 Endorphins
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Step 1: nonopiods +/- adjuvant drugs
Step 2: opioids +/- nonopiods +/- adjuvant drugs
Step 3: +/- all of the above
Teaching:
o Pain is the “fifth vital sign”
o Take with food to minimize gastric upset
o Contact provider if respiratory rate is less than 10-12 breaths/min
Adjuvant Drugs
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Assist primary drugs in relieving pain
o NSAIDs
o Antidepressants
 Amitriptyline (antidepressant)
o Anticonvulsants
 Gabapentin or pregabalin (anticonvulsants)
o Corticosteroids
Opioid Drugs
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Indications:
o Moderate to severe pain
o Cough center suppression
o Treatment of diarrhea
o Balanced anesthesia
CI: severe asthma
Caution: Respiratory insufficiency, Elevated intracranial pressure, Morbid obesity or sleep apnea,
Paralytic ileus, Pregnancy
AE: CNS depression, n/v, urinary retention, diaphoresis, flushing, miosis, constipation, itching, opioid
tolerance, physical dependence
Interactions: alcohol, antihistamines, barbiturates, benzodiazepines, MAOIs
Management of overdose:
o Naloxone (Narcan)
 Pure opioid antagonist
 Drug of choice for the complete or partial reversal of opioid-induced respiratory
depression
 Indicated in cases of suspected acute opioid overdose
 Failure of the drug to significantly reverse the effects of the presumed opioid
overdose indicates that the condition may not be related to opioid overdose.
 Naloxone now available without a prescription and is being used by 1st responders
for opioid/illegal drug overdoses
o Naltrexone (ReVia)
 Opioid antagonist
 Oral form
 Used for alcohol and opioid addiction
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Regardless of withdrawal symptoms, when a patient experiences severe respiratory
depression, an opioid antagonist should be given
Opioid withdrawal or opioid abstinence syndrome:
o Anxiety, irritability, chills and hot flashes, joint pain, lacrimation, rhinorrhea, diaphoresis,
nausea, vomiting, abdominal cramps, diarrhea, confusion
Mild agonists:
o codeine, hydrocodone
Strong agonists:
o morphine, hydromorphone, oxycodone, meperidine*, fentanyl, and methadone
o Meperidine: not recommended for long-term use because of the accumulation of a
neurotoxic metabolite, normeperidine, which can cause seizures
Three classifications based on their actions
o Agonists
 Bind to an opioid pain receptor in the brain and reduce pain sensation
o Agonists-antagonists
 Bind to pain receptor cause a weaker neurologic response than a full agonists
 Also called partial agonists or mixed agonist
o Antagonists (nonanalgesic)
 Bind to a pain receptor and exert no response
 Also known as competitive antagonists
 Reverse the effects of these drugs on pain receptors
 For example:
 Narcan
 ReVita
Ceiling effect
 Drug reaches max analgesic effect, even with higher doses
Equianalgesia:
o Ability to provide equivalent pain relief by calculating dosages of different drugs or routes of
administration that provide comparable analgesia
Opioid Agonists: Schedule II
o Codeine Sulfate
o Fentanyl
o Hydromorphone (Dilaudid)
o Meperidine
o Methadone Hydrochloride (Dolophine)
o Morphine Sulfate
o Oxycodone hydrochloride
Opioid Agonists-Antagonists: Schedule IV
o Buprenorphine (Buprenex)
o Butorphanol (Stadol)
o Nalbuphine (Nubain)
o Pentazocine (Talwin)
Opioid Antagonists:
o Narcan
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o ReVita
Nonopioid Analgestics:
o Acetaminophen (Tylenol)
 Analgesic, antipyretic, no anti-inflammatory effects
 MOA: similar to salicylates, blocks pain impulses peripherally by inhibiting
prostaglandin synthesis
 Max dose: 3000 mg/day
 2000 mg/day for older adults and those with liver dz
 CI: drug allergy, liver dysfunction, possible liver failure, G6PD deficiency
 Recommended antidote: acetylcysteine regimen
o Tramadol Hydrochloride (Ultram)
 Centrally acting analgesic with a dual mechanism of action
 Weak bond to mu opioid receptors
 Inhibits the reuptake of norepinephrine and serotonin
 Not classified as a controlled substance (CIV)
 Indicated for moderate to moderately severe pain
 Adverse effects similar to those of opioids
 Careful use in patients taking SSRIs, MAOIs, neuroleptics
Lidocaine, transdermal
o Topical anesthetic
o Indications: postherpetic neuralgia
o Left in place no longer than 12 hours
o Minimal adverse effects
o Skin irritation may occur
Herbal Products: Feverfew
o Related to the marigold family
o Antiinflammatory properties
o Used to treat migraine headaches, menstrual cramps, inflammation, and fever
o May cause GI distress, altered taste, muscle stiffness
o May interact with aspirin and other NSAIDs, as well as anticoagulants