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Summary NUR 243 Opioid & CNS Agents

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This is a comprehensive and detailed summary on Opioid & CNS Agents from the book Pharmacology for Nursing Care by Richard A. Lehne *Essential Study Material!!

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  • September 18, 2024
  • 34
  • 2019/2020
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OPIOID ANALGESICS, OPIOID ANTAGONISTS, AND NONOPIOID CENTRALLY ACTING
ANALGESICS
Terms:
1. Analgesic→ drug that relieves pain w/o causing loss of consciousness
2. Opioid→ any drug, natural or synthetic, that has actions similar to morphine
3. Opiate→ more specific; applies only to compounds present in opium (morphine,
codeine)
Review:
Partial agonist→ drug that produces low to moderate receptor activation when
administered alone but will block the actions of a full agonist drug when paired
together (agonistic and antagonistic)
-Endogenous Opioid Peptides (3)
-enkephalins, endorphins, dynorphins
-opioid like properties
-found in CNS and peripheral nervous tissue
-act through all opioid receptors: mu, kappa, and delta receptors
Opioid Receptors:

a. Most important→ opioid analgesics act primarily by activating mu
receptors
b. r/t physical dependence
c. Responses
i. Analgesia
ii. Respiratory depression
iii. Sedation
iv. Decreased GI motility
v. Euphoria

a. Weak activation by opioid analgesics
b. Possibly underlying psychotomimetic effects
c. Responses
i. Analgesia
ii. Some respiratory depression
iii. Sedation
iv. Decreased GI motility

a. Opioid analgesics do not interact
*opioid analgesics→ act through mu and kappa receptors
*endogenous opioid peptides→ act through all three receptors (including delta)

,Drugs That Act At Opioid Receptors:
1. Pure Opioid Agonists
a. Activate mu and kappa receptors
b. Produce analgesia, euphoria, sedation, respiratory depression, physical
dependence, constipation
c. Two types:
i. Strong opioid agonists
1. MORPHINE
ii. Moderate to strong opioid agonists
1. CODEINE
2. Agonist-Antagonist Opioids
a. 4 available (pentazocine, nalbuphine, buprenorphine, butorphanol)
b. Activate mu and kappa receptors
c. When administered alone→ ANALGESIA
d. When administered w/ pure opioid agonist→ ANTAGONIZE ANALGESIA
e. prototype→ Pentazocine (talwin)
3. Pure Opioid Antagonists
a. Act as antagonists at mu and kappa receptors
b. Do not produce effects of opioids
c. Clinical use→ reversal of respiratory and CNS depression caused by
overdose of opioid agonist
d. methylnaltrexone→ reverses opioid induced constipation
e. prototype→ Naloxone (narcan)

Prototype for strong opioid analgesic
● Mimics actions of endogenous opioid peptides, primarily at mu receptors
● Principle indication→ relief of moderate to severe pain
● Relieves pain w/o affecting other senses/ causing loss of consciousness
● More effective against dull, constant pain than against sharp, intermittent
pain; sharp pain can be relieved by higher doses
● Indicated for postop pain, preop sedation and anxiety, labor/delivery pain,
chronic pain caused by cancer
● Not first line for pain of MI, pain of dyspnea assoc. w/ left ventricular failure
and pulmonary edema
● Pharmacological effects→
○ analgesia, sedation, euphoria, drowsiness, mental clouding, reduced
anxiety, increased sense of well-being
● Pharmacological Effects Due to Actions at the CNS and Periphery
○ Respiratory suppression

, ○ Bowel motility suppression→ constipation
○ Cough suppression
○ Urinary retention
○ Orthostatic hypotension
○ Biliary colic
■ Gallstone attack
○ Emesis
○ Miosis
■ Contraction of the pupil
● Opioid peptides and morphine like drugs affect regions of the brain and spinal
cord associated with perception of pain
● Tolerance and physical dependence can occur with prolonged use
CROSS TOLERANCE→
● Subjects rendered tolerant to analgesia form morphine-like drugs show
cross-tolerance to analgesia from opioid peptides
● The analgesia effects of opioid peptides and morphine-like drugs can both be
blocked by the same antagonist→ naloxone
ADVERSE EFFECTS→
● 
○ MOST SERIOUS ADVERSE EFFECT
○ Death from overdose almost always from resp. depression
○ Through activation of mu receptors; kappa receptors also contribute
○ Time of respiratory depression correlates with route of
administration→
○ IV Onset: 7 minutes
○ IM Onset: 30 minutes
○ SubQ Onset: 90 minutes
○ Spinal injection Onset: 
○ Duration of all respiratory depression: 4-5 hours
○ Prolonged use/long term opioid use→ tolerance to resp. depression
○ When administered at therapeutic doses, opioids rarely cause
significant respiratory depression
○ Increased by concurrent use of drugs with CNS-depressant actions:
AVOID→
■ Alcohol, Barbiturates, and Benzodiazepines

○ RR should be determined before opioid administration
○ w/hold med if RR <12

, ○ caution/close monitoring in very young pts, older adults, pts w asthma,
and emphysema→ these pts are more prone to respiratory
suppression
○ REVERSAL→ naloxone (narcan); opioid antagonist

○ Through actions in CNS and GI tract
○ Activation of mu receptors in the gut
○ Drugs suppress propulsive intestinal contractions, intensify non
propulsive contractions, increase the tone of the anal sphincter, and
inhibit secretion of fluids into the intestinal lumen
○ Opioids are highly effective for treating Diarrhea
○ Other occurrences→
○ Fecal impaction, bowel perforation, rectal tearing, hemorrhoids
○ TREATMENT:
■ Physical activity and increase fiber and fluid intake
■ Enemas
■ Prophylactic drug use→ laxatives
● Stimulant laxative
● Senna→ counteract reduced bowel motility
● Docusate (colace) → stool softener
● Polyethylene glycol→ osmotic laxative 
■ Prophylactic drugs inadequate→ Rescue Therapy with a strong
osmotic laxative
● Lactulose
● Sodium phosphate
■ No response w/ enema or laxatives→ methylnaltrexone (relistor)
● Oral drug
● Blocks mu receptors at intestine
● Can’t cross BBB→ can’t reverse opioid induced analgesia

○ Blunting of the baroreceptor reflex and peripheral dilation: peripheral
arterioles and veins (results from morphine-induced histamine)
○ 
○ hypotensive drugs can exacerbate opioid-induced hypotension
● 
○ Increases tone in bladder, bladder sphincter, and detrusor muscle,
○ Elavates bladder pressure→ sense of urinary urgency
○ Suppression of awareness to bladder stimuli

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