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PHRX 3009: drug action > 40. Drug Action on Opioid Receptors > Flashcards

40. Drug Action on Opioid Receptors Flashcards

1
Q

Explain the categories of opioid receptors based on potency.

A

Stong agonists
* Morphine
* Hydromorphone
* Oxymorphone
* Methadone
* Meperidine
* Fentanyl
* Levorphanol

Mild to moderate
* Codeine
* Oxycodone
* Dihyrocodeine
* Hydrocodone
* Propoxyphene
* Diphenoxylate
* Loperamide

Mixed agonists and antagonists
* Nalbuphine
* Buprenorphine
* Butorphanol
* Pentazocine
* Dezocine

Antagonists
* Naloxone
* Naltrexone
* Nalmefene

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2
Q

Describe the basic characteristics of morphine.

A

Strong agonist of opioid receptors
* found naturally in plants and animals
* a benzylisoquinoline alkaloid with two additional ring closures
* morphine sulfate injection - 50 mg/mL
* morphine sulfate tablet - 60 mg/mL

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3
Q

Explain how morphine acts in the body.

A
  • binds to and activates the u-opioid receptor (STRONG AGONIST) in the CNS and GI –> results in analgesia, sedation, euphoria, physical dependence, and respiratory depression
  • binds to and activates the k-opioid receptor to associate with spinal analgesia, miosis (pinpoint pupils), and psychotomimetic effects
  • doesn’t directly bind to the d-opioid receptor, but is involved in downstream functions of the d-opioid receptor
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4
Q

What are the effects of morphine?

A
  • analgesia
  • euphoria
  • respiratory depression
  • antitussive
  • miosis
  • slow GI tract
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5
Q

Describe the association between morphine and analgesia.

A

Morphine causes analgesia by:
* raising pain threshold at the spinal cord level
* altering the brain’s perception of pain

Patients treated with morphine are aware of the presence of pain, but the sensation is not unpleasant

analgesia - relief of pain without the loss of consciousness

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6
Q

Describe the association between morphine and euphoria.

A

Euphoria is caused by disinhibition of the dopamine-containing neurons of the ventral tegmental area.
* powerful sense of contentment and well-being.

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7
Q

Describe the association between morphine and respiratory depression.

A

Morphine causes respiratory depression by reduction of the sensitivity of respiratory center neurons to CO2.
* most common cause of death in acute opioid overdoses
* tolerance to respiratory depression develops quickly with repeated dosing –> allows safe use of morphine for treatment of pain

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8
Q

Describe the association between morphine and cough.

A

Morphine has antitussive properties
* the receptors involved in the antitussive action are different from those involved in analgesia (inability to feel pain)

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9
Q

Describe the association between morphine and miosis (pinpoint pupils).

A

Morphine causes miosis because of stimulation of u and k receptors.
* little tolerance to miosis –> all morphine abusers have pinpoint pupils
* Important for diagnosis because many other causes of coma and respiratory depresssion produce dilation of the pupil

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10
Q

Describe the association between morphine and emesis.

A

Morphine causes emesis (vomiting) because it directly stimulates the chemoreceptor trigger zone in the area postrema.

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11
Q

Describe the association between morphine and diarrhea/constipation.

A

Morphine relieves diarrhea by decreasing the motility and increasing the tone of the intestinal circular smooth muscle.
* produces constipation with little tolerance developing
* stool softener docusate + stimulant laxative senna = treats opioid-induced constipation.

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12
Q

Describe the association between morphine and diarrhea/constipation.

A

Morphine relieves diarrhea by decreasing the motility and increasing the tone of the intestinal circular smooth muscle.
* produces constipation with little tolerance developing
* stool softener docusate + stimulant laxative senna = treats opioid-induced constipation.

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13
Q

Describe the association between morphine and the biliary tract.

A

Morphine can increase biliary tract pressure due to contraction of the gallbladder and constiction of the biliary spincter.

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14
Q

Describe the association between morphine and the cardiovascular system.

A

At low doses, there are no major effects on blood pressure or heart rate.
At high doses, hypotension and bradycardia may occur.

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15
Q

Describe the association between morphine and histamine.

A

Morphine releases histamine from mast cells causing urticaria, sweating, and vasodilation.
* should be used with caution in patients with asthma because it can cause bronchoconstriction

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16
Q

What are the medical uses of morphine?

A
  • pain relief
  • acute pulmonary edema
  • shortness of breath.
  • opioid use disorder
17
Q

Explain tolerance and physical dependence of morphine.

A

Repeated use of morphine produces tolerance to the respiratory depressant, analgesic, euphoric, and sedative effects of morphine.
* tolerence doesn’t develop for miosis

Physical and psychological dependence can occur with morphine

Withdrawal - produces a series of autonomic, motor, and psychological responses that incapacitate the individual and causes serious symptoms (death is rare)

18
Q

Describe the characteristics of hydromorphone.

A

Strong opioid receptor agonist
* orally active and semisynthetic analog of morphine
* approximately 8-10x more potent than morphine
* Preferred over morphine in patients with renal dysfunction due to less accumulation of active metabolites

19
Q

Describe the characteristics of oxymorphone.

A

Strong opioid receptor agonist
* semisynthetic opioid analgesic
* oral form is 3x more potent than oral morphine
* oral form available in both intermediate-acting and extended-release
* no clinically relevant drug-drug interactions associated with the P450 enzyme system

20
Q

Describe the characteristics of fentanyl.

A

Strong opioid receptor agonist
* synthetic opioid
* has a 100-fold the analgesic potency of morphine
* highly lipophilic
* rapid onset and short duration of action (15-30 mins)
* fentanyl + local anesthetics = epidural analgesia for labor and postop pain
* used in anesthesia for analgesic and sedative effects
* Used in the treatment of cancer patients with breakthrough pain who are tolerant to opioids

21
Q

Describe the characteristics of methadone.

A

Strong opioid receptor agonist
* acts by binding to the u-opioid receptor, but also has affinity for the N-methyl-D-aspartate (NMDA) receptor (a glutamate receptor)
* metabolized by CYP3A4, 2B6, and 2D6, and substrate of the ABCB1 efflux transporter in intestines and brain
* Methadone is used for the treatment of opioid dependency (long-term and short periods w/o withdrawal symptoms)
* Also used analgesic in chronic pain –> more effective against neuropathic pain because of activity with NMDA receptor

22
Q

Describe the characteristics of codeine.

A

Moderate agonist of opioid receptors
* selective agonist of the u-opioid receptor (less effective than morphine)
* functions as a prodrug of its major active metabolite, morphine, catalyzed by CYP2D6
* CYP2D6 activity varies in patients and ultra-rapid metabolizers may experience higher levels of morphine, leading to possible overdose.
* Genetic polymorphisms of the CYP2D6 gene have implication on codeine associated toxicity
* Drug interactions associated with the CYP2D6 enzyme may alter the efficacy of codeine or lead to toxicity

23
Q

Explain the medical uses of codeine.

A
  • pain relief
  • cough depressant
  • diarrhea
24
Q

Describe the characteristics of oxycodone.

A

Moderate agonist of opioid receptors
* semisynthetic derivative of thebaine, an opioid alkaloid found in the opium poppy
* metabolized via CYP2D6 and 3A4, excreted via the kidney
* Used for managing moderate to moderately severe acute or chronic pain
* available as controlled-release tablet, first-line treatment for cancer pain with less side effects than morphine

25
Q

Describe the characteristics of hydrocodone.

A

Moderate agonist of opioid receptors
* methyl ether of hydromorphone (weaker analgesic than hydromorphone, with oral analgesic efficacy similar to morphine
* often combined with acetaminophon or ibuprofen to treat moderate to severe pain
* anti-tussive
* metabolized in the liver by several metabolites (including CYP2D6) –> can be affected by drug-drug interactions

26
Q

Name commone adverse effects of opioid agonists.

A
  • hypertension
  • anxiety
  • sedation
  • constipation
  • urinary retention
  • nausea
  • potential for addiction
  • respiratory depression
27
Q

Name commone adverse effects of opioid agonists.

A
  • hypertension
  • anxiety
  • sedation
  • constipation
  • urinary retention
  • nausea
  • potential for addiction
  • respiratory depression
28
Q

What is the approximate number of drug-involved overdose deaths in 2020?

A

90,000 deaths
* primarily fentanyl

29
Q

What is the approximate number of overdose deaths involving opioids in 2020?

A

around 60,000 deaths

30
Q

Explain opioid use disorder.

A

Opioid use disorder is a problematic pattern of opioid use that causes significant impairment or distress.
* symptoms: strong desire to use opioids, increased tolerance, failure to fulfill obligations, trouble reducing use, and withdrawal syndrome with discontinuation
* addiction and dependence are components
* opioids: heroin, morphine, fentanyl, codeine, oxycodone, and hydrocodone

31
Q

What are some withdrawal symptoms: stage 1, 2, and 3?

A
32
Q

Explain naloxone.

A

Lipophilic compound that acts as a non-selective and competitive opioid receptor antagonist
* highest binding affinity for the u-opioid receptor, then the d-opioid receptor, and lowest for k-opioid receptor
* rapidly displaces all receptor-bound opioid molecules –> reverses the effect of a morphine overdose
* Useful in acute opioid overdose and reducing respiratory or mental epression due to opioids

33
Q
A

C. urinary retention

34
Q
A

E. codeine

35
Q
A

E. hydromorphone

36
Q
A

B. Naloxone

37
Q
A

B. oxymorphone

PHRX 3009: drug action (36 decks)

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