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Anaesthetics > Narcotic Analgesics (Opioid) > Flashcards

Narcotic Analgesics (Opioid) Flashcards

1
Q

What are the chemical classes?

A
  • Phenanthrenes
  • Benzylisoquinolines
  • Tetrahydroisoquinolines
  • Cryptopines
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2
Q

Examples of Phenanthrenes?

A
  • Morphine (strong agonist)
  • Codeine (weak agonist)
  • Thebaine (precursor for synthesis of naloxone, buprenorphine and others)
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3
Q

What are the precursors of 3 major families of endogenous opioid peptides?

A
  • B-endorphin from preproopiomelanocortin
  • Enkephalins from preproenkaphalin
  • Dynorphins from preprodynorphin
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4
Q

Endogenous mechanisms

A
  • Inhibit propagation of pain signals
  • Alter emotional perception of pain
  • Elevate pain threshold?
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5
Q

What are the sites of opioid receptors regulating pain?

A
  • Peripheral nociceptive terminals (peripheral analgesia)
  • Spine (spinal analgesia)
  • Brain (supraspinal analgesia)
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6
Q

What are the three major opioid receptor types?

A
  • μ (mu)
  • δ (delta)
  • κ (kappa)

G-protein coupled receptors

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7
Q

What are the effects of opioids and where do they come from?

A
  • Nociceptive terminals: peripheral analgesia (+++)
  • Spine: spinal analgesia (+++)
  • Brainstem: supraspinal analgesia (++), sedation (+) , severe sedation (—)
  • Emotional brain: Euphoria (-), dysphoria (–)
  • Oculomotor: Pupil constriction (–)
  • GI tract: reduced gut motility (-), constipation (–)
  • Respiratory nuclei: cough suppression (++), respiratory depression (—)
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8
Q

Difference between dosage of elderly and younger patients

A

Elderly patients usually require lower dose to achieve effective pain relief than younger patients

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9
Q

Difference between dosage of neuropathic and nociceptive pain

A

Neuropathic pain usually require higher opioid doses than nociceptive pain

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10
Q

How should opioid analgesics be given?

A

Start at a low dose and carefully titrated until an adequate level of analgesia is obtained or until persistent and unacceptable side effect warrant a re-evaluation of therapy

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11
Q

Examples of clinical analgesia opioid agonists

A

Codeine, morphine, pethidine

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12
Q

Examples of clinical anaesthetic adjuvant opioid agonists

A

Fentanyl

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13
Q

Examples of clinical cough suppressant/antitussive opioid agonists

A

Codeine

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14
Q

Examples of clinical anti-diarrhoeal opioid agonists

A

diphenoxylate

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15
Q

Describe morphine

Receptor agonism, analgesic efficacy, liability for addiction/abuse

A
  • Strong μ agonist (weaker κ and δ agnoist)
  • High maximum analgesic efficacy
  • High liability for addiction/abuse
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16
Q

Describe methadone and fentanyl

Receptor agonism, analgesic efficacy, liability for addiction/abuse

A
  • Strong μ agonist (no sigificant κ and δ affinity)
  • High maximum analgesic efficacy
  • High liability for addiction/abuse
  • Methadone is long-acting (plasma half life >24h)
  • Fentanyl is short-acting (anaesthetic adjuvant(
17
Q

Describe pethidine

A
  • Strong μ agonist (probably κ and δ agonist)
  • Shorter duration of action than morphine (esp. in neonate so used in labour)
18
Q

Effects of pethidine

A
  • N-demethylated in liver to norpethidine (hallucinogenic and convulsant effects at high dose)
  • Restlessness rather than sedation
  • Antimuscarinic: dry mouth, blurring of vision but no miosis and less spasm of smooth muscle
19
Q

Describe codeine/dihydrocodeine

Receptor agonism, analgesic efficacy, liability for addiction/abuse

A
  • Weak μ and δ agonist (probably not a κ agonist)
  • Low maximum analgesic efficacy
  • Moderate liability for addiction/abuse
20
Q

Describe tramadol

A
  • Weak μ agonist
  • Weak inhibitor of 5-HT and noradrenaline uptake
21
Q

What is the most serious side effect?

A

Respiratory depression

22
Q

Mechanism that leads to respiratory depression

A

Actions in nucleus tractus solitarius and nucleus ambiguus reduces responses to CO2 and suppress voluntary breathing

23
Q

Respiratory depression can be lethal in…

A

Overdose, respiratory disease, hepatic dysfunction, combination with other CNS depressants, young children

24
Q

What are the common adverse effects?

A
  • Nausea/vomiting: chemoreceptor trigger zone in area postrema of medulla
  • Constipation: reduced gastrointestinal motility
  • Drowsiness
25
Q

What are other adverse effects?

A
  • Miosis: actions in oculomotor nucleus (pinpoint pupil is diagnostic feature of overdose but mydriasis can follow if hypoxia occurs)
  • Urinary retention: increased bladder sphincter tone
  • Postural hypotension and bradycardia: cardioregulatory nuclei in medulla
  • Immunosuppressant: long-term use through CNS effects
  • Histamine release from mast cell (morphine) -> urticaria and itching, bronchoconstriction, hypotension due to vasodilation
26
Q

Manifestations of opioid withdrawals

A

Anxiety, irritability, chills, hot flushes, joint pain, lacrimation, rhinorrhea, nausea, vomiting, abdominal cramps, diarrhoea

27
Q

Example of opioid antagonist

A

Naloxone (short-acting, IV)/Naltrexone (long-acting, oral)/Nalmefene (long-acting, IV)

  • Strong μ antagonism (also κ and δ antaognism)
28
Q

What is opioid antagonists used for?

A

Counteract opioid overdose

Anaesthetics (3 decks)

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