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Neuropharmacology > Opioid Analgesics > Flashcards

Opioid Analgesics Flashcards

1
Q

What are the best defined peptides?

A
  • opioid peptides e.g. β-endorphin, met/leo-enkephalin and dynorphin
  • substance P
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2
Q

What is substance P?

A

mediator of slow EPSPs in nociceptive CNS sensory pathways

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3
Q

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

A
  • β-endorphin from pre-proopiomelanocortin (POMC)
  • enkephalins from pre-proenkephalin
  • dynorphins from pre-prodynorphin
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4
Q

What can influence the perception of pain?

A

attitude, mood and physical exercise

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5
Q

What parts of the brain process and interpret pain signals?

A

thalamus and cortex

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6
Q

What does the limbic system influence?

A

the emotional response of pain, often generating feelings of discomfort, anxiety, or distress

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7
Q

How does opioid analgesia work?

A

it plays on endogenous mechanisms to inhibit the propagation of pain signals, alter the emotional perception of pain and elevate the pain threshold

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8
Q

What are opioid analgesics used for?

A
  • acute pain e.g. post-surgical pain
  • chronic pain management, particularly for cancer-related pain or palliative care
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9
Q

What are the 3 main sites of opioid receptors regulating pain?

A
  • peripheral nociceptive terminals
  • spinal cord (dorsal horn)
  • brain (PAG, thalamus and cortex)
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10
Q

What are the 3 major opioid GPCRs and what are they responsible for?

A
  • mu – analgesic effects and side effects like euphoria, respiratory depression, and physical dependence
  • delta – modulates pain and mood, and has a role in analgesia (less than mu receptor); may also influence antidepressant effects
  • kappa – modulates pain, but activation can also produce dysphoria and hallucinations; plays a role in the body’s response to stress and controls some anti-inflammatory effects
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11
Q

How do opioids inhibit neurotransmitter release?

A
  • inhibiting calcium entry
  • enhancing potassium efflux
  • inhibiting AC which converts ATP to cAMP
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12
Q

How does opioid analgesia cause euphoria?

A

they bind to Mu receptors in the VTA and nucleus accumbens and inhibit the release of GABA, which leads to an increase in dopamine levels in reward circuits

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13
Q

What is dopamine a precursor of?

A

noradrenaline

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14
Q

When is dopamine inhibitory?

A

via GPCR activation of potassium channels

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15
Q

How is dopamine activity increased and decreased respectively?

A
  • increased by CNS stimulants and anti-parkinson drugs
  • decreased by antipsychotics
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16
Q

What is D2?

A

the main dopamine subtype in basal ganglia neurons widely distributed at the supraspinal level

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17
Q

Give examples of dopaminergic pathways

A
  • nigrostriatal (motor control)
  • mesolimbic (emotional and drug-induced reward systems)
  • tuberoinfundibular tracts (pathway from hypothalamus to pituitary glands that controls secretions)
18
Q

What are clinical uses of opioid agonists?

A
  • analgesia e.g. codeine, morphine, pethidine
  • anaesthetic adjuvant e.g. fentanyl
  • cough suppressant/antitussive e.g. codeine
  • anti-diarrhoeal e.g. diphenoxylate, loperamide
19
Q

Describe morphine as an opioid agonist (strength, which receptors, analgesic affinity and liability for abuse)

A
  • strong agonist
  • highest affinity for Mu receptor (some affinity for Delta and Kappa)
  • high maximum analgesic affinity
  • high liability for addiction/abuse
20
Q

Describe methadone and fentanyl as opioid agonists (strength, which receptors)

A
  • strong agonists
  • highest affinity for Mu receptor (no affinity for Delta and Kappa)
21
Q

What is fentanyl used as?

A

an anaesthetic adjuvant

22
Q

Describe codeine as an opioid agonist (strength, which receptors, analgesic affinity and liability for abuse)

A
  • moderate agonist
  • weak affinity for Mu and Delta receptors
  • low maximum analgesic affinity
  • moderate liability for addiction/abuse
23
Q

What happens to 10% of codeine?

A

it is converted to morphine/dihydromorphine

24
Q

Why do 10% of the population show reduced analgesic effects to codeine?

A

lack of demethylating enzyme

25
Q

What is tramadol?

A

a weak Mu agonist and a weak inhibitor of 5-HT (serotonin) and noradrenaline reuptake

26
Q

Describe buprenorphine as an opioid agonist (strength, which receptors, analgesic affinity and liability for abuse)

A
  • mixed agonist-antagonist
  • strong Mu partial agonist and Kappa antagonist
  • high analgesic affinity
  • moderate liability for addiction/abuse
27
Q

Describe nalbuphine as an opioid agonist (strength, which receptors, analgesic affinity and liability for abuse)

A
  • mixed agonist-antagonist
  • weak Mu antagonist and Kappa agonist
  • high analgesic affinity
  • moderate to low liability for addiction/abuse
28
Q

What are opioid antagonists used for?

A

to counteract opioid overdose

29
Q

Give examples of opioid antagonists and their route of administration

A
  • naloxone – short-acting, usually intravenous administration
  • nalmefene – long-acting usually intravenous administration
30
Q

Why are opioid antagonists used with caution in patients with opiate dependency?

A

they can precipitate potentially fatal withdrawal syndrome

31
Q

What does neuropathic pain usually require?

A

higher opioid doses than nociceptive pain

32
Q

How should opioid analgesics be used?

A

started at a low dose and carefully titrated until an adequate level of analgesia is obtained, or until persistent and unacceptable side effects warrant a reevaluation of therapy

33
Q

When can respiratory depression be lethal?

A
  • overdose
  • respiratory disease
  • hepatic dysfunction
  • combination with other CNS depressants
  • young children
34
Q

How can opioids cause respiratory depression?

A

they act on the nucleus tractus solitarius and nucleus ambiguus which reduces responses to CO2 (and H+) and suppresses voluntary breathing

35
Q

Where does respiratory depression occur?

A

largely in opioid-naïve patients

36
Q

What are common adverse effects of opioids?

A
  • nausea/vomiting – due to actions on the chemoreceptor trigger zone in the area postrema of the medulla
  • drowsiness
  • constipation – due to reduced GI motility
37
Q

What are less common adverse effects of opioids?

A
  • miosis (pinpoint pupils) – due to actions in the oculomotor nucleus
  • urinary retention – due to increased bladder sphincter tone
  • postural hypotension and bradycardia – due to actions in cardio-regulatory nuclei in the medulla
  • immunosuppressant effect with long term use
38
Q

What does hisatamine release triggered by morphine cause?

A

causes itching, bronchoconstriction and hypotension due to vasodilation

39
Q

What are possible withdrawal symptoms of opioids?

A

anxiety, irritability, chills, hot flushes, joint pain, lacrimation, rhinorrhoea, nausea, abdominal cramps and diarrhoea

40
Q

What are the strong opioid agonists?

A

morphine, methadone and fentanyl

41
Q

What are the moderate opioid agonists?

A

codeine and tramadol

42
Q

What are the mixed opioid agonists and antagonists?

A

buprenorphine and nalbuphine

Neuropharmacology (12 decks)

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