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Neuropharmacology > Opioids > Flashcards

Opioids Flashcards

1
Q

Name 6 pure agonist of opioid receptor

A
  1. codeine
  2. methadone
  3. etorphine
  4. morphine
  5. fentanyl
  6. pethidine
    -> all high affinity for mu receptors
    -> varying affinity for delta and kappa receptors
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2
Q

Name 3 partial agonist/ mixed agonist-antagonist

A
  1. buprenorphine - high mu affinity but partial agonist
  2. nalorphine - mu antagonist
  3. pentazocine - mu antagonist
    -> diminish analgesia by full agonist
    -> k agonist: dysphoria
    -> reduce side effects
    -> can be used to control mild pain as k agonist (latter two)
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3
Q

Name 2 opioid antagonist and their effects

A
  1. naloxone
  2. naltrexone
    -> block effect of opioids
    -> precipitate severe abstinence syndrome in addicts
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4
Q

Overall MOA of opioids

A
  1. reduce presynaptic release
  2. hyperpolarization of postsynaptic neurons
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5
Q

MOA in spinal cord dorsal horn

A
  1. presynaptic neuron terminal: mu, delta, kappa receptors -> lower Ca2+ influx -> less presynaptic neurotransmitter release
  2. postsynaptic neuron: mu receptor -> K+ efflux -> hyperpolarizaton
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6
Q

MOA in brainstem

A
  1. GABA inhibitory interneuron/ terminal:
    - bind mu receptor on it -> removes its inhibition on the downstream pain inhibitory neuron -> activation of the pain inhibitory neuron
  • the pain inhibitory neuron goes from PAG to nucleus raphe magnus -> release 5-HT and enkephalin at dorsal horn
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7
Q

Functional effect of opioids receptor with elaboration

A
  1. euphoria
  2. dysphoria
  3. sedation and drowsiness
  4. respiratory depression
  5. cough supression
  6. nauseant and emetic effect
  7. miosis
  8. tolerance, addiction, dependence
  9. GI effects: increase resting tone but decrease motility
  10. histamine release
  11. CV effects: vasodilation & bradycardia
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8
Q

State 11 functional effects of opioid receptors

A
  1. euphoria
  2. dysphoria
  3. sedation and drowsiness
  4. respiratory depression
    -> direct effect on brainstem resp centre
    => usual cause of death from morphine
  5. cough suppression
    -> direct effect on cough centre in medulla
  6. nauseant and emetic
    -> direct stimulation of chemoreceptor trigger zone in area postrema of medulla
  7. miosis
    -> pinpoint pupil - characteristic of opioid use
    -> removal of cortical inhibitory action on Cn3 -> increased parasym. tone
  8. tolerance, dependance, addiction
  9. GI effects: increase m. resting tone but decrease motility -> delay gastric emptying -> constipation
    -> biliary colic (increase intraluminal pressure)
  10. histamine release
  11. cardiovascular effects:
    - vasodilation
    - impair sym. vascular reflex: veno and arteriolar dilation
    - stimulate vagal center: bradycardia
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9
Q

State morphine metabolism and hence contraindicated use in what person

A
  1. glucuronic conjugation in liver (p450) -> urinary excretion
    -> morphine 6 glucuronide - more active analgesia
  2. neonates: low level of conjugating enzyme
    -> avoid morphine cogeners in neonates and childbirth
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10
Q

State acute and chronic adverse effects

A

acute:
1. resp depression
2. nausea and vomitting
3. constipation
4. sedation and mental clouding
5. itching

chronic:
1. tolerance
2. dependance

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11
Q

Pharmacological effects with minimal tolerance

A
  • miosis
  • constipation
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12
Q

Mechanism of tolerance

A
  • prolonged agonist stimulation
  • endocytosis of receptors (GPCR internalization)
    -> loss of receptors on cell surface
    -> desensitization and dev of tolerance
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13
Q

Physical symptoms of abstinence syndrome due to dependence

A
  1. sweating, fever
  2. piloerection
  3. yawning
  4. pupillary dilation
  5. nausea/ diarrhoea
  6. insomnia
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14
Q

Symptoms of acute opioid poisoning and treatment

A

Symptoms:
1. unconsciousness
2. pupillary constriction
3. resp depression

Treatment:
- intravenous naloxone injection
-> acute withdrawal syndrome in addicts

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15
Q

Heroin/ diamorphine

A
  • rapidly convert to morphine and 6 monoacetylmorphine
  • strong agonist
  • more lipid soluble than morphine -> enter CNS rapidly
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16
Q

Etorphine

A
  • very strong agonist (x100 than morphine)
  • immobilize wild animals
  • injectable naloxone must be avavilable (in case potential human exposure)
17
Q

codeine

A
  • weak agonist for mild pain
  • marked antitussive action
  • often pair with paracetamol
  • metabolize to morphine in liver by 2D6
18
Q

pethidine / meperidine

A
  • strong agonist
  • anti muscarinic: confusion
  • useful in labour: rapid clearance, not delay labour
  • n-demethylation -> norpethidine => hallucinogenic and convulsant
  • block neuronal uptake of serotonin
19
Q

fentanyl

A
  • strong agonist
  • short duration of action
  • transdermal patch: high abuse potential and risk of overdose
20
Q

methadone

A
  • strong agonist
  • longer duration of action: extensive plasma protein binding
  • clinically used to treat opioid addiction
    -> due to more prolonged & smooth effect but slower onset
    -> less severe physical abstinence syndrome
21
Q

tramadol

A
  • opioid substitute
  • weak mu receptor agonist and potency
  • inhibitor of 5HT and NA reuptake -> the main mechanism for its analgesia
  • weakly antagonised by naloxone
22
Q

buprenorphine

A
  • partial mu receptor agonist
  • strong binding to receptor
    -> more resistant to naloxone reversal
    -> displace morphine/ stronger opioids fro receptors
    => withdrawal syndrome in opioid addicts
  • very lipid soluble (sublingual and transdermal)
23
Q

pentazocine

A
  • mixed agonist antagonist (mu receptor antagonist)
    -> reduce analgesia if concurrent with morphine
    -> withdrawal syndrome in heroin addict
24
Q

Drug interaction

A
  1. sedative-hypnotics: increase CNS and resp depression
  2. antipsychotics tranquilizers: compete for conjugating enzyme -> increased CNS depression
  3. monoamine oxidase inhibitor
    -> contraindication to all opioids analgesics
    -> intensity toxicity due to CYP450 inhibition by MAOI

-> serotonin syndrome when pethidine used with MAOI

25
Q

Contraindication in what people

A
  1. pulmonary failure and asthma
  2. severe hepatic and renal disease
  3. cranial trauma, increased intracranial pressure
26
Q

Name 6 non-opioid drugs for pain relief

A
  1. paracetamol
    NSAIDs:
  2. aspirin
  3. ibuprofen
  4. indomethacin -> most likely to cause adverse GI effect
  5. diclofenac
26
Q

Name 6 non-opioid drugs for pain relief

A
  1. paracetamol
    NSAIDs:
  2. aspirin
  3. ibuprofen
  4. indomethacin -> most likely to cause adverse GI effect
  5. diclofenac

Neuropharmacology (6 decks)

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