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Block 2 > Opiates > Flashcards

Opiates Flashcards

1
Q

What are opiates?

A

They are endogenous substances -> Acts on receptors that are already in the body.

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2
Q

Mechanism of opiates?

A

Opioid-receptors are all inhibitory (target to inhibit GPCR), just stimulate activity by inhibiting inhibitors.

  • Increase pain inhibitory pathways
  • Decrease transmission of sensory stimulus to brain -> Binds to GPCR to stop nerve firing
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3
Q

Actions of opiates?

A
  • Analgesia (pain killing)
  • Euphoria (Sense of contentment)
  • Impaired cough reflex
  • Constipation
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4
Q

Side-effects of opiates?

A
  • Respiratory depression
  • Nausea and vomiting
  • Dependence/withdrawal
  • Miosis (pupillary constriction)
  • Pruritis (itching)
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5
Q

List and describe opioid receptors

A

kappa-opioid receptor

  • produces analgesia
  • Side effects: dysphoria (unhappiness), hallucination

Delta-opioid receptor

  • Produce analgesia
  • Side effect: seizures

Mu-opioid receptor

  • Main opioid receptor
  • Produce all main opioid actions: strong analgesia, constipation, nausea, respiratory depression, reduced cough reflex
  • inhibited by Naloxone
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6
Q

Explain pain pathway overview:

A
  1. Injury transmits signal through nociceptor
  2. Nociceptor excites spinal cord neuron
  3. Spinal neuron transmits signal to thalamus
  4. Thalamus transmits signal to cortex
  5. Cortex feels how bad it is and where it is
  6. Cingulate cortex and insular cortex say how unpleasant the pain is
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7
Q

Describe descending analgesic pathway

A
  • Periaqueductal gray (PAG) of brain stem receives signal from nociceptors
  • PAG sends signal along neuron to medulla
  • Neuron releases glutamate into medulla
  • Medulla release inhibitory neurotransmitters into spinal cord to block noxious stimuli from nociceptors
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8
Q

Mechanism of analgesic effect of opioids on descending analgesic pathway

A
  • Cell in PAG region produce GABA which inhibit neuron activity to medulla
  • mu-opioid receptors are on GABA producing cells
  • mu-opioid receptors inhibit release of inhibitory GAB, thus activating descending pathway
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9
Q

Inhibition of nociceptors in mechanism of analgesic effect of opioids

A
  • Opioid receptors on nociceptor terminals in spinal cord

- Opioid binding inhibits noxious stimulus of spinal cord

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10
Q

Describe mechanism of euphoria/dysphoria of opioids:

A

mu-opioid receptors produce euphoria (release of dopamine)

  • mu-opioid receptors are on GABA producing cells
  • Inhibit inhibitory GABA release to dopamine releasing neurons.

kappa-opioid receptors produce dysphoria

  • kappa-opioid receptors are on dopamine releasing neurons
  • Inhibit release of dopamine directly
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11
Q

List opioid drugs available

A
  • Morphine
  • Codeine
  • Oxycodone
  • Fentanyl
  • Buprenorphine
  • Methadone
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12
Q

Clinical uses & relative potency of morphine

A
  • Low oral bioavailability (30%)
  • Short half-life
  • Can be administered orally, subcutaneously or epidurally
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13
Q

Clinical uses and relative potency of codeine

A
  • Higher oral bioavailability
  • Less potent than morphine
  • Good for constipation but not analgesia
  • Just a pro-drug of morphine: highly variable metabolism by body, risky to use
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14
Q

Clinical uses and relative potency of oxycodone

A
  • Binds directly to opiate receptors; quite potent
  • Good oral bioavailability (80%)
  • short half-life but can be extended
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15
Q

Clinical uses and relative potency of fentanyl

A
  • Synthetic opioid
  • 80x as potent as morphine
  • Short half-life
  • High affinity to mu-agonist
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16
Q

Clinical uses and relative potency of buprenorphine

A
  • Strong analgesic
  • Less side-effects as morphine
  • Long half-life
17
Q

Clinical uses and relative potency of metadone

A
  • Similar to morphine
  • Little euphoria - used in addict recovery
  • Very long half-life
18
Q

Describe the metabolism of opioids, indicating any enzymes involved

A
  • Highly metabolized in liver

- Codeine is metabolized into morphine with enzyme CYP2D6 in liver: amount of CYP2D6 varies largely

19
Q

List the actions and side-effects of opiates

A

Actions of opiates:

  • Analgesia (pain killing)
  • Euphoria (sense of contentment)
  • Impaired cough reflex
  • Constipation

Side effects:

  • Respiratory depression
  • Nausea and vomiting
  • Dependence/withdrawal
  • Miosis (pupillary constriction)
  • Pruritis (itching)
20
Q

Describe opioid antagonist roles of Naloxone

A
  • used to reverse opioid overdose
  • short acting
  • Low oral bioavailability (very high liver metabolism) - must be injected
  • Competitive antagonist
21
Q

Describe opioid antagonist roles of Naltrexone

A
  • Long acting
  • High oral bioavailability
  • Used to reduce opioid dependency

Block 2 (30 decks)

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