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Pharmacology (Semester 6) > 8.1 Opioids > Flashcards

8.1 Opioids Flashcards

1
Q

Define nociception and pain

A

Nociception: non-conscious neural traffic in response to (potential) trauma

Pain: an unpleasant sensory and emotional experience associated with actual or potential tissue damage (IASP definition)

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2
Q

Describe some of the ‘multidimentional’ aspects of pain

A
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3
Q

What are the 2 main types of pain and compare these?

A

1) Nociceptive: caused by an inflammatory or non-inflammatory response to an overt or potentially tissue-damaging stimulus
2) Neuropathic pain: caused by a lesion or disease of the somatosensory NS

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4
Q

Give 4 examples of analgesia

A

1) Paracetamol
2) NSAIDS
3) Opioids
4) Adjuvants
5) Placebo

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5
Q

Describe the ‘Who analgesic ladder’ for prescribing pain medication

A
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6
Q

What is the gate control theory of pain?

A

The gate theory of pain suggests that stimulation of non-nociceptive receptors can inhibit transmission of nociceptive information in the dorsal horn.

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7
Q

Describe the gate theory of pain

A

1) Afferent 1o sensory neurones of pain are Aδ or C fibres
2) transmission occurs between 1o and 2o neurones in substantia gelatinosa (dorsal horn, spinal cord)
3) Substance P is released at the synaps
4) Inhibition of transmission comes from:

  • Inhibitory interneurons linked to Aα and Aβ fibres
  • Inhibitory descending pathways from higher brain centres
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8
Q

Describe the pathway of central modulation of pain

A

Periaqueductal grey matter (PAG) in midbrain ➞ through rostroventromedial medulla (RVM) ➞ into spinal cord

down spinal cord to dorsal horn ➞ releases Serotonin & NA which stimulate interneurons to release Enkephalins, beta-endorphins and/or dynorphin

These bind opioid receptors ➞ inhibits the release of substance P between 1st and 2nd order neurones of nociceptive pathways

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9
Q

Give 3 substances which bind opioid receptors

Give 2 substances which bind non-opioid receptors

A

Opioid: Enkephalins, beta-endorphins, dynorphin

Non-opioid: Serotonin and noradrenaline

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10
Q

Define the following:

  1. Opium
  2. Opiate
  3. Opiod
A

Opium: dried powder mixture of 20 alkaloids from unripe seed capsules of the poppy

Opiate: any agent derived from opium

Opioid: substances (exogenous or endogenous) with morphine-like properties

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11
Q

Where do opiods primarily act?

A

Bind to specific opioid receptors in the CNS (spinal cord) to mimic the action of endogenous peptide neurotransmitters ➞ inhibit the transmission of pain

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12
Q

Give 2 examples of the following opiods:

  1. natural
  2. semi-synthetic
  3. sythetic
A

Natural: morphine, codeine, papaverine

Semi-synthetic: hydromorphone, hydrocodone, oxycodone, oxymorphone, buprenorphine

Synthetic: fentanyl, fepridine, methadone, tapentadol, tramadol

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13
Q

What class of receptors are opiod receptors + the 4 types

A

GPCRs ➞ Gi (inhibitory) subtype ➞ located pre and post synaptically

Types:

  • μ mu
  • δ delta
  • κ kappa
  • ORL1 (opioid receptor-like 1) (NOP)
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14
Q

Give the MoA of opiods

A

Gαβγi ➞ Gαi + Gβγi

Pre-synaptic: Gβγi inhibits VOCC ➞ reduces Ca2+ ➞ less NT release

Post-synaptic: Gβγi opens K+ channels ➞ K+ efflux ➞ hyperpolarised + less excitable cells

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15
Q

Give an example of an opiod which is an:

  1. full agonist
  2. partial agonist
  3. antagonist
A

Agonist: Morphine

Partial agonist: Buprenorphine

Antagonist: Naloxone

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16
Q
A
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17
Q

What is considered the ‘gold standard’ opiod?

A

Morphine

18
Q

Give 4 routes of morphine administration

A

PO, IM, IV, SC, nebulized, rectal, epidural, intrathecal

19
Q

Morphine is a PCA, what does this mean?

A

patient controlled analgesic

20
Q

Describe morphines absorption in the gut and 1st/2nd pass metabolism

A

Well absorbed from the gut and undergoes extensive first-pass metabolism (oral bioavailability ~25%)

21
Q

Give the 2 metabolites of morphine and state their clinical relevance

A

Metabolites: morphine-6-glucuronide and morphine-3-glucuronide

Metabolites can be measured in urine, useful for screening

22
Q

Give the chemical name and common name of Diamorphine?

A

Chemical: Diacetyl morphine

Common: Heroin

23
Q

Diamorphine undergoes a _______ reaction to form the intermediate _______. This is then converted into morphine.

A

hydrolysis, monoacetyl morphine

24
Q

Compare the t1/2 of diamorphine and morphine

A

Diamorphine: t1/2 = 5mins

Morphine: t1/2 = 4 hours

25
Q

Codeine is a _____ opioid at the ____ receptor hence has mild analgesic properties (oral). It is metbaolised in the body to ______ by the CYP______ enzymes and can therfore be affected by polymorphisms in this cytochrome class.

A

weak, mu, morphine, CYP2D6

26
Q

Codeine acts as an effective analgesia in what region of the CNS

A

spinal and supraspinal level

27
Q

How does codeine cause sedation and euphoria

A

Effect on midbrain dopaminergic, serotoninergic and noradrenergic nuceli

28
Q

What effect does codeine have on bowel movements?

A

Decrease in motility, increase smooth muscle tone (constipation)

29
Q

Why does codeine cause depression of cough reflex?

A

Codeine and morphine have antitussive properties

30
Q

???

A
31
Q

What 3 opioid drugs are commonly used in anaesthetics?

What is a common ADR of these?

A

Fentanyl, alfentanil, remifentanil

ADR: can cause histamine release

32
Q

Which analgesia is commonly used in labour?

Why should it NOT be given in frequent repeated doses?

A

Pethidine (IM)

Frequent doses can cause accumulation of metabolite which can lead to convulsions

(Pethidine ➞ norpethidine (metabolite) ➞ convulsions)

33
Q

Why do opiods cause repiratory depression?

A

There are μ receptors in the respiratory-centre of the brain stem ➞ hypercapnic drive

34
Q

Why can opiods cause nausea and vomiting?

A

Central effect on chemoreceptors trigger zone in medulla

35
Q

Why may opiods cause constipation

A

Increased SM tone and decreased motility ➞ spasm of sphincter of Oddi ➞ constipation

36
Q

How may opiods cause bradycardia and hypotension?

A

Bradycardia: decreased SNS drive + direct effect on SAN

Hypotension: Histamine release ➞ decrease TPR and reduced baroreceptor reflex

37
Q

Why may opiods cause pruritis?

A

Histamine release from mast cells

38
Q

Hallucinations are most common with which opiods?

A

k agonists (but morphine and other μ agonists may also cause hallucinations)

39
Q

Why may Miosis be seen with opiod use?

A

μ and κ receptors in occulomotor nerve are stimulated by opioids resulting in constriction of the pupils

40
Q

Give 2 other undesirable symptoms experienced with opiod use?

A

Drowsiness and Dysphoria

41
Q

Why can opiod use lead to dependence/tolerance?

A

Down regulation of opioid receptors or decreased production of endogenous opioids

42
Q

Describe the legal requirements for prescribing controlled drugs?

A

Pharmacology (Semester 6) (17 decks)

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