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Pharmocolgy > P9: Opiate Analgesics > Flashcards

P9: Opiate Analgesics Flashcards

1
Q

What is an analgesic

A

What receptor subtypes do selective direct acting sympathomimetics act on

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2
Q

What are the 3 main classes of analgesic

A
  • Opioids
  • Non-steroidal anti-inflammatory drugs (NSAIDs)
  • Local Anaesthetics
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3
Q

Give examples of non-steroidal anti-inflammatory drugs (NSAIDs)

A

Aspirin
Ibuprofen
Diclofenac

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4
Q

Give examples of local anaesthetics

A

Lidocaine
Novocaine
Benzocaine

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5
Q

Why is paracetamol not truly an NSAID

A

Has no appreciable anti-inflammatory activity

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6
Q

What is opium

A

dried poppy latex, complex mix of analgesic, non-analgesic and inert agents

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7
Q

What are opiates

A

Drugs derived from opium and semi-synthetic agents from them and from thebaine

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8
Q

What are opioids

A

All agonists and antagonists with morphine like pharmacology

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9
Q

What are the 5 classes of opioid receptors

A 
μ - 1 and 2 - mu
κ - 1, 2 and 3 - kappa
δ - 1 and 2 - delta
NOP/nociceptin
ζ - zeta
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10
Q

What receptors are involved in opioid analgesic actions

A

μ, κ and δ

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11
Q

What class of receptor are all opioid receptors

A

7 TMD GPCRs

acting through Gi/o

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12
Q

Give examples of agonist opioid drugs

A
  • Morphine, Codeine and Heroin (opiate agonists)
  • Pethidine, Fentanyl and Methadone (synthetic opioid agonists)
  • Endorphins, enkephalins (endogenous agonists)
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13
Q

Give an example of antagonist opioid drugs

A

Naloxone

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14
Q

How can nalorphine and pentazocine act as both opioid agonist and antagonists

A

Different actions on different receptors - competitive μ antagonists and κ agonists

Dose-dependent effects

Agonists at high temperatures

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15
Q

Name a partial opioid agonists

A

Buprenorphine - partial μ agonist, much more potent than morphine but lower max effect, blocks morphine actions

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16
Q

What pain fibres is opioid analgesia more effective on

A

C fibres = continuous dull pain

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17
Q

Describe the mechanism of descending pain control in opioid analgesia

A
  • Periaqueductal gray matter (PAG) sends inhibitory GABAergic projections to the midline raphe nucleus (MRN) and locus coeruleus (LC)
  • the MRN and LC send inhibitory 5-HT and NA projections to the substantia gelatinosa in the spinal cord, limiting nociceptive fibre transmission
  • opioids act on μ receptors in the PAG and inhibit GABA outflow, relieving inhibition of 5HT and NA and suppressing pain signalling
18
Q

Describe the mechanism of the spinal actions in opioid analgesia

A
  • Opioids directly stimulate inhibitory interneurons in the spinal cord
  • μ receptors on the C fibre are stimulated by the opioid
  • suppress excitatory neurotransmitter release directly onto the second order neuron, and inhibitory signalling on to the inhibitory interneuron
  • together this suppresses transmission of nociceptive information into the brain
19
Q

What mechanism is thought to cause the euphoria from opioids

A

Stimulation of the ventral tegmental area causing the release of dopamine in the nucleus accumbens and frontal cortex

20
Q

How can opioids result in respiratory depression

A
  • Reduces responsiveness of brainstem centres to plasma partial pressure of CO2
  • Depresses activity in the pontine and medullary centres involved in breathing rhythm and depth
21
Q

Why are high doses of opioid lethal

A

Respiratory depression leading to hypoxia and cardiovascular collapse

22
Q

How can morphine and μ/κ agonists cause miosis

A

They cause miosis (pupillary constriction) by excitatory action at the occulomotor nucleus, activating parasympathetic innervation of the pupil.

23
Q

Opioids are anti-tussive, what does this mean

A

Means they suppress cough reflex

24
Q

NOTE BRUH

A

Codeine and pholcodine are potent anti-tussives but weaker analgesics

25
Q

What are the effects of Opioids on the stomach

A

Decreased gastric motility and delayed emptying time

26
Q

What are the effects of opioids on the small intestine

A
  • Decreased biliary, pancreatic and intestinal secretion
  • Smooth muscle resting tone increased
  • Decreased peristalsis
27
Q

What are the effects of opioids on the large intestine

A
  • Similar to the small intestine
  • significant faecal desiccation
  • anal spincter tone increased
28
Q

What are the overall effects of opioids on the GI tract

A
  • Constipation
  • Delayed digestion of food in the small intestine
  • Retarded absorption of other drugs
29
Q

Where is the chemoreceptor trigger zone (CTZ)

A

Floor of the 4th ventricle, in the area postrema of the medulla.
Outside the BBB, monitors blood chemistry via many different receptors.

30
Q

What inputs does the Vomiting centre get

A

From the CTZ
Vestibular tract input +
GI tract input ( via the nucleus tractus solitarius)

31
Q

How do opioids induce emesis and nausea

A

Direct stimulation of the CTZ in the area postrema of the medulla

32
Q

What is used to reduce opioid induced emesis

A

anti emetics e.g. Domperidone (D2 antagonist) or H1 antagonists

33
Q

How are opioids administered

A
  • IV injection for pain relief

- Oral produces less effect due to first pass but preferred for chronic pain control

34
Q

How is morphine metabolised

A

Conjugated with glucuronic acid in the liver to form inactive morphine-3-glucuronide and extra hepaticallly to form highly active morphine-6-glucuronide

35
Q

How is morphine excreted

A

Via kidneys primarily as 3-glucuronide form

36
Q

Why is morphine not given to neonates and what is used instead

A

Neonates have compromised conjugation mechanisms

Pethidine used instead

37
Q

Give possible mechanisms for opioid tolerance

A

Receptor down regulation
Reduced affinity for the the opioid receptor
Increased metabolism
Inhibition of endogenous opioid release

38
Q

What is physical dependence

A

Associated with withdrawal syndrome, resembles severe influenza - pupillary dilation, sweating, fever, piloerection, nausea, diarrhoea and insomnia

39
Q

What is psychological dependence

A

Craving of drug irresepective of warding off withdrawal symptoms or for its euphoric effects

40
Q

NOTE

A

Opioid tolerance is reach quickly so larger doses needed, easily becomes toxic

Pharmocolgy (22 decks)

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