Opioid Analgesics Flashcards

1
Q

Where do opioids exert their effect?

A

The CNS, but also in the periphery.

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2
Q

What is Gate theory?

A

Opites act as a gate between dorsal root of spinal cord and the thalamus and primary sensory cortex, to prevent the signal from the sesory receptor being noticed

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3
Q

What endogenous opioids does the body produce?

A

Enkephalins
Endorphins
Dynorphins

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4
Q

Where do endogenous opioids come from?

A

Cleaved from precursors - proenkephalin, POMC, and prodynorphin

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5
Q

What opioid receptors are present through the body?

A

M (mu) receptors
Delta receptors
K (kappa) receptors

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6
Q

What binds to delta receptors?

A

Enkephalins in the brain, CNS, and at the NMJ.

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7
Q

Where are K receptors found?

A

The spinal cord

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8
Q

Where are M receptors found?

A

Supraspinally.

Also in lymphocytes which is why opiates long term have an immunosuppressive effect.

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9
Q

What kind of receptors are opioid receptors?

A

GPCRs

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10
Q

What is the general effect that activating a opioid receptor has?

A

Increased efflux of K+ causing decreased excitability

Also decreased Ca2+ influx and cAMP synthesis

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11
Q

What effect does decreasing Ca2+ influx have?

A

Decreased release of neurotransmitter into the synaptic cleft

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12
Q

Which receptor are most opiate ADRs associated with?

A

M receptors

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13
Q

What ADRs are associated with M receptors?

A
N&V
Constipation
Drowsiness
Miosis
Dependance
Tolerance
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14
Q

What ADRs are generally associated with all opioid receptors?

A

Respiratory depression

Hypotension

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15
Q

What ADRs are associated with K receptors?

A

Dysphoria (esp. with pentazocine)

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16
Q

How do opiate drugs work?

A

All fairly differently to each other

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17
Q

How does morphine work?

A

As a receptor agonist

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18
Q

How does bupranorphine work?

A

As a partial agonist

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19
Q

How does nalbuphine work?

A

As an agonist at some receptors, and an antagonist at others

20
Q

How does naloxone work?

A

As an antagonist - used to reverse respiratory depression.

21
Q

Tell me about morphines pharmacokinetics?

A

T1/2 ~ 4.5 hours

Oral bioavailability 25% so more effective if given IV.

22
Q

What is the half life of diamorphine?

A

0.08 hours = about 5 minutes

23
Q

What is methadone used for?

A

Maintenance in opiate dependancy

24
Q

Tell me about the pharmacokinetics of methadone?

A

T1/2 = 1.9-3.9 hours

90% oral bioavailability if given as a syrup.

25
Q

What is the t1/2 of bupranorphine?

A

2-4 hours

26
Q

Tell me about codeine.

A

T1/2 = 2-4 hours.

90% oral bioavailability.

27
Q

What is the gold standard opiate?

A

Morphine!

28
Q

How is morphine metabolised?

A

Phase 2 glucuronidation in th liver to its also active metabolite which prolongs the effective t1/2.

29
Q

How are the metabolites of morphine excreted? Why is this important?

A

Via urine. A urine screen can be used to look for morphine use.

30
Q

Compare the structure of morphine and diamorphine.

A

Morphine is tricyclic with 2 polar groups, so is water soluble.
Diamorphine has 2 acetyl groups so is much more lipid soluble.

31
Q

What is good about diamorphine?

A

It crosses the BBB rapidly and effectively, so gives you a big ol hit of morphine straight to the brain.

32
Q

What is diamorphine metabolised to?

A

Morphine!

33
Q

What do we use opiates for generally?

A

Analgesia for moderate to severe pain

34
Q

What are opiates bette for, visceral pain or sharp stabby pains?

stabby stabby 🔪

A

Visceral pain

Did i catch you out with that lil ol knife?

🔪 stabby stabby

35
Q

What kind of pain setting is morphine used in often?

A

Terminal illness and palliative care

36
Q

When is tramadol used?

A

Analgesia, with slight antidepressant effect

37
Q

What kind of analgesic is codeine?

A

Mild but metabolises to morphine

38
Q

Why do people respond differently to codeine?

A

Metabolised to morphine by CYP2D6 which is highly polymorphic.

39
Q

Which population tends to have a less effective CYP2D6 and therefore respond poorly to codeine?

A

Chinese populations

40
Q

What are fentanyl, afentanil, and remifentanil?

A

Anaesthetics ~100-1000 times more potent than morphine

41
Q

What is pethidine used for?

A

IM pain relief if labour

42
Q

Can you give pethidine over and over?

A

Noop, because its metabolite can cause convulsions.

43
Q

What are the agonist-antagonists?

A
Pentazocine
Nalbuphine
Butorphanol
Buprenorphine
Meptazinol
44
Q

What are the antagonists to opioid receptors?

A

Naloxone

Naltrexone

45
Q

What is the medicolegal aspect to opiates?

A

Some are controlled drugs under the 1971 and 2001 acts.

46
Q

Which are the main controlled opiates?

A
Diamorphine
Morphine
Remifentanil
Pethidine
Certain preparations of codeine