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CPT > Opioids > Flashcards

Opioids Flashcards

1
Q

How is pain formed?

A

1) stimulation of nociceptors
2) release of substance P and glutamate
3) stimulation of afferent nerves
4) decussation of fibres
5) action potential ascends
6) synapse in thalamus
7) project to primary sensory cortex

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2
Q

What are the pain modulators?

A

Peripherally:
Substantia gelatinosa

Centrally:
Peri aqueductal grey

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3
Q

What are examples of endogenous opioids?

A

Enkephalins
Dynorphins
B-endorphins

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4
Q

What receptors do opioids act on?

A

μ - enkephalins, B-endorphins

δ - enkephalins

κ - dynorphins

All GPCRs

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5
Q

What is the WHO analgesic ladder?

A

Simple analgesia - paracetamol, NSAIDs
Weak opioid - codeine
Strong opioid - morphine, fentanyl

Typically used for chronic pain
If acute pain, can go straight to strong opiate

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6
Q

What is the general principles of opioid use?

A

Exploit natural opioid receptors - agonist or antagonism
Mainly act via μ receptors

Aim to modulate pain
Also indicated in cough, diarrhoea and palliation

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7
Q

Describe pharmacokinetics of morphine

A

Absorption:
PO, IV, IM, SC, PR
Erratic gut absorption
Significant first pass

Distribution:
Rapidly enters all tissues, inc foetal

Metabolism:
Morphine + glucuronic acid => M6G + M3G

Elimination:
Renal

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8
Q

What are the actions of morphine?

A

Strong agonist
Bind to μ receptors

Causes analgesia and euphoria

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9
Q

What are some side effects of morphine?

A

Respiratory depression - medullary resp centre made less responsive to CO2
Emesis - stimulates CTZ
Decreased GI motility => constipation
Miosis
Mast cell degranulation => histamine release - be careful w/ asthmatics

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10
Q

Describe pharmacokinetics of fentanyl

A

Absorption:
IV, epidural, intrathecal, nasal
80-100% bioavailability

Distribution:
Highly lipophilic and protein bound
High level of CNS membrane

Metabolism:
CYP 3A4

Elimination:
Half life 6 mins
Renally excreted

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11
Q

What are the actions of fentanyl?

A

Strong agonist

Analgesia
Anaesthetic

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12
Q

What are the side effects of fentanyl?

A

Respiratory depression
Constipation
Vomiting

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13
Q

Describe the pharmacokinetics of codeine

A

Administration:
PO, SC

Metabolism:
Codeine => morphine via CYP 2D6

Elimination:
Glucoronidation of morphine
Renal excretion

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14
Q

What are the actions of codeine?

A

Moderate antagonist

Mild - moderate analgesia
Cough depressant

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15
Q

What are the side effects of codeine?

A

Constipation

Respiratory distress

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16
Q

Describe the pharmacokinetics of buprenorphine

A

Administration:
Transdermal, buccal, sublingual

Distribution:
V lipophilic

Metabolism:
Hepatic via CYP 3A4

Elimination:
Biliary excretion
Therefore safe in renal impairment
Half life 37 hrs

17
Q

What are the actions of buprenorphine?

A

Mixed agonist-antagonist

V high affinity for μ receptor, low Kd

Used for moderate to severe pain
Also used for addiction treatment

18
Q

What are some side effects of buprenorphine?

A

Respiratory depression
Low BP
Nausea
Dizziness

19
Q

Describe the pharmacokinetics of naloxone

A

Absorption:
IV, IM, intranasal, PO
V low bioavailability - extensive first pass metabolism
Rapid onset of action

Distribution:
V lipophilic

Metabolism:
Hepatic => naloxone-3-glucoronide

Elimination:
Renal

20
Q

What are the actions of naloxone?

A

Antagonist

Greater affinity than morphine and fentanyl

Competitive antagonism of opioid

21
Q

What are the side effects of naloxone?

A

Short half life

Tf give slow infusion - pt has time to metabolise morphine

22
Q

How does opioid tolerance occur?

A

When giving synthetic opioids, the number of opioid receptors increases

Requires a higher dose of opioid required to get enough binding for a cell response

23
Q

How does opioid withdrawal occur?

A

Suddenly taking away a synthetic opioid means that there is a lower percentage of binding to receptors

Therefore don’t get a cell response

24
Q

What are the actions of methadone?

A

Used to avoid withdrawal Sx
Binds to opioid receptors
Slowly decrease dose to decrease number of receptors
Removes some side effects

25
Q

What are some special considerations for opioids?

A 
Manual labourers/drivers
Elderly 
Bedbound
Asthmatics
Biliary tract obstruction 
Respiratory disease 
Renal impairment 
Pregnancy
26
Q

What are some contraindications for opioids?

A 
Hepatic Failure 
Acute respiratory distress
Comatose 
Head injuries 
Raised ICP
27
Q

How are opioids prescribed in palliative care?

A

Buprenorphine, diamorphine, fentanyl, morphine and oxycodone all prescribed

Tend to ignore special considerations eg renal impairment

Indications: pain, shortness of breath

Also need to manage side effects like nausea and constipation

28
Q

Why are some opioids controlled drugs?

A

To prevent:
Misuse
Illegal obtainment
Any harm being caused

CPT (21 decks)

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