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2.3 Opioids Flashcards

1
Q

Draw the Steps involved in pain pathway

A

page 50/353 of regional book

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2
Q

Analgesics Sites of action / mechanism / examples

Transduction

A

Transduction:

act at the site of injury
and prevent action of
inflammatory mediators

NSAIDs
Antihistaminics
Membrane-stabilising agents
Opioids
Bradykinin and serotonin antagonists
Local anaesthetics
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3
Q

Analgesics Sites of action / mechanism / examples

Transmission

A

Transmission:

alter nerve conduction

Local anaesthetics

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4
Q

Analgesics Sites of action / mechanism / examples

Modulation:

A

Modulation:

modify spinal and supraspinal modulation

Intrathecal and epidural opioids
α2 Agonists NMDA antagonists:

ketamine,
magnesium,
tramadol

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5
Q

Analgesics Sites of action / mechanism / examples

Perception:

A

Perception:

act centrally to reduce perception

Parenteral opioids
α2 Agonists
General anaesthetics

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6
Q

Analgesics Sites of action x4

A

Transduction

Transmission

Modulation

Perception

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7
Q

Opioid receptors are what type

A

Opioid receptors are a

group of G protein–coupled receptors
with .

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8
Q

what are their ligands

A

opioids as ligands

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9
Q

Name endogenous opioids

A 
The endogenous opioids are 
dynorphins, 
enkephalins,
endorphins 
and nocioceptin.
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10
Q

Are receptors localised to central tissues

A 
Opiate receptors are 
distributed widely in the
brain, 
spinal cord 
and peripheral tissues.
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11
Q

Name the opioid receptors

A

OP1 - Kop

OP2 - Dop

OP3 - Mop

OP4 - Nop

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12
Q

Receptor Endogenous Desirable Undesirable

OP1

A

OP1
(KOP/Ќ)

Dynorphin
β- Endorphin

Analgesia

Dysphoria, psychomimetic effects, dieresis

KOP inhibits descending inhibitory pathways, hence is anti-analgesic

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13
Q

Receptor Endogenous Desirable Undesirable

OP2

A

OP2
(DOP/δ)

Enkephalin
β- Endorphin

Supraspinal and spinal analgesia,

sedation
Constipation,
physical dependence

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14
Q

Receptor Endogenous Desirable Undesirable

OP3

A

OP3
(MOP/μ)

Enkephalin
β- Endorphin

Supraspinal and
spinal analgesia,

sedation
Respiratory depression, 
bradycardia, 
miosis, 
urinary retention, 
pruritis, 
nausea and vomiting, 
constipation,
physical dependence
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15
Q

Where is MOP

A

MOP is present
in para-aqueductal grey (PAG) of brain
and
descending inhibitory control pathway,

and mediates most of the
actions of opioids.

It augments descending inhibition
(reducing pain or
providing analgesia).

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16
Q

Receptor Endogenous Desirable Undesirable

OP4

A

OP4
(NOP)

Nociception

Nil

Anti-analgesia

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17
Q

Is the sigma receptor and Opioid receptor

A

The effects of sigma (σ) receptor are
not antagonised by naloxone,

and hence this receptor is
not classified as an
opioid receptor anymore.

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18
Q

Activation of opioid receptor
by an opioid molecule produces:

3 effects

A
  1. Hyperpolarisation by K+ efflux
  2. Inhibition of Ca+ influx,
    preventing neurotransmitter release
  3. Inhibition of adenylate cyclase
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19
Q

Site and action Effects Example

Presynaptic

A

Site and action

1 Inhibition of adenylate cyclase
(needed for Ca+ influx)

2 Inhibition of Ca+ influx

3 Facilitation of K+ efflux
(hyperpolarisation)

Effects
Failure of excitatory neurotransmitter
release (glutamate) at dorsal horn

Example
KOP and NOP:
prevent Ca+ influx

MOP, DOP: facilitate
K efflux

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20
Q

Site and action Effects Example

Post-synaptic

A

Post-synaptic

Facilitation of K+ efflux
(hyperpolarisation)

Failure of action potential generation

MOP, DOP: facilitate
K+ efflux

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21
Q

Opiate refers

A 
Opiate refers to only the alkaloids 
in opium and the 
natural and 
semisynthetic derivatives 
of opium.
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22
Q

The term opioid

A

The term ‘opioid’ includes all
naturally occurring or synthetic drugs

that have stereospecific actions at
opioid receptors,
the effects of which can
be antagonised by naloxone.

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23
Q

TABLE 2.11 Classification of opioids by synthesis

Endogenous

Natural

A

Endogenous Semi-synthetic Fully synthetic Opioid-like drugs

Endorphins
Enkephalin
Dynorphine
Nociception

Morphine
Codeine
Thebaine

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24
Q

Semi-synthetic

Fully synthetic

Opioid-like drugs

A

Semi-synthetic

Heroin
Hydromorphone
Hydrocodone
Oxymorphone
Oxycodone
Buprenorphine
Dextrometharphan

Fully synthetic

Pethidine
Fentanyl
Alfentanyl 
Remifentanyl
Sufentanil

Opioid-like drugs

Tramadol

25
Opioids by action @ receptor MOP agonist partial antagonist
MOP (μ) Agonist Morphine, pethidine, methadone, fentanyl, alfentanyl, remifentanyl sufentanil Partial agonist Buprenorphine ``` Antagonist Naloxone Naltrexone Pentazocine Nalorphine ```
26
Opioids by action @ receptor DOP agonist antagonist
DOP (δ) ag Morphine (μ > δ) Pentazocine Nalorphine antag Naloxone Naltrexone
27
What is tolerance context of opioids
Tolerance and dependence are induced by chronic exposure to opioids. Tolerance means that higher doses of opioids are required to produce the same effect, reducing the maximum response attainable.
28
what is responsible for tolerance
It is mainly due to | receptor desensitisation.
29
Does tolerance develop to adverse effects of opioids
Tolerance develops to most of the adverse effects as well, ``` like dysphoria, itching, urinary retention and respiratory depression, ```
30
does tolerance occur to adverse effects the same rate is there any side effects that do not display tolerance
but occurs more slowly to the analgesia and other physical side effects. However, tolerance does not develop to constipation or miosis.
31
How is analgesic efficacy determined
Analgesic efficacy is determined by calculating the ‘number needed to treat (NNT)’. NNT is defined as the average number of patients who need to be treated (with analgesic drug) to prevent one additional bad outcome (pain).
32
What is it the inverse of
It is defined as the inverse of the absolute risk reduction. NNT = 1 ________________________ (proportion of patients with at least 50% pain relief with analgesic – proportion of patients with at least 50% pain relief with placebo)
33
How can analgesics be compared
Various analgesics have been compared in the Oxford league table of analgesic efficacy. Codeine 60 mg is least efficacious, while selective COX-2 inhibitors are most efficacious.
34
Opioids and their metabolites Drug Morphine Enzyme system
Morphine UGT2B7 Morphine-6-glucuronide (10% but active) Morphine-3-glucuronide (80% but inactive)
35
Moprhine Active metabolite Actions
M6G: analgesia M3G: hyperalgesia
36
Opioids and their metabolites Drug Diamorphine Enzyme system Active metabolite Actions
Diamorphine Ester hydrolysis 6-Monoacetylmorphine (MAM) and morphine Morphine is active component
37
Opioids and their metabolites Drug Pethidine Enzyme system Active metabolite Actions
Pethidine CYP3A4 Norpethidine 50% analgesic action; neurotoxicity
38
Opioids and their metabolites Drug Codeine Enzyme system Active metabolite Actions
Codeine CYP2D6 Morphine, nor codeine Morphine: analgesia
39
Opioids and their metabolites Drug Tramadol Enzyme system Active metabolite Actions
Tramadol CYP2D6 O-desmethyltramadol (M1 metabolite) Analgesia
40
Inactive metabolite of fentanyl What is proparacetamol
norfentanyl is an inactive metabolite of fentanyl; propacetamol is a prodrug of paracetamol.
41
Conversion of Morphine PO into diff routes / drugs Take 10 pO IV morphine IM S/C S/C diamorphine Periop doses +-/
Route Ratio (as compared to oral morphine) Example Oral morphine 1 : 1 30 mg Intravenous morphine 1 : 3 10 mg Intramuscular morphine 1 : 2 15 mg Subcutaneous morphine 1 : 2 15 mg Subcutaneous diamorphine 1 : 4 (as diamorphine has two molecules of morphine) 7.5 mg Perioperative doses ± 20%
42
Epidural dose of Morphine Intrathecal Compared to PO dose
Epidural dose of morphine is 1 : 10 of oral (up to 5 mg), while intrathecal is 1 : 100 (100–200 mcg).
43
Morphine Important facts What type of pain is morphine very effective against vs what type less effective
Salient features of morphine are as follows. Particularly effective for visceral pain, while less effective for sharp pain.
44
How does morphine cause N+V where what receptors
Nausea and vomiting: stimulation of CTZ (5-HT3 and dopamine receptors).
45
Morphine What side effects of rapid release by what effect How is this reversed
Can cause histamine release if administered rapidly or in large doses, resulting in bronchospasm and hypotension; take naloxone.
46
Morphine When do patients experience more severe pruritis how is it mediated How is it treated What other meds can be used to Rx Is there anything noveau used
Pruritus when given intrathecally or epidurally. It is not histamine mediated treated with naloxone. Ondansetron, propofol and antihistaminics have been used. ``` Recent peripherally acting antagonists such as methylnaltrexone have been used to reverse peripheral side effects without reversing centrally mediated analgesia. ```
47
Morphine What effect can it have on the eye How is this mediated How is it reversed
Meiosis through stimulation of Edinger–Westphal nucleus; reversed by atropine.
48
Morphine How can it affect fluid balance
Can induce antidieresis by increasing antidiuretic hormone secretion, resulting in water retention and hyponatremia.
49
Morphine What affect can it have on ventilation How is this mediated
Chest wall rigidity mediated by interaction with dopaminergic and GABAergic pathways in substantia nigra and striatum. Difficulty in ventilation can result following administration of opioids at induction: take with muscle relaxants
50
PK PO How is morphine prepared How does this affect its absorption How does this affect onset Whats PO bioavail why
Morphine is a weak base, hence it is absorbed from the small bowel. This delays absorption and results in slow onset of oral dose. Oral bioavailability is 30% because of high first-pass metabolism in liver.
51
Morphine IV IM Bioavail Speed onset How is absorption S/C route Why
Intravenous and intramuscular bioavailability are higher and onset is faster (10 and 30 minutes, respectively). Because of low lipid solubility, its absorption from the subcutaneous route is slow and so is usually avoided.
52
Neuraxial morphine issues why
Neuraxial morphine is associated with rostral spread and delayed respiratory depression.
53
How is morphine metabolised To what What are their relative proportions
It is metabolised by UGT2B7 to active morphine-6-glucuronide (M6G) (10%–30%) and an inactive morphine-3-glucuronide (M3G) (70%– 90%).
54
What is the active metabolite of morphine What is its potency vs Morphine How is its PK differ What is an issue with the inactive metabolite
M6G is two to four times as potent as morphine, is more hydrophilic, stays in the brain for a longer period and undergoes enterohepatic circulation. M3G may be associated with morphine induced hyperalgesia
55
Morphine disposition in susceptible populations Age < 3 months Patient group Characteristic Effect and implication
Age < 3 months Reduced conjugation and renal excretion ability Prolonged duration, so be cautious; prefer shorter acting opioids (fentanyl > morphine)
56
Morphine disposition in susceptible populations Patient group Elderly Characteristic Effect and implication
Elderly Reduced Lean mass and hepatic blood flow Increased sensitivity Reduce doses
57
Morphine disposition in susceptible populations Patient group Characteristic Effect and implication High body mass index
High body mass index Lean body weight < total body weight Higher chances of obstructive sleep apnoea Calculate doses according to lean body weight Careful use of sedatives and opioids in view of obstructive sleep apnoea
58
Morphine disposition in susceptible populations Liver failure Patient group Characteristic Effect and implication
Liver failure Reduced metabolism and increased elimination half-life ``` Increased sensitivity (along with encephalopathy) ``` Cautious use in small titrated doses
59
Morphine disposition in susceptible populations Patient group Renal failure Characteristic Effect and implication
Renal failure Accumulation of M6G metabolite (renally excreted) Uraemic encephalopathy may increase sensitivity

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