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Derm/Pain > Pain > Flashcards

Pain Flashcards

1
Q

What are the 4 proposed mechanism of action for paracetamol?

A

Paracetamol usually acts more centrally then peripherally

  1. COX inhibition but better adverse effect profile than other COX inhibitors
  2. Paracetamol metabolites activate TRPA1 receptors in the spinal cord- thermoreceptors that have an analgesic effect
  3. Paracetamol metabolite (AM404) activate enhance the endocannabinoid system- known as pain relievers though CB1 and TRPV1 receptors
  4. Activation of descending 5-HT pathways
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2
Q

What are 5 main effects of opioids?

A
  1. Analgesia
  2. Sedation
  3. Respiratory depression
  4. Cough supression
  5. Constipation
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3
Q

What are some adverse effects of opioids?

A 
Nausea and vomiting
Constipation
Dyspepsia
Drowsiness
Miosis
Dependence

Use with caution with patients with epilepsy, biliary colic, respiratory depression, hepatic impairment and in the eldery

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4
Q

MOA of morphine

A

Metabolite M6G is a strong against at MOR

Also actives MOR in PAG

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5
Q

MOA codeine

A

Usually found in combination with other analgesics

Prodrug that needs to be metabolised by CYP2D6 into morphine

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6
Q

MOA buprenorphine

A

MOR partial agonist but very affinity and slowly dissociates hence long duration of action (has an active metabolite as well)
KOR antagonist

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7
Q

MOA fentanyl

A

Strong MOR agonist (100x more potent than morphine)
High lipid solubility: Transdermal and buccal routes prefered
Long half life and released in a linear manner over 72 hours (reason to why patches are applied every 3 days)

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8
Q

When is the use of fentanyl contraindicated?

A

For short term analgesic use- cannot titrate small dose

Can cause serotonin syndrome (Increases 5-HT) - causation with MAOIs

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9
Q

What other opioid is hydromorphone similar to?

A

Morphine- MOR agonist

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10
Q

Beside being a MOR agonist, what other effects does methadone have?

A

NMDA receptor antagonist - role in the reduction of tolerance
Interacts with K channel in myocardium = prolong QT
Long half life (long acting metabolites)

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11
Q

Does oxycodone have against activity on all 3 opioid receptors?

A

Yes

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12
Q

Which receptors do pethidine act on?

A

MOR and KOR agonist

Short onset than morphine

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13
Q

Why is pethidine used in labour?

A

Analgesic effect without reducing the force of contractions

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14
Q

What are 3 precautions with pethidine?

A 
serotonin syndrome (it can weakly inhibit 5-HT reuptake) 
Toxic effects- convulsions and excitation
Metabolised into norpethidine - hallucinogenic and convulsant effects
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15
Q

MOA of tramadol

A
  1. Weak affinity MOR agonist- its metabolite has higher affinity (O-demethyltramadol)
  2. Inhibits NA and 5-HT reuptake - antidepressant effects since similarity to antidepressant drugs
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16
Q

What are some adverse effects of tramadol? (6)

A 
Nausea
Constipation
Dizziness
Autonomic nervous effects: dry mouth, perspiration, sweating 
Itch/ rash
17
Q

What are some adverse effect of aspirin?

A

GI effects- nausea, epigastric pain, ulceration with chronic use
Tinnitus
Rashes, bronchospasm
Reye’s syndrome

18
Q

What is the main MOA of diclofenac and what other 3 may contribute to its activity?

A
  1. non competitive inhibitor of COX 1 and COX 2
  2. Blocks arachidonic acid release and uptake
  3. Inhibit lipoxygenase enzymes
  4. Inhibit substance P
19
Q

Why does inhibition of COX 2 produce cardio side effects?

A

COX 2 inhibitors lower PGI2 and hence increase platelet activity (risk of arterial thrombosis)
Decreases the regulation of oxidant stress

PGI usually has cardioprotective effects- if blocked then can lea to risk of thrombosis, MI, PE, stroke

20
Q

Hepatic toxicity cause by paracetamol can be fatal- which metabolite causes this and who would you treat?

A

NAPQI
Treatment:
Induce vomiting to give gastric lavage
N-acetylcysteine (increases conjugating of reactive metabolite)
Methionine (increases conjugating of reactive metabolite)

21
Q

What are 2 examples of inhalation agents used for pain?

A

Nitrous oxide- widely used in anaesthesia

Methoxyflurane- used in ambulances

22
Q

How does capsaicin relieve pain?

A

Applied topically and acts on TRPV1
Causes pain due to release of substance P
But prolong exposure desensitises the nociceptive terminals and elevates pain threshold

23
Q

List 7 non drug treatments for pain

A
  1. Heat
  2. Ice
  3. Massage/ exercise/ relaxation techniques
  4. Cognitive behavioural therapies
  5. Surgery
  6. Accupuncture
  7. TENS
24
Q

List 5 locations where opioids can relieve pain

A
  1. Supraspinal
  2. Midbrain- PAG
  3. Brainstem- reticular formation and locus coeruleus
  4. Spinal- dorsal horn
  5. Peripheral- inflammatory cells, sensory afferent neurons

Cannabinoids also work in all these areas EXCEPT BRAINSTEM

25
Q

Which adenosine receptor has anti-nociceptive effects?

A

A1

Derm/Pain (5 decks)

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