Pharmacology of Analgesic Agents

Question 1

Analgesia (3)

Answer 1

Appropriate treatment of pain

Knowledge of patient’s concurrent analgesic medications for chronic pain

Recognition of adverse effects and avoidance of potential reactions

Question 2

Pain

Answer 2

Unpleasant sensory/emotional experience which we associate with tissue damage or describe in terms of tissue damage or both
Inadequate relief is a global concern
Not always cured and requires continuous medical management

Question 3

Pain sequence

Answer 3

Normal –> protective –> EITHER acute OR prolonged
ACUTE –> REFLEX
PROLONGED –> INFLAMMATION+REPAIR

Question 4

Congenital insensitivity to pain

Answer 4

SCN9A gene mutation in humans - loss of function due to Na channel mutations
Results in injury due to lack of pain

Question 5

Sources of pain

Answer 5

Injury e.g fractures

Disease e.g neuromyalgia

Question 6

Sensory pathway

Answer 6

Originates in PNS and travels to CNS (spinal cord and brain)
CNS transmits to cortex to create perception of pain

Question 7

Pain modulation

Answer 7

Emotion and attention affect nociception
Amount of pain does not relate to severity of tissue damage
Anxiety increases pain transmission
Complex cultural influences

Question 8

Dental pain results from (4)

Answer 8

Infection
Exposed nerve endings
Swelling in confined space
Fear

Question 9

NSAIDs and opioids are used to treat

Answer 9

Injury pain and chronic pain
By returning sensitivity to normal thresholds
Can be problematic

Question 10

Treatment of pain

Answer 10

Reduce tissue damage (NSAIDs, steroids, cooling)
Nerve block
Spinal cord (opioids)
CNS (opioids and psychological factors)

Question 11

Paracetamol 
When 
Mechanism
Type 
Route
Dose

Answer 11

Mild pain
N/A - inhibitor of prostaglandin synthesis
Analgesis, antipyretic
Oral, soluble, IV, rectal 
500mg-1g 4-6 hrly - max is 4g/24hrs

Question 12

Paracetamol - adverse effects

Answer 12

Uncommon
Hepatotoxicity - early treatment with N-acetyl-cysteine
Not contraindicated in liver disease

Question 13

NSAIDs e.g ibuprofen

Answer 13

IR inhibitor of COX1 +/ COX2
Inhibits inflammatory mediator synthesis
Effective at reducing acute inflammation

Question 14

NSAIDs side effects

Answer 14

GI tract - blood loss from minor mucosal breaches - peptic ulceration - indigestion
Renal function - reduction in intrarenal blood flow –> failure
Platelets - COX inhibition, bleeding tendency
Cardiovascular - fluid retention due to renal failure –> heart failure
Respiratory - some aspirin sensitive asthmatics

Question 15

Newer NSAIDs

Newer COX2 inhibitors

Answer 15

Ibuprofen, diclofenac, naproxen
Less bleeding as side effect if only COX2 affected as GI tract and platelets mainly associated with COX1
Not nephrotoxic

Question 16

COX2 and CV

Answer 16

Absence of anti platelet effects
Prothrombotic
Increased risk of MI and stroke

Question 17

NSAIDS and elective surgery

Answer 17

Stop 5 days prior to surgery
Reduces risk of bleeding
Consider platelet transfusion

Question 18

Weak opioids - mod -severe pain

Answer 18

Codeine
Dihydrocodeine
Both metabolised to morphine
Some people have minimal enzyme

Question 19

Cardiovascular effect of weak opioids

Answer 19

Reduced simp outflow, increased vagal tone
Bradycardia
Hypotension

Question 20

Respiratory effect of weak opioids

Answer 20

Inhibit cough reflex

Respiratory depression

Question 21

GI effect of weak opioids

Answer 21

Reduced gastric motility
Constipation
Nausea
Vomiting

Question 22

CNS opioid effects

Answer 22

Sedation, euphoria, dysphoria, excitation

Question 23

Analgesia for CNS

Answer 23

Spinal cord - reduced pain fibre transmission
Brainstem - reduced pain projection to higher centres
Respiratory depression, reduced brainstem response to hypoxia and hypercarbia

Question 24

Weak opioid/paracetamol combinations

Answer 24

Co-codamol e.g

Less popular

Question 25

Adjuvant therapies

Answer 25

Co-analgesics - other drugs, blocks, surgery, Rtherapy, addressing psychosocial issues

Question 26

Pain management (3)

Answer 26

Assessing severity in context of daily living and functioning Acute pain - large variation in requirements Amount of analgesia required is enough to stop the pain

Question 27

Anaphylaxis

Answer 27

Severe reaction to medication

Question 28

Reversal of opioid effects

Answer 28

Naloxone 400mcg

Question 29

Opioid dependency Chronic use Acute withdrawal symptoms if stopped suddenly

Answer 29

Reduced effect as the CNS improves tolerance therefore dosage increases Hypertension, sweating, tachycardia, diarrhoea, anxiety, hallucinations

Question 30

New opioids As effective as Effects

Answer 30

Nefopam, Tramadol Codeine, less constipation Nausea, dizziness, sweating

Question 31

Adverse effects: Tramadol Overdose causes? New legislation?

Answer 31

Increased no. fatalities due to overdose Dependency due to long term use Controlled drug

Question 32

Paracetamol combos

Answer 32

Co-codamol/proxamol

Question 33

Cautions in prescribing opioids

Answer 33

Consider hepatic metabolism and renal excretion Prolonged effect on liver and kidneys Respiratory disease, sleep apnoea, increased sensitivity

Question 34

Severe pain

Answer 34

Fentanyl patch | Morphine (oral dose 3x IV dose)

Question 35

Post operative analgesia

Answer 35

IV morphine | Patient controlled

Question 36

Route of administration

Answer 36

``` Oral IV Rectal Epidural Buccal Intrathecal i.m/s.c transdermal ```

Question 37

Chronic pain

Answer 37

Oral morphine syrup/tabs Transdermal patch S.C morphine

Question 38

Alternatives x2 For? Adverse effects?

Answer 38

``` Gabapentin Pregabalin Neurogenic pain Reduce CNS transmission Dizziness, nausea, sedation, dizziness ```

Question 39

Antidepressants

Answer 39

Amitryptilline Duloxetine Citalopram

Question 40

What are enkephalins?

Answer 40

Enkephalin are the bodies own produced opioids. (endogenous opioids)

Question 41

How do enkephalins work? Substance P What chemical increases substance P release for

Answer 41

Enkephalins inhibit pain by stimulating the kappa opioid receptors. Pain stimulating NT Kappa opioid receptor inhibits substance P release. Opioids also work on the higher centres – brainstem. NMDA – NT that increases substance P release. N-methyl-D-aspartate is released in anxiety --> pain