8. Pharmacology of pain

Question 1

What is nociceptive pain?

Answer 1

This is acute pain, leading to a linear response in the brain i.e. a high intensity stimuli will result in a greater level of pain

Question 2

What is neuropathic pain?

Define neuropathic pain

Answer 2

This is chronic pain - an abnormal pain which offers no protective function - chronic maladaptive plasticity in a negative aspect
This often occurs following a traumatic injury

Pain arising as a direct consequence of lesion or disease affecting the somatosensory system

Question 3

Which factors can influence the perception of pain?

Answer 3

Cognition - attention, distraction, control
Mood - depression, anxiety
Contexts - beliefs, expectations, placebo
Chemical and structural - atrophy
Injury - peripheral, central sensitisation
Genetics

Question 4

What are opioids and why are they important?

Answer 4

These are substances that act on opioid receptors to produce morphine-like effects and are used medically to relieve pain

These remain the most important component for the treatment of pain

Question 5

What type of receptors are opioid receptors and where are they located?

What are the different types of opioid receptors?

Answer 5

They are g-protein coupled receptors
Opioid receptors are located throughout the body - widespread distribution explains the broad spectrum of effects induced by opioid agonists

Mu receptors
Delta receptors
Kappa receptors

Question 6

Give the mechanism of action of morphine

Answer 6

Morphine will bind to the opioid receptor to trigger a host of intracellular events:
Activation of potassium conductance and decreased calcium conductance
SO the neurones become hyperpolariesd and less excitable and there is a reduction in the release of neurotransmitters

Question 7

What factors should be considered when choosing an opioid drug?

Answer 7

Drug pharmacokinetics
Drug pharmacodynamics
Individual patient factors
Supply/availability of the drug 
Possible/desirable routes of administration

Question 8

Name some common opioid drugs (NEED TO KNOW THESE)

Answer 8

Morphine
Heroin
Dextromoramide
Methadone

Question 9

What is meant by personalised analgesia?

Answer 9

This is patient-controlled analgesia (PCA) i.e. prescribing the quantity of analgesia as is needed - due to genetic patient variability

Question 10

What is meant by opioid switch?

Answer 10

This is switching from one opioid drug to another when a patient becomes tolerant to one particular drug

Question 11

What is the analgesic ladder and give the stages?

Answer 11

This is a pain ladder which provides a guideline for the use of drugs in the management of pain

1 - non-opioids and adjuvant drugs
2- moderate efficacy opioids, non-opioids and adjuvant drugs
3 - high efficacy opioids, non-opioids and adjuvant drugs

Question 12

What non-opioid drugs are available for analgesia?

Answer 12

Paracetamol
NSAIDs
Anticonvulsant drugs
Tricyclic antidepressants

Question 13

How does Paracetamol work?

Answer 13

Reduces the active oxidised form of COX-2
Analgesic and antipyretic

NB. Little anti-inflammatory effect

Question 14

How do NSAIDs work?

Name the common ones

Answer 14

Inhibition of COX enzymes e.g. COX-1 and COX2

Aspirin - analgesic, antipyretic and anti-inflammatory
Ibuprofen, diclofenac - analgesic and anti-inflammatory

Question 15

What are COX enzymes?

Answer 15

These are enzymes which produce prostaglandins
Prostaglandins promote inflammation, pain and fever

COX1 and COX2

COX1 also activates platelets and protects the stomach and intestinal lining

Question 16

What are the common indications and side effects of NSAIDs?

Answer 16

Nausea, GI bleeding

Rheumatoid arthritis, osteoarthritis, gout, muscle spasm

Question 17

Define local anaesthetic and give the name of some common ones

Answer 17

Technique to induce the absence of sensation in a restricted region of the body i.e. local insensitivity to pain

E.g. lignocaine, bupivacaine, prilocaine

Question 18

What is the mechanism of action of local anaesthetics?

Answer 18

Blockage of sodium channels

Question 19

Define general anaesthetic and give the name of some common ones

Answer 19

The induction of a state of unconsciousness with the absence of pain sensation over the entire body

Nitrous oxide
Xenon

Propofol
Etomidate
Ketamine

Question 20

What is the mechanism of action of general anaesthetics?

Answer 20

Activation of inhibitory receptors or inhibition of excitatory receptors

Question 21

What are the different ways in which general anaesthetics can be administered?

Answer 21

Inhalation or intravenous

Question 22

What is trigeminal neuralgia and what is it’s cause?

Answer 22

This is the most common facial pain syndrome - involving one or more of the branches of the trigeminal nerve

Due to compression, distortion or stretching of the trigeminal nerve root fibres - generally by a branch of the anterior or posterior inferior cerebellar artery

Question 23

How does trigeminal neuralgia present?

Answer 23

Presents as sudden, paroxysmal attacks of pain: electric shock-like, sharp, stabbing, commonly unilateral
Lasts from a few seconds to a few minutes

Question 24

What is the treatment for trigeminal neuralgia?

Answer 24

The treatment for this is pharmacological medication:
Carbamazepine
Baclofen
Phenytoin
Valproate