Drugs Used In The Treatment Of Pain (Adjuvants)

Question 1

Describe the ascending pain pathway

Answer 1

• A-delta fibers are myelinated (insulated with a myelin sheath). The pain is fast and well localized, like the initial prick or stinging sensation following an injury.
• C fibers are nonmyelinated and smaller than A-delta fibers. They transmit pain much slower. The pain is more lasting, generalized and described as a dull ache
• After afferent A-delta (myelinated and fast) and C-fibers (unmyelinated and slow)
  synapse with the interneurons.
• These cross over to the contralateral side and ascend primarily via the spinothalamic tracts to the thalmus and cortex

Question 2

What are adjuvant analgesics?

Answer 2

Adjuvant analgesics are drugs that have primary indications other than pain but are useful in pain relief in the management of certain pain conditions
They are useful in pain conditions such as cancer infiltration pain, neuropathic pain, pain associated with inflammation and headache syndromes

Question 3

Describe the MoA of tricyclic antidepressants as adjuvant analgesics

Answer 3

Increase noradrenaline and 5-HT in the inhibitory descending pathways (inhibit re-uptake of noradrenaline and 5-HT)

Question 4

What are the indications of TCA as adjuvant analgesics?

Answer 4

Used in the management of headache syndromes (e.g. migraine), facial pain, low back pain, denervation pain and neuropathic pain

Question 5

Which TCAs are used as adjuvant analgesics?

Answer 5

amitriptyline

Question 6

Which corticosteroids are used s adjuvant analgesics?

Answer 6

Dexamethasone and prednisolone

Question 7

What is the MoA of corticosteroids used as adjuvant analgesics?

Answer 7

Inhibits synthesis of prostaglandins and leukotrienes

Question 8

What are the indications of corticosteroids as adjuvant analgesics?

Answer 8

Used in the management of pain due to inflammatory diseases, tumour infiltration of nerves, increased intracranial pressure, severe bone pain, and rheumatoid arthritis)

Question 9

What is the MoA of ketamine as an adjuvant analgesic?

Answer 9

Blocks glutamate receptors (blocks the glutamate-activated NMDA receptor calcium channel) in the dorsal horn and activates opioid receptors-(N-methyl-D-aspartate receptor).

Question 10

What are the limitations of ketamine?

Answer 10

Usefulness is limited by psychotropic effects (can be reduced by simultaneous administration of benzodiazepines and anti-psychotics)

Question 11

Which drug classes do clonidine and mexiletine belong to?

Answer 11

Clonidine - Alpha2 adrenoceptor agonist
Mexiletine - Sodium channel blocker

Question 12

What is the action and indication of clonidine as an adjuvant analgesic?

Answer 12

Inhibits nociceptive transmission in the spinal cord
Used in migraine prophylaxis

Question 13

What is the indication of mexiletine as an adjuvant analgesic?

Answer 13

Used in the management of neuropathic pain, migraine, and cancer infiltration pain