Drugs Used In The Management Of Pain

Question 1

What is pain?

Answer 1

Pain is a complex subjective sensation reflecting real or potential tissue damage and the effective response to it. It is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage

Question 2

How do drugs modulate pain neural pathways in order to bring about analgesic action?

Answer 2

Drugs that have analgesic actions act by modulating the pain neural pathways in various ways that include:
• Inhibition of activity at nociceptors
• Inhibition of synthesis of mediators of nociception and pain transmission
• Inhibition of transmission of pain signals
• Potentiation of mediators that inhibit transmission of pain signals

Question 3

Outline the pain neural pathway

Answer 3

Noxious stimuli are detected by receptors in pain sensitive tissues (nociceptors).
Signals are transmitted by sensory fibres to the dorsal horn of the spinal cord.
Signals are transmitted via ascending spinal pathways to various parts of the brain.
Signals that are received in the thalamic nuclei, periventricular grey matter and brain stem reticular formation are processed and passed on to the sensory cortex giving one the sensation of pain

Question 4

Which substances mediate the detection of noxious stimuli by nociceptors?

Answer 4

prostaglandins,
leukotrienes,
5-HT,
histamine,
bradykinin and
substance P

Question 5

Which substances mediate the transmission of signals via sensory fibers to the dorsal horn of the spinal cord?

Answer 5

Substance P
Glutamate

Question 6

Which substances mediate the transmission of signals via the ascending spinal pathways?

Answer 6

neuropeptides (substance P and calcitonin gene-related peptide) and nitric oxide

Question 7

Which substances mediate the receival of signals in several sites, such as the reticular formation and medulla?

Answer 7

Enkephalins and endorphins,
noradrenaline and serotonin

Question 8

Which drugs inhibit the generation of mediators of pain?

Answer 8

1. NSAIDs — inhibit the synthesis of prostaglandins
2. Glucocorticoids — inhibit the synthesis of prostaglandins and leukotrienes

Question 9

Which drugs inhibit the initiation and propagation of action potentials?

Answer 9

1. Local anesthetics — block sodium channels and thereby block the conduction of action potentials along sensory nerves
2. Ketamine — blocks the action of glutamate on NMDA receptors

Question 10

Which drugs inhibit neurotransmission in the ascending, spinal pathways?

Answer 10

General anesthetics specifically inhalational and some intravenous general anesthetics

Question 11

Which drugs potentiate inhibitory mediators in the descending inhibitory pathways?

Answer 11

1. Opioid analgesics — mimic enkephalins and endorphins, opioid peptides that are released in the body in response to pain
2. tricyclic antidepressants and tramadol — enhance noradrenaline and serotonin transmission by inhibiting their reuptake