Analgesics

Question 1

Explain the pain pathways

Answer 1

1. When trauma occurs at a peripheral site, peripheral nerves are stimulated
2. An action potential is created transmitting information about tissue damage along the nerve to dorsal root ganglion
3. This synapses with second order neuron in spinal cord
4. The spinal crosses over the spinal cord and travels upward rising through the medulla, though the periaqueductal are of the mid brain and synapses with a third order neuron within the thalamus
5. This third order neuron then continues on ending at the primary somatosensory area of the cerebral cortex

Question 2

Describe the different analgesic drug groups and the mechanisms of action

Answer 2

1. NSAIDS (paracetamol)
   - inhibit enzyme COX
   - converts arachidonic to endoperoxides
   - inhibits prostaglandin synthesis
2. Opioids (codeine)
   - have G-protein receptors linked to inhibition of adenylate cyclase
   - inhibits opening of calcium channels
   = less pain conducting neurotransmitters released

Question 3

Outline how opioid analgesic side effects can be managed

Answer 3

Short term
1. Sedation – naloxone
2. Respiratory suppression – give naloxone quickly
3. Nausea and vomiting – antiemetic before

Long term
1. Addiction
2. constipation – lactulose
3. Tolerance dependance

Question 4

Describe the options available for pain relief and rationale for prescribing

Answer 4

• Antidepressants
• Gabapentinoidse