PHARM Y1 S2: Opioids

Question 1

why is fast pain more readily localised than slow pain?

Answer 1

• fast = all afferent fibres reach the thalamus and somatosensory cortex
• slow = many fibres end in lower brain regions so can’t determine a specific location

Question 2

what are the 3 main receptors for opioids?

Answer 2

• mu receptor (main one)
• kappa and delta also exist

Question 3

MOA of opioids (ascending + descending)

Answer 3

• most are agonists at mu receptors
• ascending: spinothalamic tract
• descending: corticospinal tract, activates periaqueductal grey (PAG) in brain
• presynaptic: inhibits Ca2+ influx > decreased NT release
• postsynaptic: mimics endogenous enkephalins by causing K+ efflux > hyperpolarisation
• therefore inhibits nociceptive transmission

Question 4

what is morphine used for?

Answer 4

• severe, long-term pain

Question 5

what is codeine used for?
- what are some features of it?

Answer 5

• pain and coughs
• 1/5 potency of morphine but more reliably absorbed and rarely addictive
• should not be given to kids under 18, prescription only

Question 6

what is oxycodone used for

Answer 6

• chronic and severe pain
• similar to morphine

Question 7

what is fentanyl used for

Answer 7

• moderate to severe pain (short-term)
• breakthrough pain e.g. cancer

Question 8

naloxone: MOA and use

Answer 8

• ANTAGONIST at mu receptor
• can induce hyperalgesia if the Pt is already in pain b/c inhibits endogenous opioids
• indication: temporary Tx of opioid overdose

Question 9

side effects of opioids

Answer 9

• euphoria or dysphoria
• sedation
• inhibition of GIT thru blocking ACh release > constipation
• N&V
• itching (histamine)
• cardiovascular/respiratory depression
• bronchoconstriction
• hypotension

Question 10

loperamide MOA, use, AEs

Answer 10

• agonist @ mu receptors
• poorly absorbed, stays in GIT = only acts on mu receptors in bowels = decreased peristalsis = anti-diarrhoeal
• no analgesic effect b/c poor absorption means it never gets to spinal cord so can’t act on afferent neurons
• AE: constipation

Question 11

order the potencies of opioids

Answer 11

• loperamide (basically none)
• codeine
• morphine
• oxycodone
• heroin
• fentanyl (v. high)

Question 12

what are enkephalins and what is their function

Answer 12

• small peptides released from interneurons as part of the descending pathway - endogenous opioids
• function: pain modulation, released w/ high impact exercise

Question 13

3 phases of nociception

Answer 13

• transduction of noxious stimulus into a nerve signal
• transmission of impulses to spinal cord, brain stem, thalamus, somatosensory cortex
• perception: Pt becomes conscious to pain

Question 14

tramadol (atypical analgesic)

Answer 14

• acts on mu opioid receptors
• increases levels of NA and 5-HT (serotonin) > inhibits nociceptive transmission @ dorsal horn
• less respiratory depression and dependence
• adverse effects: N&V

Question 15

what is fibromyalgia?

Answer 15

• chronic musculoskeletal pain, fatigue, insomnia (unknown cause)
• can use opioids which raise NA and 5-HT in CNS to bring some relief but not effective long term

Question 16

gabapentin

Answer 16

• inhibits Ca2+ channels to decrease release of excitatory NTs in CNS
• reduces central sensitisation of post-op pain

Question 17

what drugs can be used for neuropathic pain

Answer 17

• clonidine
• ketamine

Question 18

transcutaneous electrical stimulation (TENS)

Answer 18

• triggers release of endorphins and enkephalins
• increases other sensory afferents e.g. touch, pressure to ‘close the gate’ for painful stimuli

Question 19

which tract transmits pain

Answer 19

• lateral spinothalamic

Question 20

analgesic ladder

Answer 20

• 1. non-opioid e.g. NSAIDs + panadol
• 2. weak opioids e.g. tramadol, codeine
• 3. strong opioids e.g. morphine, oxycodone, fentanyl