18) Opioid Analgesics Flashcards
What is the pain pathway?
Nociceptor -> dorsal root -> thalamus -> primary sensory cortex
Where are endogenous opioids found?
Limbic system, thalamus, spinal cord, primary afferent peripheral terminals
What are the 3 major groups of endogenous opioids?
Enkephalins
Endorphins
Dynorphins
Describe the opioid receptors:
GPCR and 3 types:
mu opioid receptor (u) - main effects
delta opioid receptor (d)
kappa opioid receptor (K)
What is the effect of opioids binding at the opioid receptors?
Outward flux of K+, decreased excitability
Decreased influx of Ca2+ = reduced neurotransmitter release
Decreased cAMP synthesis
What are some ADRs of opioids?
N&V, constipation, drowsiness, mioisis, confusion
Resp depression
Hypotension
Describe and give examples of full agonists at opioid receptors:
Morphine, codeine and methadone
Have high affinity for u receptor
Give an example of a partial agonist at opioid receptors:
Buprenorphine
Describe and give examples of mixed agonist/anatagonists at opioid receptors:
Nalbuphine - antagonist at u, partial agonist at K, weak agonist at d
What is the benefit of mixed agonist/antagonists at the opioid receptor?
Analgesia without euphoria
Give an example of a full antagonist at the opioid receptor and its use:
Nalaxone - reverse effects of fatal agonists e.g. resp depression
Describe the pharmacokinetics of morphine:
Low bioavaliability due to first pass metabolism
Half life 2-6hrs
Why is methadone more suited for chronic pain management?
Long half life due to high oral bioavaliability and high protein bindng
How is morphine metabolised?
Glucoronidation
What are the main clinical uses of opioids?
Analgesic - moderate to severe pain, particularly of visceral origin
