Opioid analgesics and pain processing Flashcards
What blocks the effect of morphine
Naloxone
Where do opioids act
- mew
- delta
- kappa
receptors
What do the opioid receptors do
Inhibit adenylate cyclase and reduce cAMP
Alter ion channels through G protein coupling to channels
- open K+ channels
- close Ca2+ channels
What is the effect of opioids on neuronal transmission
1 opioid receptor agonist binds to presynaptic neuron
2 This increases Gi which decreases AC and CAMP.
3 This then decreases protein kinase
4 Calcium channels are blocked and increases K+ efflux when an action potential arrives, ca2+ can’t get in and K+ leaves.
5 Neuron becomes hyper polarised
6 Postsynaptic neuron has decreased excitability and transmission. It is also hyper polarised
Where does morphine act
mew receptor
What is an important side effect of morphine
Constipation
Where sites of action of opioids
PAG
NRM
How do opioids act at PAG and NRM
Morphine binds to receptors on PAG and NRM
Greater excitation of them both
Greater release of inhibitory substances to spinal cord so less pain
Clinical issues of opioids
Tolerance. Higher plasma concentration to achieve same pharmacological effect
are opioids used for nerve damage
Work for hyperalgesia but not allodynia
Can opioid reduce acute pain and why
Yes
Opioid receptors are present on C fibres
Can opioid reduce tissue damage (chronic pain) and why
Yes
opioid receptors found on c fibres
If patient doesn’t respond to opioids what do you do
change drug or route: Switch to subcutaneous or epidural morphine
spinal opioid: epidural/intrathecal give little benefit over subcutaneous. good for combination therapy
-Infusion for chronic pains
