Analgesics: Opioids Flashcards
What are analgesics?
Analgesics are drugs which act to relieve pain.
In general, how do analgesics work?
They act in various ways on the peripheral and central nervous system.
How do we know which to use?
Depends on type of pain.
What are opioids?
Synthetic opioids are the main class of analgesic used in the clinical treatment of moderate to severe pains to produce a morphine-like effect. They are highly effective (except in some cases of neuropathic pain).
How do opioids work?
They mimic endogenous opioids so act as agonists on one of four opioid receptors found in the brain, spinal cord and peripheral nervous system.
What are the opioid receptors?
A group of inhibitory GPCRs with opioids as ligands.
What are the types of opioid receptors and where are they found?
There are 4 types throughout P and CNS. On post-synaptic sites:
- Mu
- Delta
- Kappa
- Orl1
Give examples of synthetic opioids
Moprhine, codeine, fentanyl, pethidin, pentazocine etc.
How does this result in analgesia?
Interaction of opioid with central receptor causing hyperpolarisation and inhibition of NT release. Analgesia can be limited by side effects caused by interactions with peripheral and some central.
Discuss spinal opioid analgesia.
Opioid receptors in spinal cord are predominantly mu/delta found in substanta gelatinosa of superficial dorsal horn which is where C fibres end.
Use epidural routes.
Opening of K+ channels, Ca2+ influx, decrease release of transmitters from C fibres. Remaining receptors hyperpolarise neurons resulting in further inhibition of C fibres.
Discuss supraspinal analgesia
This is another important site for opioid action but the mechanism here is poorly understood.
Located in 5HT and noradrenergic nuclei of brain stem and midbrain. Triggered by painful inputs and lead to psychological aspects of pain. Activation of mu/delta/kapp receptors alter level of activity in descending pathways from these areas of the spinal cord.
