Opioids Flashcards
Name an analgesic for each stage in the WHO ladder:
Simple analgesia
Weak opioid
Strong opioid
Paracetamol, NSAID
Codeine
Morphine, fentanyl, oxycodone, alfentanil, methadone
Why are NSAIDs preferred over opioids in arthritis?
NSAIDs work better,
Tackle inflammation
To which two drug classes does neuropathic pain (e.g. diabetic neuropathy) respond well?
Antidepressants
Anticonvulsants
Describe the administration options of morphine
Basically all:
IM, IV, SC, PR, PO (syrup)
H/e gut absorption is unpredictable and morphine has high first pass metabolism
Decribe the distribution of morphine in relation to tissues, placenta and BBB
All tissues
Crosses the placenta and acts on the foetus (bab may be born with resp depression and withdrawl sx)
Struggles to cross the BBB therefore pts don’t get much of a high
How is morphine metabolised, and what effect do the metabolites have?
Glucuronidation in the liver
M3G - can cross the BBB and irritate the brain (morphine 3rd gen - pretty shit)
M6G - analgesic effect (morphine 6th gen - good shit)
How is morphine eliminated?
Renal elimination
What is the MoA of morphine?
Complete activation of u receptors
Minimal effect on K and delta
When is fentanyl used?
- Surgery setting
- Patient-controlled analgesia machines
Name three ways fentanyl can be administered
IV
Epidural
PO
What is the metabolism and elimination of fentanyl?
Metabolised in the liver by CYP3A4
Eliminated by the kidneys, but less so than morphine so can be used in ore renally impaired pts
How do the affinity and intrinsic activity of fentanyl compare to morphine?
Higher therefore fentanyl is more potent
State three side effects of morphine and fentanyl
- Resp depression (reduces responsiveness of the medullary resp centre to CO2)
- Emesis (stimulates CTZ)
- Constipation and nausea
- Asthma attacks in asthmatics (mast cell degranulation, more so in morphine)
- Miosis
- Drowsiness and dizziness
What are the two methods of administration of codeine?
PO
SC
How is codeine metabolised, and how does this vary between individuals?
Liver
Codeine -> morphine by CY2D6
Some people express this more, so get lots of morphine and side effects
Some people express this less therefore codeine doesn’t work
Inhibited by fluoxetine
How does the potency of codeine compare to morphine?
Not as potent, therefore used more for mild to moderate pain and as a cough depressant
State two side effects of codeine
Constipation (give laxative if using long term)
Resp depression (worse in children bc of larger adenoids and tonsils which can obstruct airways)
State three uses for buprenorphine
Chronic pain
Palliative care (admin options, and less likely to have falls)
Opioid addiction treatment
State tw administration options of buprenorphine
- Transdermal (patch on the skin, lasts for a week)
- Buccal
- Sublingual
Describe the metabolism of buprenorphine
Half life of 37hrs
Liver
By CYP3A4, then glucuronidation
How is buprenorphine eliminated?
Billiary excretion
Therefore safe in renally impaired
Compare the affinity and action of buprenorphine
Very high affinity for the u receptor partial agonist (low intrinsic activity) therefore fewer side effects and less activation of receptors
State three administration options of naloxone
IV, IM, intranasal
PO has a 2% bioavailability so not rly used
What is naloxone used for?
Competitive antagonist of u receptors, so used to treat opioid overdose
Can give people close to known addics nasal naloxone, so if the pt overdoses, friend can give naloxone before ambulance arrives
Has a short half-life (30-60mins) so give as slow infusion so you don’t crash from the overdose again
