Opioids Flashcards
Opium
Natural extract of the poppy papaver somniferum. It contains morphine and other related compounds
Opioid
Any substance (natural or synthetic) that produces morphine like effects which are blocked by a morphine antagonist
Opiate
Normally occurring opioid
What is the ceiling effect?
Weak opioids: escalation of the dose typically causes side effects without improving analgesia
Strong opioids
- Morphine
- Oxycodone
- Diamorphine
- Fentanyl
- Pethidine
- Remifentanil
- Methadone
Weak opioids
- Codeine
- Dihydrocodeine
- loperamide (Imodium)
What is special about loperamide?
It is not an alagesic but is an agonist of the opioid receptors in the myenteric plexus so stops diarrhoea
Tramadol
Developed as an antidepressant but found to have analgesic actions
Pro convulsive drug so avoid in epilepsy
Naloxone
Primary antagonist of opioids
What administration is most common in post op care?
- IV (patient controlled)
* Intra muscular (avoid the sciatic nerve)
What administration is most common in palliative care (or for weak opioids)
- Oral
* Transdermal patch
What administration is most common for labour or big operations?
Catheter in the extradural space
What administration is most common for trauma
‘lollipop’ or lozenge
Explain oral bioavailability of opioids
- First pass metabolism
- Opioids are weak bases
- Unionised form is more diffusible
- Stomach is very acidic so is ionised
- Alkaline environment pushes drug into ionised states and it passes into the portal circulation and travels to the liver
What are the opioid receptors?
- Mu opioid peptide receptor (MOP) - majority acts here
- Kappa
- Delta
- Nociception
Where are the mu opioid receptors located?
Throughout the NS but especially at sites to do with pain: PAG; dorsal horn, thalamus, cortex, primary afferents
What are the endogenous opioids
- Enkephalins
- Endorphins
- Dynorphins
Describe the opioid receptors’ structure
- Protein
- Serpantine formation
- 7 transmembrane proteins coupled to G proteins
Describe the mechanism of opioid receptors
- closure of voltage sensitive calcium channels
- Opening of potassium channels: potassium moves from inside the cell to outside
- This hyper polarises the cell
- Inhibition of adenylate cyclase leading to reduced neurotransmitter release
What are the actions of opioids?
- Analgeisa
- Sedation
- Euphoria
- depresses respiration, antitussive effect
- histamine release
- Bradycardia
- Peripheral vasodilation
- Nausea, constipation
- Urticaria and itch
- Urinary retention
- Immune suppression
- Decreased ACTH, decreased prolactin, increased ADH
Describe the metabolism of opioids
- Mostly by cytochrome in the liver
* Many opioids have active metabolites that are excreted by the kidneys in the urine
Why should you be careful using opioids in those with renal impairment?
Active metabolites can build up
Cautions in extremes of age
- Neonates: liver enzyme sub optimal
* Elderly: smaller volume of distribution
What is an antagonist?
A drug with a high affinity for the receptor but no intrinsic activity
What is naloxone’s half life
Approx 45 minutes
Methadone
Used to manage addiction problems in the community
• Dries mouth
• Long half life
• Crave sweet foods
• Low first pass metabolism so high oral bioavailability
• Less sedating
