Pharmacology Flashcards
What are the steps in the WHO analgesiac ladder?
- Paracetamol
- NSAIDs
- Weak Opiod (e.g. codeine, tramadol)
- Strong Opiod (e.g. morphine, oxycodone, heroin)
What is the difference between opiates and opioids?
Opiates- substance extracted from opium or of a similar structure to those in opium
Opioids- any agent (including endogenous peptides- endorphines/enkephalins) that act upon opioid receptors
What are some important brainstem regions involved in pain?
The periaqueductal grey (midbrain)
Locus ceruleus (pons)
Nucleus raphe magnus (medulla)
What is the role of the brainstem regions in regulating pain?
- The PAG is excited which produces analgesia. Either through electrical stimulation or by endogenous opioids or morphine.
- Activated PAG project into the NRM. This results in serotonergic and enkephalinergic neurones projecting into the dorsal horn, supressing the nociceptive transmission
- Morphine also excited the NRM neurones
- The LC is also excited. Noradrenergic neurones project into the dorsal horn, inhibiting transmission
How is opioid action mediated?
By G protein-coupled opiod receptors
What are the classifications of opioid receptors? (3)
- µ- responsible for most of the analgesiac action of opioids but also have some major adverse effects
- ð (delta)- contributes to analgesia but activation can be proconvulsant
- k (kappa)- contributes to analgesia at the spinal and peripheral level and activation associated with sedation, dysphoria and hallucinations
What are some side effects of opioids?
- Respiratory- apnoea
- CV- Orthostatic hypotension
- GI- Nausea, vomitting, constipation, increased intrabilliary pressure
- CNS- confusion, euphoria, dysphoria, hallucinations, dizziness, myoclonus, hyperalgesia (with excessive use)
How is morphine metabolised and excreeted?
Metabolised in the liver by glucuronidation
Excreeted by the kidney
How is morphine administered?
IV in high dependency areas or IM, SC, oral in general wards
In chronic pain, oral adminisatration is the most appropriate
Can be given by epidural and intrathecal routes by specialists
For what kind of pain is codeine given?
Its a naturally occuring opioid and is given in those with mild/moderate pain
How is codeine administered?
Orally
Why might codeine be a bad drug of choice in those with constipation?
It has additional anti-diarrhoeal and antitussive activity that may be useful in some cases but adverse causing constipation
What are some semi-synthetic derivitives of codeine with higher potencies?
Oxycodone and Hydrocodone
Through which routes can Fentanyl be given?
IV- to provide analgesia in mantience anesthesia
Also sutibal for transdermal and buccal delivery in chronic pain states (not in acute)
When might Pethidine be used?
In acute pain, particulalrly in labour
How is Pethidine administered in acute onset pain?
IV, IM or SC - rapid onset of action
Unsuitable in chronic pain as has a short duration of action
What is Buprenophine and when is it used?
A parital agonist
Useful in chronic pain with patient controlled injection systems (can also be given sublingually)
Slow onset but long duration of action
In which patients should Tramadol not be given?
Avoid in patients with epilepsy
When might Methadone be given?
Can be useful in treating patients with chronic pain in terminal cancer- given orally and has a long duration of action
Can also assist in withdrawl from strong opioids like heroin
When is Naloxone given?
To reverse opiod toxicity associated with a strong opioid overdose
Why might a newboen need Naloxone?
If a newborn is suffering from opioid toxicity as a result of administration of pethidine to the mother during labour
How do non-selsctive NSAIDs work?
They have analgesic, antipyretic and anti-inflammatory actions
Inhibit the synthesis and accumulation of prostaglandins by COX-1 and COX-2 enzymes
Why isn’t paracetamol classed as an NSAID?
It lacks anti-inflammatory activity and acts only centrally
Why might long term use of non-selective NSAIDs cause GI damage?
PGE2 produced by COX1 protects against the acid/pepsin environment
True or False?
Neuropathic pain responds well to ibuprofen
False
Neuropathic pain does not respond to NSAIDs and is relitively insensitive to opioids
In which conditions might you see neuropathic pain?
Trigeminal Neuralgia
Diabetic Neuropathy
Post-herpetic Neuralgia
Phantom limb pain
What drugs can be used to treat neuropathic pain?
Gabapentin and Pregabalin (anti-epileptics)
Amitryptyline, Nortryptiline, Desipramine (tricyclic anti-depressants)
Carbamazepine
