Analgesics Flashcards
What 3 reasons can be pain be useful for?
Warning individual there is a problem
Assisting clinician in localising pain
May help with diagnosis
What is a common and distressing symptom of many illnesses and diseases?
Pain
What uses a receptor to detect it and also needs pathways to the brain to inform the patient that there is a stimulus causing it?
Pain
What are nociceptors?
Receptors that detect pain
What are receptors that detect pain called?
Nociceptors
Do nociceptors have high or low thresholds?
Why?
High - so only detect stimulus that is potentially tissue damaging
What 3 types of damage do nociceptors detect?
Mechanical
Thermal
Chemical
What are the 3 sensory afferents?
AO Fibres
C Fibres
AB Fibres
What type of damage do AO Fibres detect?
Mechanical, thermal and chemical
What type of damage do C fibres detect?
Mechanical, thermal and chemical
Which fibres detect pressure, touch and position?
AB fibres
Which fibre detects sharp, well-localised pain?
AO fibres
Which fibre detects dull pain?
C fibres
What happens to AO and C fibre pathways when the AB pathway is stimulated?
It can marginally interfere with the others - modulating pain
What is the gate control theory of pain?
Rubbing an area - this stimulates the AB pathway and modulates pain caused by the other two pathways
What is the thickest/biggest and fastest sensory afferent pathway?
Which is the slowest and smallest?
AB is fastest (touch) Then AO (sharp localised pain) Then C (dull pain)
Which sensory afferent pathways are myelinated?
AO and AB
How does the pain/touch stimulus reach the sensory cortex?
It goes to the dorsal horn, spinothalamic tract, ventral posterior lateral nucleus (thalamus) then the sensory cortex
Horn-Tract-Thalamus-Sensory Cortex
What are the main 4 things that activate action potentials and cause inflammation, as a response to pain?
B5PH
Bradykinin
5-HT
Prostaglandins
Histamine
What do nociceptors release to cause inflammation, that act on the mast cells to produces histamine and blood vessels to produce oedema?
CGRP
Substance P
What would reducing the production of Bradykinin, 5-HT, Prostaglandins and Histamine do?
Prevent/reduce inflammation
What is the main part of the inflammatory ‘soup’ that we need to inhibit in order to stop the action of other mediators?
Prostaglandins
What sensitises afferent C fibres to bradykinin?
Prostaglandins
What drugs inhibit prostaglandin production?
NSAIDs
Non-Steroidal Anti-Inflammatory Drugs
What do NSAIDs need to inhibit in order to inhibit the production of prostaglandins?
COX 1 and COX 2 - as they are needed to produce them
Which COX enzyme is responsible for pain and inflammation?
COX2
What are the 4 pharmacological reactions of NSAIDs?
Antipyretic
Analgesic
Anti-inflammatory
Musculoskeletal Pain
What drugs can be used as antipyretic, analgesics, anti-inflammatory and to combat musculoskeletal pain?
NSAIDs
What does antipyretic mean?
To reduce body temperature during fever
What is the name for when a drug reduces body temperature during fever?
Antipyretic
When we say a drug provides the relief of pain associated with the increased production of PGs (such as arthritic, muscular, dental pain etc) what do we say it is?
An analgesic
What are arthritic, muscular, dental pain, post-partum and bone cancer pain examples of?
What treats it?
Pain produced by increased prostaglandins.
NSAIDs can act as an analgesic for this
When a drug reduces oedema and the sensitisation of nociceptors, what do we call this and what drug can do this?
Anti-inflammatory
NSAIDs
What is chronic treatment?
An increased dosage of drug or prolonged treatment
What are the side effects of NSAIDs if they are used as a chronic treatment?
(e.g. for chronic arthritis)
DINVUG
Indigestion, diarrhoea, nausea, vomiting, gastric bleeding and ulceration
What area do the negative side effects of NSAIDs tend to affect?
The GI Tract
Explain how long-term NSAID use can cause GI tract side effects:
NSAIDs inhibit COX 1, which synthesises certain prostaglandins (PGI2 and PGE2) that are important for mucus and HCO3/bicarbonate secretion - these help decrease acid secretion and increase blood flow to the stomach to protect it.
Inhibiting COX1 stops this protection = ulcers etc
NSAIDs bind to COX 1 and COX 2 - what are the results of this?
COX 2 = reduces pain and inflammation - good
COX1 = reduces mucus and bicarbonate secretion = more acid and less blood flow in stomach - bad? GI side effects
What are celecoxib and etoricoxib?
Pay attention to COX in name.
What is good about them?
They are NSAIDs that only inhibit the COX2 enzyme - reducing side effects.
Can cause MI however.
Most NSAIDs inhibit both the COX 1 and 2 Enzyme.
What 3 ways can reduce the negative side effects of this?
E P P
Enteric Coating of Tablets (protects stomach lining from effects)
Protective Agent - give with another drug: Misoprostol (prostaglandin analogue) or Omeprazole (Proton Pump Inhibitor)
Pro-Drugs - must be metabolised before it works
e.g. sulindac, nabumetone, fenbufen
Why would you give misoprostol with NSAIDs?
To act as a protective agent as it is a PGE1 analogue
Why would you give Omeprazole with NSAIDs?
It is a proton pump inhibitor and acts as a protector against the side effects
Name 2 drugs that can act as a protective agent with NSAIDs
Misoprostol and Omeprazole
Why does an enteric-coating on NSAIDs reduce side effects?
It protects the stomach lining from the tablets effects
Why do pro-drugs reduce NSAID side effects?
They have to be metabolised in the liver before they become active, reducing the impact on the stomach
What are sulindac, nabutemone and fenbufen examples of?
NSAID Pro-drugs
What type of drug is aspirin?
An NSAID
What NSAID is effective against mild pain and fever, and is a non-selective COX inhibitor?
Aspirin
What is Reye’s syndrome and what is it associated with?
A fatal disease associated with giving aspirin to children with viral illnesses such as chicken pox
What 5 groups of patient should aspirin not be given to?
CPBAL
Children (under 16)
Those with history of peptic ulcer (think GI side effects)
Those with Haemophilia or other bleeding disorders (anti-coagulant)
Patients on Anti-coagulant drugs
Those with liver disease
What could happen if you give aspirin to someone with a bleeding disorder or on an anti-coagulant drug?
It could make the effects worse
Why should you not give aspirin to people with a history of peptic ulcers?
They have negative effects on the GI Tract
What type of drug is ibuprofen?
An NSAID
What is the first choice NSAID drug and why?
Ibuprofen as it is slightly more specific to COX2, thus lower risk of side effects
What is naproxen?
An NSAID similar to ibuprofen but it is more potent and longer lasting - it has a longer half life = fewer doses
Name an NSAID similar to ibuprofen with a longer half life:
Naproxen
What are dexibuprofen, fenbufen, ketoprofen, diclofenac, indometacin, mefenamic acid and piroxicam examples of?
What are they similar to?
NSAIDs similar to ibuprofen
Most have fen in the name
What drug do we not know the mechanism of action for, that acts as an excellent antipyretic, and also as an analgesic?
(not a very good anti-inflammatory)…
Paracetamol
What drug do we use to reduce pain and fever?
Paracetamol
What drug can be used to treat children and also with ibuprofen?
Paracetamol
What 2 things does paracetamol mainly act as?
Antipyretic
Analgesic
Why do we give combined NSAIDs and opioid analgesics, even though they do not give greater relief than the opioid alone?
Less chance of dependence on the opioid
Which NSAIDs do we tend to combine with a weak opiate?
Aspirin or Paracetamol
What are co-codaprin and co-codamol examples of?
Combined NSAIDs and opioid analgesics
What does co-codaprin contain?
Aspirin and Coedine Phosphate
What drug contains paracetamol and coedine phosphate?
Co-codamol
Are co-codaprin and co-codamol available over the counter?
Yes
What is the drawback to combining NSAIDs with opioid analgesics?
Increased number of side effects
What drugs cause euphoria, analgesia and sleep?
Opioid Analgesics
Opioid Analgesics are from opium (poppy juice).
What 3 things can they induce?
Euphoria, analgesia and sleep
What are enkephalins, endorphins and dynorphins?
Opioid analgesics mimic them
3 chemicals naturally produced in the body that bind to opioid receptors
Natural ‘feel good’ chemicals
What type of pain are opioid analgesics used for?
Pain of visceral origin
What do we call pain resulting from surgery or terminal illness?
What do we use as an analgesic in this situation?
Pain of Visceral Origin
Opioid Analgesics
The dorsal horn releases enkephalin which usually binds to …………… receptors on the AO/C fibre. This then releases substance P which goes to the thalamus then spinothalamic tract causing pain. What drug stops this and how does it work?
Opioid receptors.
Opioids inhibit substance P release and this inhibits calcium influx needed to send the action potential up the tract to the thalamus
What is the gold standard opioid?
Morphine
What are coedine, dihyrocoedine and meptazinol used for?
What are they?
Opioids used for mild to moderate pain
What drugs do we use for mild to moderate pain?
Coedine, dihydrocoedine and meptazinol (opioids)
What drugs do we use for moderate to severe pain?
MDPBine and Tol
Morphine, diamorphine (heroin), pethidine, buprenorphine and tramadol (opioids)
What are morphine, diamorphine, pethidine, buprenorphine and tramadol used for?
Opioids used for moderate to severe pain
What drugs do we use for intraoperative analgesia?
during surgery
Fentanyl, alfentanil
When do we use fentanyl and alfentanil?
For inoperative analgesia
What do we use for postoperative analgesia?
Morphine
When do we use naloxone?
To combat an overdose of opioids - it binds to the opioid receptors to stop them binding more
What drug do we use to combat opioid overdose?
Naloxone
What type of drug do we use for acute and chronic pain (palliative care)?
What state does it put the patient in?
Euphoria and mental detachment
Morphine
What 5 ways can morphine be administered?
Intravenously Intramuscularly Subcutaneous Rectal Slow absorption in mouth
Why is morphine good for chronic pain? (Other than its pain relieving and euphoric effects)
It releases over time - sustained release
When morphine is infused by a syringe pump operated by the patient, what do we tend to call this?
Patient controlled anasthesia
What drug has the common side effects of constipation, nausea and vomiting, sedation, coughing, and confusion, nightmares and hallucinations?
Morphine
Morphine always produces which side effect?
Constipation (good for surgery)
What side effect results from morphine stimulating the chemoreceptor trigger zone in the brain stem?
Nausea and vomiting
What drug can patients potentially become dependent to or tolerant of, that can also result in respiratory depression (due to its effect on the medulla respiratory control centre)?
Morphine
When morphine is used in a therapeutic dose it can cause respiratory depression. In this scenario why is it not a bad thing?
You breathe fast when in pain anyway
What do you do if a patient starts to become tolerant to morphine?
Give a higher dose
Which sensory fibres are of small diameter and therefore more sensitive?
AO and C
How are lipid-insoluble local anaesthetics administered?
Why?
They are injected into the nerve axon as they can’t pass through the membrane
How are lipid soluble local anaesthetics administered?
Topically to skin or mucosal surfaces
When administering a local anaesthetic by subcutaneous injection to nerve endings with a vasoconstrictor - what should you beware of?
Being too close to peripheral areas such a finger tips - could result in tissue damage
What do we call the process where local anaesthetic is infiltrated around a nerve?
Nerve block
What is an uncommon method of administration for local anaesthetic in today’s hospitals?
Intravenous regional anaesthesia
What are lidocaine, bupivicaine, prilocaine and tetracaine examples of?
Local Anaesthetics - CAINE
What should we take caution to when administering analgesics?
Administering (where - which drug best)
Side-effects
Dependence
