4 - Analgesia Flashcards
What are the common analgesics prescribed from the dental practitioners formulary?
- aspirin
- ibuprofen
- diclofenac
- paracetamol
- dihydrocodeine
- carbamazepine
How are prostaglandins produced?
- trauma/infection lead to breakdown of membrane phospholipids which produces arachidonic acid
- arachidonic acid breaks down to prostaglandins
What is the role of prostaglandins in pain?
- sensitise other tissues to inflammatory products which results in pain
- do not cause pain directly
What are the properties of aspirin?
- analgesic
- antipyretic
- anti-inflammatory
What is the mechanism of aspirin?
- inhibits cylco-oxygenases (COX1 and COX2)
- this reduces the production of prostaglandins
- COX1 inhibition reduces platelet aggregation
Describe the analgesic properties of aspirin.
- peripheral and central action
- peripheral actions are more dominant
- analgesia results from inhibition of prostaglandins in inflamed tissues
Describe the antipyretic properties of aspirin.
- prevents temperature raising properties of IL-1
- prevents rise of prostaglandins in the brain
- reduces elevated temperature, not normal temperature
Describe the anti-inflammatory properties of aspirin.
- prostaglandins act as vasodilators and affect capillary permeability
- due to the reduction in prostaglandins, inflammation is reduced at site of injury
What are the adverse effects of aspirin?
- GIT problems
- hypersensitivity
- overdose
- aspirin mucosal burns
Describe the GIT problems caused by aspirin.
- due to the COX1 inhibition, platelet aggregation is reduced which predisposes the GI mucosa to damage
- prostaglandins usually protect the mucosal lining by increases blood flow through gastric mucosa and produce mucin cells which have a protective lining
Who should not be prescribed aspirin due to GIT problems?
- ulcers
- gastro-oesophageal reflux
Describe aspirin hypersensitivity.
- acute bronchospasm (asthma attacks)
- skin rashes
- urticaria (hives)
- angioedema
Who should not be prescribed aspirin due to hypersensitivity problems?
Care should be taken when prescribing aspirin to asthmatics
Describe aspirin overdose.
- hyperventilation
- tinnitus (deafness)
- vasodilator and swelling
- metabolic acidosis
- coma
Describe mucosal burns caused by aspirin.
- direct effect of salicylic acid
- chemical burn of the mucosa when left in the mouth “to absorb”
- aspirin has NO TOPICAL EFFECT
Who is at risk when prescribing aspirin?
- peptic ulceration
- epigastric pain
- bleeding abnormalities or those on anticoagulants
- pregnancy or breastfeeding
- steroids
- renal/hepatic impairment
- U16s
- asthmatics
- hypersensitivity to other NSAIDs or taking other NSAIDs
- elderly
- G6PD deficiency
Why are those with peptic ulcers at risk using aspirin?
Ulcers could perforate under the effects of aspirin
Why are those with epigastric pain at risk using aspirin?
- could be due to reflux
- undiagnosed ulcer
Why are those with bleeding abnormalities at risk using aspirin?
Aspirin has anticoagulant properties
Why are those taking anticoagulants at risk using aspirin?
- aspirin enhances the effects of warfarin and other anticoagulants
- displaces warfarin from binding site on plasma and therefore increases free warfarin
- increases bleeding tendency +++
Why are those who are pregnant at risk using aspirin?
- platelet function is inhibited
- +++ risk for haemorrhage
- increased risk of jaundice of baby
- prolong/delay labour
Why are those who are breastfeeding at risk using aspirin?
Increased risk of Reyes syndrome (brain condition)
Why are those taking steroids at risk using aspirin?
Patients on systemic steroids are at higher risk of developing peptic ulcers, if undiagnosed may perforate if prescribed aspirin
Why are those with renal/hepatic impairment at risk using aspirin?
- aspirin is metabolised in liver and excreted in kidneys
- if renal impairment, excretion may be delayed/reduced
- not complete contraindication but reduce dose
How are nephrotoxicity and aspirin linked?
- prostaglandins are powerful vasodilators involved in control of renal blood flow and excretion of water and salt
- inhibition of prostaglandins (aspirin action) may result in sodium retention, reduced renal blood flow or renal failure
Why are those under 16 at risk using aspirin?
At risk for Reye’s Syndrome (50% mortality)
What is Reye’s Syndrome?
- fatty degenerative process in liver
- profound swelling in brain
- 50% mortality due to encephalopathy
Why are those with G6PD deficiency at risk using aspirin?
- glucose 6-phosphate dehydrogenase deficiency
- prevalent in individuals originating from parts of Africa, Asia, Oceana and Southern Europe
- susceptible to developing acute haemolytic anaemia
What are the complete contraindications for aspirin?
- under 16s and mothers who are breastfeeding
- previous or active peptic ulceration
- haemophilia
- hypersensitivity to aspirin or other NSAIDs
What is the standard dose of aspirin given for dental pain?
600mg x4 daily, after food
What is prescribed alongside aspirin to avoid GI problems?
- prescribed to those who have peptic ulcer (or history of) to prevent GI damage
- lansoprazole
- omeprazole
What is the standard dose of ibuprofen given for dental pain?
400mg x4 daily, after food
What is the maximum daily dose of ibuprofen?
2.4g
How does ibuprofen compare to aspirin?
- similar effect to aspirin
- less effect on platelets
- irritant to gastric mucosa but not as severe as aspirin
- can cause bronchospasm
- paediatric option available
What are the potential side effects of ibuprofen?
- GIT discomfort, occasionally bleeding or ulceration
- hypersensitivity reaction eg rash, angioedema, bronchospasm
- headache, drowsiness, depression, photosensitivity, fluid retention etc
What are the symptoms of ibuprofen overdose?
- nausea
- vomiting
- tinnitus
How do you treat ibuprofen overdose?
Activated charcoal if more than 400mg/kg ingested within an hour
What are the actions of paracetamol?
- analgesic
- antipyretic
Describe paracetamol.
- no anti-inflammatory action (peripheral)
- no effects on bleeding time
- does not interact with warfarin
- less irritant to GI
- suitable for children
What is the mode of action of paracetamol?
- hydroperoxides produced by the metabolism of arachidonic acid provide positive feedback to stimulate COX activity = more prostaglandins
- feedback is blocked by paracetamol
- especially effective in the brain and CNS
Who should be cautioned when taking paracetamol?
- hepatic impairment
- renal impairment
- alcohol dependence
What are the side effects of paracetamol?
- rashes
- blood disorders
- hypotension (infusion)
- liver damage (kidney sometimes) following overdose
What is the standard dose of paracetamol given for dental pain?
1g x4 daily
Describe paracetamol overdose.
- as little as 10-15g within 24 hours can cause hepatocellular necrosis
- liver damages maximal 3-4 days after ingestion, leads to liver failure and death
Where do opioid analgesics have their effect?
- spinal cord
- dorsal horn pathways
- central regulation of pain
What are some problems associated with opioid use?
- dependence
- tolerance (for drug to be effective dose needs to be progressively increased)
- constipation
- urinary and bile retention
What effect do opioids have on the CNS?
- depress pain centre (alters awareness)
- depress higher centre
- depress respiratory centre
- depress cough centre
What are the common side effects of opioid use?
- nausea
- vomiting
- drowsiness
- respiratory depression
- hypotension
- dry mouth
- bradycardia
- hallucinations
- dysphoria
- mood changes
- dependence
Who should be cautioned when taking opioids?
- hypotension
- hypothyroidism
- asthmatics
- decreased respiratory reserve
- pregnant or breastfeeding
What are complete contraindications for prescribing opioids?
- acute respiratory depression
- acute alcoholism
- raised intracranial pressure/head injury
What is the standard dose of dihydrocodeine given for dental pain?
30mg x4 daily
What are the side effects of dihydrocodeine?
- nausea and vomiting
- constipation
- drowsiness
What are potential drug interactions of dihydrocodeine?
- antidepressants MAOIs
- dopaminergics (used to treat Parkinson’s)
What are the symptoms of opioid overdose?
- coma
- respiratory depression
- pinpoint pupils
How do you manage opioid overdose?
Naloxone
What drug can be prescribed to treat trigeminal neuralgia?
Carbamazepine
What are the features of trigeminal neuralgia?
- severe spasm of pain described as electric shocks
- unilateral
- older age group
- trigger spot common
- more common in females
What is the standard dose of carbamazepine given for trigeminal neuralgia?
- 100-200mg once or twice daily
- max dose: 200mg x4 daily
- begin with lower dose and increase if ineffective
