Analgesia in Dentistry Flashcards
What happens in the arachidonic acid pathway?
Trauma and infection lead to the breakdown of membrane phospholipids producing arachidonic acid
This can be broken down to form prostaglandins
Prostaglandins sensitise the tissues to other inflammatory products, resulting in pain
Why do drugs aim to reduce prostaglandin production?
Prostaglandins don’t directly cause pain but sensitise tissues to other inflammatory products such as leukotrienes
If prostaglandin production decreases, this will moderate the pain
What are the properties of aspirin?
Analgesic
Antipyretic
Anti-inflammatory
What is aspirin’s mechanism of action?
Aspirin inhibits COX 1 and 2, reducing prostaglandin production
What are the adverse effects of aspirin?
GIT problems
Hypersensitivity
Overdose can cause tinnitus and metabolic acidosis
Aspirin mucosal burns due to salicylic acid
Give examples of groups that should avoid aspirin
Peptic ulceration - can cause perforation
Epigastric pain
Bleeding abnormalities ie - haemophilia
If on anticoagulants - aspirin enhances these
If under 16 - can cause Reye’s syndrome
Which groups should be cautious when taking aspirin?
Pregnancy/lactation - especially 3rd trimester
Patients on steroids as they may have a peptic ulcer
Renal/hepatic impairment - aspirin metabolised in liver and excreted in kidney
Hypersensitivity to/taking other NSAIDS
Elderly - more susceptible to drug induced side effects
G6PD deficient
What is Reye’s syndrome?
Fatty degenerative process in liver, profound swelling in brain
Up to 50% mortality
Caused by under 16s taking aspirin
What are the contraindications to aspirin?
Under 16s
Those breastfeeding
Previous or active ulceration
Haemophilia
Hypersensitivity to aspirin or other NSAIDs
What is the dosage of aspirin?
300mg tablets
2 tablets, 4 times daily, preferably after food
2.4g daily
Why is ibuprofen used?
Similar but not identical effect as aspirin
Less effect on platelets
Irritant to gastric mucosa but lower risk than aspirin
Paediatric suspension available
What is the adult dosage of ibuprofen?
400mg tablets
1 tablet 4 times daily, preferably after food
1.6g daily
In which groups should you be cautious when prescribing ibuprofen?
Previous or active peptic ulceration
The elderly
Pregnancy and lactation
Renal, cardiac or hepatic impairment
Hypersensitivity to aspirin/other NSAIDS
Asthma
If taking other NSAIDs
Patients on long term systemic steroids
Give examples of some side effects of ibuprofen
GIT discomfort, occasionally bleeding and ulceration
Hypersensitivity reactions eg rashes, bronchospasm
Headache
Dizziness
Drowsiness
What are some potential drug interactions of ibuprofen?
ACE inhibitors
Anticoagulants
Antidepressants
Corticosteroids
What are the symptoms of ibuprofen overdose?
Nausea
Vomiting
Tinnitus - more serious toxicity very uncommon
How may an ibuprofen overdose be treated?
Activated charcoal following symptoms if more than 400mg/kg has been ingested in the preceding hour
What are the properties of paracetamol?
Analgesic
Antipyretic
Little or no anti-inflammatory action
No effects on bleeding time
Doesn’t interact significantly with warfarin
Less irritant to GIT
Suitable for children
What is the mode of action of paracetamol?
Hydroperoxides are generated from the metabolism of arachidonic acid by COX and exert a positive feedback to stimulate COX activity
This feedback is blocked by paracetamol, indirectly inhibiting COX - in the thalamus
Exact mode still unclear
In which groups should you be cautious when prescribing paracetamol?
Hepatic impairment
Renal impairment
Alcohol dependence
What are the side effects of paracetamol?
Rashes
Blood disorders
Hypotension reported on infusion
Liver damage (sometimes kidney damage) following overdose
What are the drug interactions of paracetamol?
Cytotoxics
Domperidone
Lipid-regulating drugs
Metoclopramide
What is the adult dosage of paracetamol?
500mg tablets
2 tables 4 times daily
4g daily
How much paracetamol can it take to cause overdose?
As little as 10-15g (20-30 tablets) or 150mg/kg within 24 hours
Describe the results of paracetamol overdose
Causes severe hepatocellular necrosis and sometimes renal tubular necrosis
Liver damage is maximal at 3-4 days after ingestion
How do opioid analgesics work?
Act in the spinal cord, especially in the dorsal horn pathways, to regulate pain
Produce their effects via specific receptors which are associated with the neuronal pathways that transmit pain to the CNS
What are the problems with opioids?
Psychological and physical dependence
Tolerance - dose must be progressively increased to obtain effects
Can cause constipation and urinary and bile retention
What effects do opioids have on the CNS?
Depresses:
Pain centre
Higher centres
Respiratory centre
Cough centre
What are common side effects of opioids?
Nausea
Vomiting
Drowsiness
Larger doses produce respiratory depression and hypotension
What enhances the effects of opioids?
Alcohol
In which groups should you be cautious when prescribing opioids?
Hypotension
Hypothyroidism
Asthma
Decreased respiratory reserve
Pregnancy/breast-feeding
Hepatic impairment, renal impairment
Elderly
Convulsive disorders ie - epilepsy
Dependent
What are the contraindications to opioids?
Acute respiratory depression
Acute alcoholism
Raised intracranial pressure/head injury
Can codeine be prescribed dentally?
No - the only combination is dihydrocodeine
What is the dosage of dihydrocodeine?
30mg every 4-6 hours as necessary
What are the side effects of dihydrocodeine?
Nausea/vomiting
Constipation
Drowsiness
Larger doses - respiratory depression, hypotension
What are common drug interactions for dihydrocodeine?
Antidepressants MAOIs
Dopaminergics (Parkinsonism)0
In which groups should you be cautious when prescribing dihydrocodeine?
Hypotension
Asthma
Pregnancy/lactation
Renal/hepatic disease
Elderly/children
When should dihydrocodeine never be prescribed?
If raised intracranial pressure/suspected head injury
When is dihydrocodeine prescribed?
If patient has moderate to severe pain
Due to side effect of nausea and vomiting has little value for dental pain
Not very effective for post-op dental pain
What does opioid overdose result in?
Varying degrees of coma, respiratory depression and pinpoint pupils
Which drug can dentists prescribe for neuropathic and functional pain?
Carbamazepine
Give examples of neuropathic and functional pain
Trigeminal neuralgia
Post-hermetic neuralgia
TMJ or atypical facial pain
What other drugs are used to treat trigeminal neuralgia?
Gabapentin
Phenytoin
Not on the dental list
What are the clinical features of trigeminal neuralgia?
Severe spasms of pain - electric shock - lasts seconds
Usually unilateral
Older age group
Trigger spot identified
Females more than males
Periods of remission
Recurrences often greater severity
What is the dosage of carbamazepine?
100 or 200mg tablets
Starting dose 100mg once or twice daily, increased gradually according to response
Usual dose 200mg 3-4 times daily, up to 1.6g in some patients
