Analgesia Flashcards
How does trauma and infection lead to pain?
- trauma and infection lead to the breakdown of membrane phospholipids
- this produces arachidonic acid
- Arachidonic acid can be broken down to form prostaglandins
- prostaglandins sensitise tissues to other inflammatory products resulting in pain
Arachidonic acid produces Leukotrienes when broken down, what does this result in?
- bronchoconstriction
- smooth muscle contraction
What products are formed from the Cyclooxygenase pathway?
Prostaglandins
protacyclin
thromboxane
what does thromboxane cause?
platelet aggregation
What are the properties of aspirin?
- analgesic
- anti-inflammatory
- antipyretic
Outline the mechanism of action for aspirin
- inhibits cycle-oxygenases COX 1 and COX 2
- thus reduces production of prostaglandins
Aspirin is more effective at inhibiting COX-1 than COX-2. What does this mean?
COX-1 inhibition reduces platelet aggregation
- predisposes to damage of the gastric mucosa
What are aspirin’s analgesic properties?
It is an NSAID so its analgesic action is exerted both peripherally and centrally
- mostly peripheral
- analgesic action results from inhibition of prostaglandin synthesis in inflamed tissues
outline the antipyretic properties of aspirin
- prevents temperature raising effects of interleukin-1
- thus reduces elevated temperature in fever
- does not reduce normal temperature
Outline the anti-inflammatory properties of aspirin
- prostaglandins are vasodilators
- therefore affect capillary permeability
- aspirin reduces redness, swelling and pain at injury site
What are the possible adverse effects of aspirin?
- mucosal aspirin burns
- GIT problems
- hypersensitivity
- overdose
Why can aspirin lead to GIT problems?
prostaglandins PGE and PGI2:
- inhibit gastric acid secretion
- increase blood flow through gastric mucosa
- help production of mucin by cells in stomach lining
- can lead to ulcers and gastro-oesophageal reflux
Why can aspirin cause mucosal burns?
- contains salicylic acid
- chemical burns occur when applied locally to oral mucosa
What groups should be avoided or approached with caution when prescribing aspirin?
- peptic ulceration
- bleeding disorders
- patients on anticoagulants
- pregnant or breast feeding women
- patients on steroids
- asthma patients
- hypersensitivity with NSAIDs
- u16s
- elderly
- Taking other NSAIDs
- renal impairment
When is aspirin completely contraindicated?
- under 16s
- patients with previous or active peptic ulceration
- patients with haemophilia
- patients with hypersensitivity to aspirin or other NSAIDs
Give 2 ways in which ibuprofen differs in effect from aspirin
- less effects on platelets
- irritant to gastric mucosa lesser than with aspirin
What is the maximum adult dose for ibuprofen?
2.4g
What is the treatment for ibruprofen overdose?
activated charcoal
Outline the mode of action for paracetamol
- hydroperoxides are generated from metabolism of arachidonic acid by COX, which then exerts a passive feedback stimulating COX activity
- feedback blocked by paracetamol, indirectly inhibiting COX
What properties does paracetamol have?
- analgesic
- antipyretic
Where is the main site of action of paracetamol?
the thalamus of the brain
When would you take caution for prescribing paracetamol?
patients with:
- hepatic impairment
- renal impairment
- alcohol dependence
What are the potential side effects of paracetamol?
- rashes
- blood disorders
- liver damage
What are the potential side effects of paracetamol?
- rashes
- blood disorders
- liver damage
What are the potential drug interactions of paracetamol?
- anti-coagulants (prolonged used may enhance anticoagulant effects of the coumarins)
- cytotocics
- lipid-regulating drugs
- domperidone
- metoclopramide
What is the maximum daily adult dose for paracetamol?
4g
How do opioid analgesics work?
- act in spinal cord
- central regulation of pain
Outline possible downsides of opiods
- dependence
- tolerance
- constipation
- urinary and bile retention
What are the side effects of opioids?
- nausea
- vomiting
- drowsiness
- respiratory depression and hypotension in larger doses
- dry mouth
- sweating
- bradycardia
- rashes
- palpitations
- hallucinations
- mood changes
- tachycardia
- mood changes
Which patients should be prescribed opioids with extra caution?
- hypotention
- asthma
- pregnant/breast feeding
- hypothyroidism
When are opioids completely contraindicated?
- acute respiratory depression
- acute alcoholism
- raised inter cranial pressure/head injury
What are the features of trigeminal neuralgia?
- severe spasms of pain: electric shock which lasts seconds
- usually unilateral
- older-age group
- periods of remission
- trigger spot identified
- more common in females
What is used to treat trigeminal neuralgia?
Carbamazepine 100 or 200mg 1-2x daily, dose may be increased gradually according to response
