IC 13: Drugs for Pain Management and Joint Pain Flashcards
What are the non-selective COX inhibitors?
- Irreversible COX inhibitor: Aspirin
- Reversible COX inhibitor: Naproxen, ibuprofen, diclofenac, mefanamic acid
What are the COX-2 selective inhibitors?
Celecoxib, parecoxib, etoricoxib (reversible)
What are the CNS-selective COX inhibitor?
Paracetamol (reversible)
What are the opioids/narcotic analgesics?
Tramadol, codeine, morphine, oxycodone, fentanyl
What is the difference between pain and nociception?
Pain: unpleasant sensory and emotional experience associated with actual or potential tissue damage
Nociception: detecting and signaling the presence of a noxious stimulus to the CNS
How do NSAIDs work?
They block phospholipase A2 enzyme which catalyses the release of arachidonic acid from the phospholipid molecule. Therefore, less stimulation of enzymes 15-lipoxygenase, cyclooxygenase and 5-lipoxygenase. There is less production of lipoxins, prostaglandins and leukotrienes.
What are some examples of prostanoids?
Prostacyclin, classical prostaglandins and thromboxanes
How do the various lipid molecules (prostacyclin, prostaglandin and thromboxanes) affect pain and platelet aggregation?
Prostacyclin: vasodilatation and inhibit platelet aggregation
Prostaglandin: vasodilatation, vascular permeability and pain
Thromboxanes: vasoconstriction and platelet aggregation
How do non-selective NSAIDs exert their anti-inflammatory effect?
- Blocks vasodilatation (less heating, redness and swelling)
- Decreases vascular permeability (less swelling)
- Block production of prostaglandins which sensitize the nociceptive fibres to stimulation by other inflammatory mediators
- Analgesic actions in the CNS
- Antipyretic
Are non-selective NSAIDs good for mild to moderate pain or severe pain? Why?
Mild to moderate pain. NSAIDs block sensitization of the pain and therefore there is an analgesic ceiling (if it gets too painful, patients will still feel the pain)
Is aspirin used often as a anti-inflammatory agent? Why?
No. Due to adverse effects of aspirin use as a pain killer, it is now over taken by paracetamol
What are the adverse effects of aspirin caused by at high doses?
Salicylate toxicity
What are some adverse effects of aspirin that are present even at low doses?
- Gastric intolerance (bleeding and hypersensitivity)
- Tinnitus (ringing in ears)
- Uricosuric (promote excretion of uric acid)
What life threatening syndrome is aspirin linked to?
Reye’s syndrome:
* Swelling of brain and liver
* Vomiting, personality changes, listlessness, delirium, convulsions, loss of consciousness
* Increased risk if it is taken by children with viral infections
What is naproxen often used for?
Dysmenorrhoea
Why is indometacin strongly anti-inflammatory?
Additional steroid-like phospholipase A inhibition
What is diclofenac often used as?
Use for inflammatory joint disease because of it’s long half-life in synovial (joint) fluid
What are the adverse effects of non-selective NSAIDs?
Hint: think of the different body systems
- GI: Dyspepsia, nausea, vomiting, ulcer formation and potential haemorrhage risk in chronic users
- Renal: Sodium retention, water retention, peripheral oedema, hypetension, suppression of renin and aldosterone secretion, hyperkalaemia, acute renal failure
- Pseudo-allergic reaction: skin rashes, swelling, itching, nasal congestion, anaphylactic shock
- Asthma: can trigger bronchospasm in suspectible asthmatics
- Bleeding: failure of haemostasis, bruising
What drugs constitute the triple whammy?
NSAIDs, diuretics, ACEi as they all reduce kidney function and increase risk of acute kidney injury
What are the risk factors for NSAID-induced AKI?
- Increasing age (>65)
- Chronic hypertension
- Atherosclerosis
- Pre-existing glomerular disease or renal insufficiency
- Volume depletion
- Use of ACEi or ARB
- Use of triple whammy
What patients are more susceptible to bronchospasm when using non-selective NSAIDs?
there are 3
Those with asthma, chronic urticaria and nasal polyps
What is the difference between COX-1 and COX-2 enzymes?
COX-1 = housekeeping
COX-2 = inducible (CNS, kidneys, female reproductive tract, synovium)
What are the unwanted effects of COX-2 inhibition?
- Renal toxicity due to constitutive expression of both COX-1 and COX-2 in the kidney
- Effects on ovulation, including delayed follicular rupture
- Premature closure of ductus arteriosus in late pregnancy
Can selective COX inhibitors be used in pregnancy?
Yes but not in third trimester
What is the impact of wound healing of COX-2 inhibitors?
COX-2 inhibitors impair wound healing and may exacerbate ulcers.
What is the effect of non-selective NSAIDs on thrombosis?
There is a relative increase in TXA2 which favours platelet aggregation and may increase risk of thrombosis
Why should there be greater caution when using NSAIDs in elderly or patients with a history of cerebovascular or cardiovascular disease?
NSAIDs except aspirin can increase the risk of heart attack, heart failure and stroke. This is due to the renal effects causing hypertension and the risk of prothrombic effects which together increases the risk of heart attack and stroke.
In what patients is the use of NSAIDs contraindicated?
- Severe kidney impairment
- Severe heart failure
- Active GIT ulcer or bleeding
- Bleeding disorders like haemophilia
- Use of systemic corticosteroids or antiplatelet agents/anticoagulants
- Multiple risk factors for NSAID toxicity (e.g. elderly patients with a history of GIT bleeding)
- Third trimester of pregnancy
How should NSAIDs be chosen for patients with risk of cardiovascular toxicity?
- Avoid diclofenac and COX-2 selective NSAIDs other than celecoxib
- Use celecoxib or ibuprofen limited to < 5 days
- If cannot use celecoxib, ibuprofen or naproxen, consider paracetamol alone
How should NSAIDs be chosen for patients with risk of GI toxicity?
- Avoid non-selective NSAIDs
- Use a COX-2 selective NSAID but with caution
- Consider co-prescribing GI protectant
How should NSAIDs be chosen for patients with risk of NSAID related bronchospasm?
- Avoid non-selective NSAIDs
- Use of COX-2 selective NSAID but with caution
Should NSAIDs be taken with food?
No as it can reduce absorption rate
What is the mechanism of paracetamol?
CNS-selective COX inhibition
What are the advantages of paracetamol?
- Good analgesic
- Potent antipyretic
- Spares the GI tract
- Side effects few and uncommon
- Few DDI
What are the disadvantages of paracetamol?
- Weak anti-inflammatory
- Toxic doses cause nausea, vomiting and liver damage
- Allergic skin reactions sometimes occur
In what patients should paracetamol be used with caution?
Hepatic dysfunction or alcohol abuse