Analgesics + Soft Tissue Injuries Flashcards
What kind of NSAID is aspirin?
non-selective irreversible
What kind of NSAIDs are ibuprofen, naproxen and diclofenac?
non-selective reversible
What kind of NSAIDs are celecoxib, parecoxib and etoricoxib?
COX-2 selective
What kind of analgesic is paracetamol?
CNS-selective reversible COX-inhibitor
What are the opioid drugs?
mild: tramadol, codeine
strong: morphine, oxycodone, fentanyl
Cell membrane phospholipids are acted on by phospholipase A2 to form arachidonic acid. What 3 products are formed from AA and what are the enzymes used?
- Lipoxins (by 15-lipoxygenase)
- Prostanoids (by COX)
- Leukotrienes (by 5-lipoxygenase)
What are lipoxins, prostanoids and leukotrienes called collectively?
Eiconsanoids
Which types of inflammation are prostanoids and leukotrienes more selective for respectively?
prostanoids - acute inflammation
leukotrienes - chronic inflammation (and immune response)
Which enzymes do steroids and NSAIDs inhibit respectively?
steroids - phosphilipase A2 (affects all eicosanoids)
NSAIDs - cox (affects prostanoids)
What are 3 prostaglandins inhibited by NSAIDs?
PGI1 - prostacyclin
PGE2 - classical prostaglandins
TXA2 - thromboxanes
What are the effects of PGI2, PGE2 and TXA2?
- Prostacyclins (PGI2) → vasodilation (in closed wound); inhibition of platelet aggregation
- Classical prostaglandins (PGE2) → vasodilation or vasoconstriction; vascular permeability (edema); pain
- Thromboxanes (TXA2) → vasoconstriction (in open wound, thrombosis); platelet aggregation
Which 2 prostaglandins does aspirin block? What are the 3 physiological effects of this blockage?
PGE2 PGI2
- blocks vasodilation (hence less heat redness swelling)
- increases vasc permeability (hence less swelling)
- decreases pain
Explain why aspirin has an analgesic ceiling?
It blocks the production of prostaglandins, which sensitises the nociceptive fibres to stimulation by other inflammatory mediators
PG effect may already be turned off to the maximum but other signalling chemicals (eg. ATP, bradykinins, leukotrienes, K+) are still there
How do typical NSAIDs (eg. aspirin) exert CNS effect?
In infection, neutrophils increase IL-1 synthesis in the brain, which increases COX expression in the hypothalamus
This increases PGE2 levels resulting in fever
NSIADs that cross the BBB inhibit brain COX hence decreasing PGE2 in the brain and decreasing fever
What are the side effects of aspirin? (6)
- Reyes syndrome
- GI side effects
- Renal side effects
- Asthma
- Allergy/pseudoallergy
- Bleeding
What is Reye’s syndrome and what increases its risk?
Encephalitis and liver swelling
sx: vomiting, personality changes, listlessness, delirium, convulsions, loss of consciousness
increased risk in kids w viral infection, CI in children
What is the recommended duration of NSAID use to minimise GI SE?
Max 5 days
How do renal side effects arise?
Blockage of PGE2 and PGI2 in the kidneys, alters renal blood flow dynamics
PGE2 inhibits Na+ reabsorption at the TAL (25% reabs) → sodium retention, water retention, peripheral edema, HTN
PGI2 stimulates the secretion of renin and therefore aldosterone → hyperkalemia and acute renal failure
NSAIDs should be used with caution in patients with HTN or at risk of renal failure. What is triple whammy therapy?
NSAIDs, diuretics and ACEis
(NDA)
What are the risk factors for NSAID-induced AKI
old age, chronic HTN, atherosclerosis, pre-existing glomerular disease or renal insufficiency, volume depletion, cirrhosis or HF, use of ACEi or ARBs, use of triple whammy
Which mediator can trigger bronchospasms?
Leukotrienes
What is the sensitivity triad?
Asthma, chronic urticaria and nasal polyps
Will switching to another NSAID (with a different chemical structure) be helpful in pseudoallergy?
May not be effective as the pt is sensitive to COX inhibition and the rxn is not from antibodies against the chemical structure
What are 3 other typical NSAIDs and their important learning points?
- Naproxen - higher free fraction in women
- Indomethacin - strong (phospholipase A inhibition) but CNS SE
- Diclofenac - short half life and therefore low GI risk but gd for joint disease
Differentiate between COX1 and COX2 and how they contribute to side effects?
COX-1 is constitutive and usually results in “housekeeping” functions
COX-2 is inducible and usually causes inflammation
Most adverse effects come from the inhibition of COX-1 and therefore the inhibition of normal housekeeping functions
Selection of COX-2 over COX-1 (both produce PGI2 and PGE2) helps reduce GI and bleeding effects, but does not spare the patient from renal effects
What are the side effects of COX2 inhibitors? (5)
- Renal toxicity
- Effects on ovulation
- GI side effects
- Thrombosis risk
- Increased CV risk