17: NSAIDs Flashcards
What is the overall MOA by which NSAIDs work?
By inhibiting the synthesis of Prostanoids via inhibiting of Cyclooxygenase 1/2 (COX) enzymes
Explain the synthesis of Prostanoids
- Essential phospholipids –> Phospholipase A2–
- Arachidonic acid –> COX1/2
- Prostaglandin H2 (PGH2)
- Prostanoids
What is PGE2?
A Prostaglandine –> in these notes: used as an example for the (complex) effects of prostanoids on the body
What are the unwanted actions of PGE2 on the body?
- Increased pain perception
- Increased body temperature
- Acute inflammatory response
- Immune responses
- Tumorigenesis
- Inhibition of apoptosis
Explain the analgesic effect of NSAIDs
Ihibit the PGE2-mediated lowering of pain threshold–> higher pain threshold via
- inhibition of cAMP mediated upregulation of P2X3 nocioceptors on cells
Might also
- increase the release of endocannabinoids
- beta-endorphin in spine
What is the role of PGE2 in pain perception?
How is this likes to inflammation?
- PGE2 binds to EP receptors
- increase in cAMP
- –> Activates P2X3 nocioceptors
- If only PGE2 –> only PKA increases expression of nocioceptors
But in Inflammation:
- •PGE2 + inflammation Epac pathway activated and additionally, more PGE2 produced
- Greater activation of P2X3 receptors –> more pain
Explain the role of PGE2 in body temperature regulation
PGE2 Stimulates hypothalamic neurones initiating a rise in body temperature
–> pyrogenic
Explain the anti-pyrogenic effects of NSAIDs
They inhibit the PGE2-mediated hypothalamic stimmulation of neurons that result in body temperature rise
How do prostanoids cause an effect in the cell?
Binding causes
- G-protein mediated (cAMP) as well as cAMP independant downstream mechanisms
What are the desirable effects of Prostanoids?
- Bronchodilation (although there is evidence that PGE2 can desensitise β2adrenoceptors)
- Gastroprotection
- Renal salt and water homeostasis
- Vasoregulation (dilation and constriction depending on receptor activated)
What is the role of Prostanoids in bronchial tone?
How does this influence the use of NSAIDs?
Normally: Prostanoids (PGE2) are brochiodilatory + protective
- NSAIDs might cause worsening of Astmah in Astmathics
- •NSAIDS should not be taken by asthmatic patients
Explain the role of PGE2 in the GI tract
In the stomach: Activated by COX 1
- decrease HCL production
- increase production of gastic mucus and Bicarbonate
- –> protective!
Explain the effects of NSAIDs on the stomach
COX1 inhibitors cause stomach ulcerations and many side effects due to
- inhibition of PGE2 mediated reduction of HCL and inhibition of production of mucus and bicarbonate
What is the MOA of Asperin?
It is a selevtive, irreversible COX1 inhibitor
- reduces prostanoid levels –> analgesic effect, anti-pytetic, etc.
- but also: reduced platelet aggregation in low dose–> becuase COX1 selective
- –> inhibtion of production of TXA2 but still production of Prostacyclin
Explaint the role of PGE2 in the kidney
- Dilation of afferent renal arteriole
- –> increase in renal artery flow
- increase in glomerular filtration rate
What are the effects of NSAID on the kidney?
•NSAIDs can cause renal toxicity
- •Constriction of afferent renal arteriole
- •Reduction in renal artery flow
- •Reduced glomerular filtration rate
- –> •Salt and water retention
What are the vascular side-effects of NSAIDs?
- Vasoconstriction
- Salt and water retention
- Reduced effect of antihypertensives
Might cause:
- Hypertension
- Myocardial infarction
- Stroke
Explain the difference in side-effects in selective COX1 and COX2 inhibitors
Though all NSAIDs increase risk of GI bleeds, ulcers and CVS events, it is far more likely for
- COX1 inhibitors to cause GI symptoms
- COX2 inhibitors cause CVS effects
What are the cardiovascular side-effects of COX2 inhibitors?
- On endothelium
- no limitation of platelet activation on plaques
- increase of coronary aterothrombosis
- decrease in NO
- no limitation of platelet activation on plaques
- Loss of protective function of Prostanoids on cardiac myocytes protection against arrythmias
- Kidney–> more salt+ water retention, deccreased GFR
- hypertension
- heart failure
Explain the risks and benefits of NSAIDs in analgesic and anti-inflammatory use
Analgesic use
- Usually occasional
- Relatively low risk of side effects
Anti-inflammatory use
- Often sustained
- Higher doses
- Relatively high risk of side effects
Which strategies could you use to minimise the side-effects of NSAIDs?
- Topical application
- In GI
- Minimise NSAID use in patients with history of GI ulceration
- Treat H pylori if present
- If NSAID essential, administer with omeprazole or other proton pump inhibitor
- Minimise NSAID use in patients with other risk factors and reduce risk factors where possible e.g.
- Alcohol consumption
- Anticoagulant or glucocorticoid steroid use
Summarise the side-effects of NSAIDs
- GI side effects
- risk of stomach ulcerations and bleed
- due to COX1 inhibition
- Kidney side effects
- salt and water retention
- HTN
- Haemodynamic AKI
- CVS
- stroke
- MI
What are the main side-effects of Asperin?
Why?
- Gastric irritation and ulceration
- Bronchospasm in sensitive asthmatics
- Prolonged bleeding times
- Nephrotoxicity
- Side effects likely with aspirin because it inhibits COX covalently, not because it is selective for COX-1
What is Ryes syndrome?
Syndrome occuring in viral infections and aspirin:
- Patients under 20
- Damage to mitochondria leading to ammonia production resulting in damage to astrocytes – oedema in brain –> severe outcomes
What kind of drug is Paracetamol?
Not clear
- cannot be counted as NSAIDs due to its very low anti-inflammatory effects
Explain the problem with Paracetamol overdose
Paracetamole is metabolised into NAPQI (intermediate product) that is very toxic
- Normally 2nd step metabolism by Glutathione
- But with overdose: accumulation of NAPQI that will bind to any SH group (present in many endogenous liver enzymes) and destroy the molecule
- Cell death and liver failure
Explain the effect and MOA of paracetamol
The MOA is Not understood, probably central and peripheral but it causes
- low-moderate analgesic effect
- anti-pyretic
Why has the number of deaths fromparacetamol overdose fallen steadily in England and Wales?
Legal restriction of over the counter dosage of paracetamol
Whay is Asperin an effective treatment in Rheumatoid Arthritis?
Asperin decreases PGE2 producion
PGE2 would
- bind to EP4 receptors
- dendritic cells and
- naive T-cells to
- increases production + proliferation of Th17
- produce IL-17 which is known to have destructive effects on bone and cartilage
