NSAIDs Flashcards
What are the opposing effects of thromboxane A2 and PGI2/prostacyclin?
TXA2: plt aggregation, and vasoconstriction
PGI2: inhibition of plt aggregation, and vasodilation
Name four NSAIDs
Aspirin Ibuprofen Naproxen Diclofenac Celecoxib Perecoxib
What is the MoA of NSAIDs on COX enzymes?
Inhibition of the COX enzymes by competing with arachidonic acid for the hydrophobic site of COX.
Causes reduced formation of prostaglandins, prostacyclins and thromboxane A2.
Aspirin is an irriversible COX-1 inhibitor (slight COX-2 action).
What are the two mechanisms of the analgesic effects of NSAIDs?
Reduced PGE2 synthesis in the dorsal horn leads to reduced excitability of pain pathways. Full effect after several days of dosing.
Also acts at the site of inflammation and pain by reducing the synthesis of prostaglandins to reduce activation of the nociceptors.
What is the mechanism of the anti-inflammatory effects of NSAIDs?
Reduced production of prostaglandins - mainly PGE2 and PGD2.
Reduces vasoD and leakiness of BVs.
Full effect after several weeks e.g. for RA
What is the mechanism of the anti-pyretic effects of NSAIDs?
Inhibition of COX-2 in the hypothalamus.
Stops cytokine-induced prostaglandin synthesis here.
What is the mechanism of the anti-platelet effects of NSAIDs?
Inhibiton of COX-1 which reduces thromboxane A2 synthesis
Name a COX-2 selective NSAID
Celecoxib*
Etoricoxib
Parecoxib
How can the half-life of NSAIDs differ from theraputic duration?
NSAIDs accumulate at side of inflam, e.g. synovial fluid, so can have a theraputic action exceeding their half-lives
How do half-lives vary between NSAIDs?
Can be short: 1-5hrs
Or long: 10-60hrs
Can have modified release preparations to change half-life
NSAIDs are highly protein bound with a small Vd. What is an implication of this?
Can displace other drugs e.g. methotrexate, anticonvulsants, warfarin
Most NSAIDs are weak acids. What effect does this have on absorption?
Can be absorbed from the stomach
What is the mechanism of GI side effects?
Reduced prostacycling and PGE2 synthesis in the stomach leads to:
- Reduced mucus and bicarb secretion.
- Reduced mucosal blood flow.
NSAIDs are acidic, and can reduce the hydrophobicity of the mucus layer, allowing acid to cause damage.
State two GI side effects of NSAIDs
Dyspepsia Nausea Peptic ulceration Bleeding Perforation Exacerbation of IBD Local irritation and bleeding from rectal administration
Fewer ADRs in COX-2 selective
State a renal side effect of NSAIDs
More likely in CKD, CHF, cirrhosis with ascites, blood flow compromise
- Hypertension and oedema (due to salt and water retention bc of ↓GFR)
- Hyperkalaemia due to renin release