Pain Management Flashcards
COX enzyme differences
COX 1 has tighter active site shape
COX 2 could be specifically targeted by using larger drugs
COX enzyme function
Convert arachidonic acid to prostaglandins G and H
COX 1 is generally cytoprotective
COX 2 is induced by injurious stimuli, may be constitutively expressed in brain and kidney
Prostaglandin role in pain
Mainly PGE
EP1 receptor - increased bradykinin sensitivity, K+ channel inhibition, increased Na+ channel sensitivity
EP2 receptor - decreased glycine receptor affinity
EP3 - pyrexia
NSAIDs therapeutic effects
Via COX 2 inhibition
Prevents arachidonic acid conversion to PGs
Analgesia
Anti inflammatory
NSAID pharmacokinetics
Oral or topically if soft tissue injury
Heavily protein bound (90-99%)
Linear pharmacokinetics within therapeutic dose range
T 1/2 - two groups - more than 10 hours (naproxen) or less than 6 (ibuprofen)
NSAID DDIs
If two NSAIDs unknowingly given together
Protein displacement-sulfonylureas, warfarin, methotrexate
NSAIDs ADRs
Hypersensitivity - aspirin induced asthma, skin rashes. Don’t give in asthma because leukotrienes
Reye’s syndrome - rare, serious - brain/liver injury
Stevens-Johnson syndrome - rash of skin and mucous membranes
Increased clotting time
Renal (reduced blood flow - PGE2 and I2 maintain renal blood flow)
GI - peptic ulcers
Ibuprofen
NSAID
Aspirin
NSAID
Irreversible COX inhibition (acetylation)
Antiplatelet
Anti GI and breast cancer?
Rofecoxib
Celecoxib
COX 2 inhibitors
COX 2 inhibitors
Should have fewer ADRs
Short term use only
Paracetamol mechanism
Unknown - weak COX inhibitor
Perhaps on COX 3 isoform in CNS
Paracetamol pharmacokinetics
First order in healthy patient
T1/2 2-4 hrs
Caution if poor hepatic function
Paracetamol toxicology
NAPQI made - depletes glutathione - hepatocyte death Also renal failure Give N acetyl cysteine in first 36 hrs Methionine if can't be given promptly Activated charcoal in first 4 hrs
Endogenous opioids
Endomorphins 1 and 2 (mu receptor)
Enkephalins - metenkephalin, leuenkephalin
Endorphins (from POMC)
Newly discovered - nociceptin, nocistatin
Opioid receptors
Mu (MOP) in CNS (supra spinal) - analgesic via increased K+ efflux
Delta (DOP) widely distributed in CNS. Bind enkephalins, work via decreased cAMP synthesis
Kappa (KOP) in spinal cord - analgesia via calcium channel block