NSAIDS Flashcards
Summarise the use of NSAIDs in the U.K
Widely prescribed (16 million prescriptions annually in England)
6% patients reported possible adverse drug reaction- mostly in elderly patients
(> 15% elderly at any one time)
Available over the counter
Increased risk of GI and CVS
deaths
Ultimately, why are NSAIDs so widely used
Due to their analgesic, antipyretic and anti-inflammatory effects.
Summarise the analgesic effects of NSAIDs
Relief of mild-to-moderate pain (analgesic)
Toothache, headache, backache
Postoperative pain (opiate sparing)
Dysmenorrhea (menstrual pain)
Describe the anti-pyretic effects of NSAIDs
Reduction of fever (antipyretic)
Influenza
Describe the anti-inflammatory effect of NSAIDs
Reduction of inflammation (anti-inflammatory)
Rheumatoid arthritis
Osteoarthritis
Other forms of musculo-skeletal inflammation
Soft tissue injuries (strains and sprains)
Gout
Summarise how NSAIDs work
Inhibition of prostaglandin and thromboxane
synthesis
Lipid mediators derived from arachidonic acid
Cyclo-oxygenase enzymes
Widely distributed (virtually every cell)
Not stored pre-formed (so no need to deplete existing prostaglandins and thromboxane)
Receptor-mediated
Mechanism of Action: inhibit cyclo-oxygenase enzymes, preventing formation of prostaglandin H2 - hence limiting downstream prostanoid products
Describe the danger posed by NSAIDs
Although usually safe when used correctly, they can have extremely serious side-effects, particularly with long-term use or when used at high therapeutic doses.
§ Deaths from NSAIDs are on par with road traffic accidents (half due to GI upsets, and half due to CVS issues).
o ~2000 deaths/annum in 2011.
What are the main prostanoids
Prostaglandins (D2, E2 and F2a)
Prostacyclin (PGI2)
Thromboxane A2
What is the role of COX (1 and 2)
Arachidonic acid (from phospholipid membrane) – Prostaglandin H2 - this is the rate limiting step
Which is then converted by specific synthases to:
· Thromboxane A2
· Prostacyclin (PGI2)
· Prostaglandin D2, E2, F2a
Describe the naming of the prostanoid receptors
Naming based on agonist potency
Prostanoid receptors aren’t very specific - they are named based on which prostanoid they have the highest affinity for (e.g. DP1 has the highest affinity for PGD2)
State the prostanoid receptors
DP1, DP2 EP1, EP2, EP3, EP4 FP IP1, IP2 TP
Summarise the function of prostanoids
Prostanoids have both G protein-dependent and -independent effects (both desirable and undesirable)
Knock out mice show that prostanoid effects are extremely complex
Physiological and pro-inflammatory
What is PGE2 often referred to as
The ‘ringmaster’ prostanoid
Describe the formation of arachidonic acid in the phospholipid membrane
Physical, chemical, inflammatory and mitogenic stimuli stimulate the production of arachidonic acid from membrane phospholipids (catalysed by PLA2).
Describe the receptors that PGE2 can activate
PGE2 can activate 4 Receptors
(EP1-4)
cAMP-dependent and independent downstream mechanisms
EP1- Increased Ca2+ mobilisation
EP2,4- Increased cAMP
EP3-both
State the unwanted effects of PGE2
Increased pain perception Increased body temperature Acute inflammatory response Immune responses Tumorigenesis Inhibition of apoptosis
Plasticity and cell injury
What did a study on rats show about the effects of PGE2 (using a PGE2 analogue) on pain threshold
The PGE2 analogue reduced the pain threshold (i.e less stimuli was needed to ilicit a pain response).
Stimulation of PG receptors in the periphery sensitizes the nociceptors which cause pain both acutely and chronically.
EP4 receptor antagonist blocks the effect of the PGE2 analogue
Describe one mechanism of action for the noiciceptive effects of PGE2
PGE2 activates GPCR EP receptor (Gas) cAMP mediated (AC converts ATP -- cAMP) Activates P2X3 nocioceptors PGE2 only – PKA only PGE2 + inflammation Epac pathway activated and additionally, more PGE2 produced Greater activation of P2X3 receptors
EPAC and PKA pathways both mediated by cAMP
Describe some other mechanisms explaining how PGE2 causes pain perception
§ Activation of EP1 and EP4 receptors (in spine & periphery). - increase pain transmission
§ Endocannabinoid involvement. ((neuromodulators in thalamus, spine and periphery)
· This is not mutually exclusive – i.e. cross-talk between prostanoids and endocannabinoids
NSAIDS increase beta-endorphin in spine- an opiod neuropeptide
What is important to remember about aspirin
In addition, aspirin only is used as an anti-aggregatory drug to inhibition platelet aggregation in patients who are at risk of stroke or myocardial infarct
Describe the mechanism for the pyrogenic effects of PGE2 (upon stimulation by an inflammagen such as LPS)
PGE2 stimulates hypothalamic neurones initiating a rise in body temperature
This is why NSAIDs reduce your body temp if you have the flu
NOTE: there is a bit of a lag between PGE2 rising and temperature rising
Essentially, why do NSAIDs have so many side effects
The diversity of actions of prostanoids explains why inhibiting their synthesis with NSAIDs can have many unwanted effects.
Summarise the role of PGE2 in inflammation
PGE2 role in Inflammation extremely complex
Not generalisable
Which prostanoid receptor is responsible for signalling in acute inflammation
EP3 (on mast cells)
Which prostanoid receptor is responsibe for the effects of PGE2 on the immune system
EP4
Which diseases are treated with NSAIDs due to its effects on the immune system
Multiple Sclerosis and Rheumatoid Arthris (Th17 mediated) Contact Dermatitis (Th1 cells involved)
What is the problem with PGE2 inhibiting apoptosis
Inhibition of apoptosis increases the likelihood of necrosis
NOTE: there are 3 prostanoids, 7 prostanoid receptors and 2 downstream signalling pathways involved
Describe the beneficial, physiological actions 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)
Why should NSAIDs not be given to asthma patients
~10% asthma patients experience worsening symptoms with NSAIDS
Cyclooxygenase inhibition favours production of leukotrienes - bronchoconstrictors
Mouse Knockouts for mPGE2 synthase get aspirin-induced “asthma” , suggesting PGE2 is normally protective- lose bronchodilation effects of prostanoids.
NSAIDS should not be taken by asthmatic patients
Describe the gastric-cytoprotective effects of prostanoids (mediated by COX1)
PGE2 downregulates stomach acid production )parietal cells
PGE2 stimulates mucus production
PGE2 stimulates bicarbonate production
Dose-dependent reduction- more PGE2- greater reduction in production of gastric acid
Describe how NSAIDs increase the risk of gastric and duodenal ulceration
About half the deaths
from NSAIDs result from
gastrointestinal causes
o NSAIDs therefore increase the risk of ulceration à resulting in 1000 deaths/annum.
§ The ulceration is thought to be due to blocking of COX1…
§ Fewer deaths when using Celecoxib (COX2-selective inhibitor) rather than normal NSAIDs.
Summarise the two main isoforms of COX
COX-1 and COX-2 with different (but overlapping) cellular distributions
Aspirin is COX-1 selective and particularly bad at causes ulcers
Maybe COX-2 selective NSAIDS won’t cause ulcers
Coxib family: selectively reversibly inhibit COX-2 (example: celecoxib)
Very similar in structure- COX-2 just has a binding pocket in its active site that differs.
What are the main effects of PGE2 on the kidney
Increases renal blood flow
Describe how NSAIDs cause renal toxicity
o Renal toxicity via:
§ Constriction of afferent renal arteriole.
§ Reduction in renal artery flow.
§ Reduced glomerular filtration rate.
Describe the distribution of COX-1 and COX-2 in the nephron
Both expressed in the glomerulus
COX-2- ascending limb and macula densa
COX-1- DCT and collecting duct
As protanoids are complex vasoregulators, describe the unwanted cardiovascular effects of NSAIDs
NSAIDS can have serious unwanted cardiovascular effects Vasoconstriction Salt and water retention Reduced effect of antihypertensives 50% deaths from NSAIDs are cardiovascular Hypertension Myocardial infarction Stroke
Describe the relationship between the cardiovascular effects and COX-2 inhibitors.
Evidence that selective COX-2 inhibitors pose higher risk of cardiovascular disease than conventional NSAIDS even though mechanism is unclear
Outline a mechanism for the cardiovascular toxicity of coxibs (COX-2 selective inhibitors)
Related to its thrombotic and anti-platelet effect
they selectively inhibit PGI2 production whilst sparing the production of TxA2
PGI2 and PGE2 suppressed
Causes loss of control on mediators, which act phystiologically to instigate thrombosis
Increased BP and causes atherogenesis.
Non-selective NSAIDs and COX-2 selective NSAIDs both increase cardiac work
Also, all NSAIDs produce oxygen free radicals, which can contribute to cardiovascular disease
Outline a schemata for the cardiovascular effects of coxibs focussing on the vascular endothelial cell
Reduces PGI2
Leading to:
Unrestrained platelet activation onto ruptured coronary plaques- leading to an enhanced probability of coronary atherothrombosis
Also leads to a reduction in NO- which can also lead to unrestrained platelet activation but also cause heart failure.
Outline a schemata for the cardiovascular effects of coxibs focussing on the cardiomyocytes
Reduced PGI2 and PGE2:
Decreased protection against arrhythmias and oxidative injury
Leading to increased risk of HF
Outline a schemata for the cardiovascular effects of coxibs, focussing on the renal system
Cortical COX-2:
Reduction in PGI2:
Reduced renal blood flow and reduced GFR
Increased blood pressure- HF and increased long-term CVD risk
Medullary COX-2:
Decreased PGE2, leading to increased salt and water retention
This increases BP
Describe the spectrum of side effects of NSAIDs
All NSAIDS increase risk of GI bleeds and CVS events
But:
COX-1 inhibition (Piroxicam) à increased GI risk.
§ COX-2 inhibition (coxibs) à increased CVS risk
Ibuprofen lies in the middle
Summarise the risk vs benefit of NSAID use
Analgesic use
Usually occasional
Relatively low risk of side effects
Anti-inflammatory use
Often sustained
Higher doses- often in elderly whos metabolism is impaired anyway-worsening risk
Relatively high risk of side effects
Describe the relative GI and CVS risks of COX-1 selective and COX-2 selective NSAIDs when compared to non-selective NSAIDs.
COX-1 selective: · Same CVS risk as non-selective NSAIDs · Increased GI risk COX-2 selective: · Decreased GI risk · Increased CVS risk
Apart from giving a coxib, what else can be done to minimise the G.I side effects of NSAIDs
Topical application (to reduce dose)
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 (to decrease gastric acid production).
Minimise NSAID use in patients with other risk factors and reduce risk factors where possible e.g.
Alcohol consumption
Anticoagulant or glucocorticoid steroid use
Describe some of the ongoing developments of NSAIDs to make them safer
Dual COX and LOX inhibitors
For asthmatic patients
No safe option on the market (liver injury)
Nitric oxide or Hydrogen sulphide releasing NSAIDS
NO and H2S protective to GI and CVS
A number of options undergoing testing
Late stage clinical trials
What are the normal RENAL functions of prostanoids
Afferent arteriolar vasodilation (increased GFR)
Increased salt and water excretion
Therefore NSAIDS lead to:
Salt and water retention
HTN
Haemodynamic acute kidney injury
What are the normal cardiovascular functions of prostanoids
Vaascular (COX-2, PGI2)
vasodilation
inhibit platelet aggregation
Platelet (COX-1, TXA2)
vasoconstriction
Therefore, NSAIDs lead to stroke and MI
Summarise aspirin
Unique among the NSAIDS
Selective for COX-1
Binds IRREVERSIBLY to COX enzymes (binds covalently and acetylates the active site).
Has anti-inflammatory, analgesic and anti-pyretic actions
Reduces platelet aggregation
Describe the role of prostanoids on platelet aggregation
TXA2 (made by COX-1) released by platelets which encourages platelet aggregation
Prostacyclin (PGI2) (made by both COX-1 and 2)released by endothelial cells which inhibits platelet aggregation
Describe how aspirin reduces platelet aggregation
§ Reduces platelet aggregation.
o Platelets:
§ Reduces TXA2 production via COX1, no re-production as the platelet has no nucleus.
o Endothelial cells:
§ Reduces PGI2 synthesis by COX1/2. Reproduction possible due to nucleus.
o Thus, less TXA2 and still PGI2 so reduced platelet aggregation.
Why is it important to use low doses of aspirin
A low dose will allow the endothelial cells to resynthesise COX-1, which can then continue to produce prostacyclin
A high dose would mean that the COX-1 in the endothelial cells would be inhibited as it is being produced, thus decreasing prostacyclin production as well as thromboxane production
Inhibition of prostacyclin synthesis is proportional to inhibition of COX-2
We don’t want to inhibit prostacyclin production too much so we’d like to keep COX-2 inhibition low
Summarise the anti-platelet actions of aspirin
Very high degree of COX-1 inhibition which effectively suppresses TxA2 production by platelets
Covalent binding which permanently inhibits platelet COX-1
Relatively low capacity to inhibit COX-2
Use low dose to allow endothelial resynthesis of COX-2
Describe the unwanted effects of aspirin
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
Describe Reye’s syndrome associated with aspirin
Patients under 20
Viral infection and aspirin
Damage to mitochondria leading to ammonia production resulting in damage to astrocytes – oedema in brain
Summarise paracetemol
Is a widely used effective analgesic for mild-to-moderate pain which is available over the counter
Has anti-pyretic action
Has minimal anti-inflammatory effect
Therefore it is not a NSAID
Summarise the proposed mechanisms that may explain how paracetamol works
Not understood, probably central and peripheral
? COX- 3
? Via Cannabinoid receptors
? Interaction with endogenous opioids
?interaction with 5HT and adenosine receptors
Describe how paracetamol overdose may lead to irreversible liver failure
CYP2E1 converts N-acetyl-p-aminophenol to N-acetyl-p-benzochinon-imine (NAPQI)- THIS IS A TOXIC METABOLITE
Normally this toxic metabolite is mopped up by glutathione and converted into a reduced inactive form via glutathione-s-transferase
In overdose, the glutathione stores are depleted and the free toxic metabolite binds indiscriminately to any –SH groups
The –SH groups tend to be on key hepatic enzymes and this interference leads to cell death
Describe an antidote for paracetamol poisoning
Add compound with –SH groups
Usually intravenous Acetylcysteine
Occasionally oral methionine
Could be added to the formulation but increased cost
Acetyl cysteine used in cases of attempted suicide and accidental poisoning
If not administered early enough, liver failure may be unpreventable – transplant only option
Describe the legislation on OTC sales of paracetamol
Deliberate overdose more common than accidental poisoning
1998 pack size of paracetamol restricted to 16 x 500 mg tablets per pack
2009 guidelines stating
no more than 2 packs per transaction
Illegal to sell more than 100 paracetamol in one transaction
Since 2009, deaths from paracetamol overdose have fallen substantially, as have registrations for liver transplants
These have reduced the number of deaths caused by paracetamol overdose in the UK
Deaths have fallen by 43% since 2009.
What is the key difference between COX-1 and COX-2
COX-1 is constitutive (i.e. it is present all the time). It is found in many cell types and its main roles are in the regulation of homeostatic functions (make sure you can name some examples).
In contrast, COX-2 is mainly inducible and by cell types than COX1 and in particular by pro-inflammatory cells such as leukocytes. It has both pathological and physiological functions.
Describe the two steps in COX mediated AA metabolism
Both COX isoforms catalyse two different reactions. The first step is an oxygenation, which converts arachidonate to PGG2. The second step is a peroxidation, catalysed by a different part of the enzyme, which converts PGG2 to the product PGH2.
Why is aspirin different to all NSAIDs
Aspirin is different to all other NSAIDs because it binds irreversibly to cyclo-oxygenase enzymes. The consequences of this are that its actions are much longer-lasting than those of other NSAIDs and can only be reversed by de novo synthesis of new enzyme.
Aspirin binds 200-fold more avidly to COX-1 than to COX-2.
How may aspirin cause nephritis
Reduced creatinine clearance and possible nephritis
What are the NICE guidelines for coxibs
Those with a history of ulcers/GI bleeding
Patients over 65
Patients taking other drugs which increase risk of GI sideeffects
Patients needing maximal doses of NSAIDS long-term
Describe the roles of the different prostanoids
PGE2, PGF2, PGD2- pain, fever and inflammation
prostacyclin - vasodilation, anti-platelet, anti-atherogenic
TXA2- vasoconstrictor, pro-platelet, pro-atherogenic
