NSAIDs

Question 1

what are the clinical uses of NSAIDs (5)

Answer 1

1. management of inflammatory disorders (osteoarthritis, opthalmological disorders, keratitis, uveitis)
2. management of pain (acute pain –> traumatic or surgical, chronic pain –> osteoarthritis, cancer pain, dental pain)
3. management of endotoxaemia in large animals (equine colic, bovine toxic mastitis)
4. management of prothrombotic states (feline hypertrophic cardiomyopathy)
5. management of tumours (some tumours are dependent on COX-2 activity, piroxicam used to treat transitional cell carcinoma of the urinary bladder)

Question 2

what are arachnidonic acid metabolites (eicosanoids)

Answer 2

COX1 and COX2 –> inhibited by aspirin, NSAIDs, selective COX-2 inhibitors

Question 3

what are the mechanism of action of NSAIDs

Answer 3

inhibit cyclooxygenase (COX)

COX is the enzyme which is responsible for the production of prostaglandins and thromboxanes

inhibiting COX therefore decreases the production of these mediators

Question 4

what do endogenous prostanoids have a role in

Answer 4

1. immune system
2. GI tract
3. cardiovascular system
4. kidney
5. lungs
6. reproduction
7. brain and spinal cord

Question 5

what are prostanoids

Answer 5

collective term for the cyclooxygenase metabolites of arachidonic acid and include prostaglandin (PG) D2, PGE2, PGF2alpha, PGI2 and thromboxane A2

Question 6

what is cyclooxygenase (COX)

Answer 6

COX is the enzyme which converts arachidonic acid to the prostaglandin precursor PGH2

A: arachidonic acid enters the COX enzyme channel and is converted first to prostaglandin G2 then to prostaglandin H2 (these steps not shown) then into a prostaglandin, the example shown is prostaglandin E2

Question 7

what is COX-1

Answer 7

constitutively expressed in most tissues

involved in normal homeostasis

many physiological functions - especially maintaining GI tract mucosa

up-regulated under stress conditions (nerve injury)

Question 8

what is COX-2

Answer 8

constitutively expressed in many tissues, including kidney, testicular ovarian cells and in the CNS

physiological functions: maintaining renal blood flow, nerve function, bone metabolism

induced in response to inflammatory stimuli

Question 9

how do NSAIDs block COX-1

Answer 9

bind to non-selective binding site to block arachnidonic acid from enetering the channel and converted to PG

Question 10

what is a COX continuum

Answer 10

two distinct genes for COX-1 and 2 may give rise to a number of constitutive and inducible COX proteins with overlapping functions

Question 11

how can NSAIDs be categorized

Answer 11

1. non-selective COX inhibitors (most commonly used ex. flunixin, ketoprofen)
2. preferential COX-2 inhibitors (carprofen, meloxicam)
3. specific COX-2 inhibitors (firocoxib, robenacoxib)

Question 12

what are the useful effects of NSAIDs

Answer 12

1. analgesic (central/peripheral)
2. anti-pyretic
3. anti-inflammatory
4. anti-thrombotic
5. anti-endotoxic
6. other uses –> cancer treatment

Question 13

what are the adverse effects of NSAIDs

Answer 13

1. GI –> dyspepsia, nausea and vomiting, ulceration
2. renal toxicity
3. hepatotoxicity
4. injury to articular cartilage
5. precipitate asthma

Question 14

what are the analgesic effects

Answer 14

1. peripheral action –> NSAIDs decrease PG production at site of inflammation –> reduced sensitization of nociceptive nerve endings to inflammatory mediators
2. central action –> NSAIDs block PG release and neuronal excitation –> reduced central sensitization

reduces hyperalgesia and pain

Question 15

how do NSAIDs reduce fever

Answer 15

the hypothalamus regulates normal body temperature –> ensures balance between heat loss and heat production

inflammation –> endogenous pyrogen (interleukin-1) –> COX –> PGE2 synthesis –> act on thermoregulatory centre in hypothalamus –> increase body temperature –> fever

Question 16

what are the anti-pyretic effects of NSAIDs

Answer 16

high concentration of PGE2 are found in CSF during infection

NSAIDs decrease production of PGE2 thus prevent increase temperature associated with fever

no effect on normal body temperature

Question 17

what are the anti-inflammatory effects

Answer 17

NSAIDs inhibit COX induction and release of prostanoids at site of inflammation to

1. decrease vasodilator prostaglandins (reduces edema)
2. reduces the inflammatory response (prevent peripheral sensitization)

Question 18

how do NSAIDS cause anti-thrombotic action

Answer 18

NSAIDs inhibit synthesis of thromboxanes (TXA2) –> inhibits platelet aggregation

more effective as anti-thrombotic agents at low doses

Question 19

what pathways do NSAIDs inhibit to cause anti-thrombotic action

Answer 19

Question 20

what are the anti-endotoxic action

Answer 20

endotoxins are lipopolysaccharides generated by gram -ve bacteria

endotoxins damage white blood cells and vascular endothelium thus releasing vasoactive mediators

triggers cascade of events which can result in endotoxemia

NSAIDs can prevent the generation of vasoactive mediators during endotoxemia

Question 21

what are the adverse effects on the GIT

Answer 21

PGs in the GIT

PGI2 and PGE2 in the gut protect the gastric mucosa by inhibiting gastric secretion, inducing vasodilation and increasing blood flow through gastric mucosa

COX-1 is primary isoform responsible for gastric mucosal PG production

COX-2 absent in normal gastric mucosa but induced rapidly in response to injury/gastric erosions

Question 22

what are the effects of NSAIDs in the GIT

Answer 22

inhibition of COX-1 –> reduction in PGs –> ulceration

mucosal ischemia

impairment of protective mucus barrier

exposing mucosa to damaging effects of acid

NSAIDs should be given with food to protect gastric mucosa –> contact area of the tablet results in high localized concentration of the drug increasing the potential for ulcer formation

Question 23

what are the roles of PGs in the kidney

Answer 23

PGE2 and PGI2 synthesized in renal medulla and glomerulus

involved in renal blood flow and excretion of salt and H2O via their vasodilatoru actions

modulate renal hemodynamics and excretion

PGE2 and PGI2 compensatory vasodilation

Question 24

what are the effects of NSAIDs in the kidney

Answer 24

1. inhibition of PGs impairs renal blood flow
2. in healthy well-hydrated animals, reduced renal PGs is of little consequence
3. can cause acute renal failure in conditions which depend on protective PGs
4. significant renal toxicity can occur in dogs and cats if they are volume depleted

Question 25

what are the pharmacokinetics

Answer 25

1. admin: most well absorbed following oral administration, with food, parenteral formuations also available 2. distribution: relatively small Vd (extracellular), highly plasma protein bound (\>99%), good penetration into acute inflammatory exudate 3. metabolism/excretion: generally by conjuction and renal elimination of metabolites (some biliary elimination), marked interspecies variability

Question 26

how do NSAIDs bind to COX-2 selectively

Answer 26

COX-2 channel is wider --\> NSAID will bind at 2 points and block it