NSAIDS

Question 1

Describe the pharmacokinetic effects of NSAIDS

Answer 1

Given orally or topically

Most show first order (linear) elimination kinetics

Some have short t1/2 (e.g. Ibuprofen) some have longer t1/2 (e.g. Naproxen)
Aspiring has dose-dependent kinetics (zero order at higher doses)

Heavily bound to plasma proteins and can displace other plasma proton binding drugs

Question 2

What are the adverse drug reactions of NSAIDS

Answer 2

Mainly due to inhibition of COX1 (constitutively secreted to produce prostaglandins ordinarily)

GI: reduction in mucus production and acid secretion (damage to stomach: ulceration, haemorrhage, perforation)

Renal: in susceptible individuals (neonates/elderly) can reduce GFR and perfusion of kidney

Vascular: increased risk of prolonged bleeding time, bruising, haemorrhage (inhibit thromboxane A2), so reduced platelet aggregation

Hypersensitivity: skin rashes (Stevens Johnson Syndrome), asthmatic bronchospasm

Question 3

What are NSAIDS used for

Answer 3

Mild-mod pain in isolation

Chronic pain from inflammation in combination with other drugs

Question 4

DDIs of NSAIDS

Answer 4

Can be used in combination with low dose opiates, extending therapeutic range for treating pain (and reduce ADRs of opiate use)

Combining multiple NSAIDS can increase risk of ADRs: affect eachother’s binding of plasma protein (e.g. Aspiring + NSAID: compete for COX1 binding site, reducing cardioprotective mechanism of aspirin)

Some drugs displaced by NSAIDs and may require dose adjustment:
Sulphonylurea: hypoglycaemia
Warfarin: increased bleeding
Methotrexate: range of serious ADs

Question 5

What is special about Aspirin as an NSAID?

What other therapeutic uses does it have?

Answer 5

Only NSAID that irreversibly binds COX enzymes via acetylation (i.e. Not by competitive blocking)

Also used in arthero-thrombotic disease (anti-platelet: prevents thromboxane A2 production)
And in GI cancer prophylaxis (

Question 6

What class of drug is paracetamol
What is its mechanism of action
Describe its pharmacokinetics

Answer 6

Chemically related to NSAIDs but has no anti-inflammatory action: is a non-NSAID non-opiate analgesic

Action uncertain but appears to selectively inhibit COX activity in CNS (better ADR profile)

Linear PK (first order) at normal doses: 90% enters phase 2 metab (glucoronidation/sulphonation) and 10% enters phase 1 oxidation to produce NAPQI

Non-linear (Zero order) at high doses: phase 2 metab saturated, increasing phase 1 metab and production of NAPQI - a toxic metabolite that depletes glutathione (during detoxification in phase 2 conjugation)
Unconjugated NAPQI is neutrophilic: loss of hepatic cell function and potential for renal failure

Question 7

How is paracetamol overdose treated

Answer 7

0-4hours: activated charcoal orally (reduce uptake)

0-36 hours: n-acetylcysteine IV (or methionine oral) to increase glutathione

Question 8

How are prostaglandins made

Answer 8

Phospholipids from cell membrane cleaved to arachidonic acid (using enzyme phospholipase C or A2)

Arachidonic acid can either enter the leukotrine or prostaglandin pathway

Prostaglandin pathway involves metabolism or arachidonic acid to prostaglandin H2 by COX 1 & 2 enzymes

Once PGH produced, specific prostaglandins can then be produced (most inportantly PGE)