Pharmacology key concepts

1. H
   Half-life, volume of distribution and clearance

   Half-life is the time for a drug's plasma concentration to fall by half, and it depends on how widely the drug spreads and how fast the body clears it.

2. I
   Inverse agonists and constitutive receptor activity

   An inverse agonist is a drug that binds a receptor and lowers its signalling below the baseline (the resting level of signalling when nothing is bound to it).

3. O
   Ondansetron and 5-HT3 receptor antagonists in chemotherapy-induced vomiting

   Ondansetron is a 5-HT3 receptor antagonist: it blocks one of the receptors that serotonin acts on, and is given to prevent chemotherapy-induced vomiting.

4. P
   Potency versus efficacy on dose-response curves

   Potency (how much drug is needed) is read from the EC50, the concentration giving half the maximum response; efficacy (how big the effect can be) from the Emax, the maximum.

5. W
   Warfarin: mechanism and vitamin K dependent factors

   Warfarin is an oral anticoagulant that blocks the liver enzyme recycling vitamin K, so clotting proteins called factors II, VII, IX and X are made in an inactive form.

6. Why NSAIDs cause peptic ulcers

   NSAIDs (non-steroidal anti-inflammatory drugs) block cyclo-oxygenase (COX), the enzyme that makes the prostaglandins (local chemical messengers) protecting the stomach lining, so acid can then injure it.

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