LECTURE 1 Drug: general principles

Pharmacology – study of the effects of drugs on the function of living systems

What are Drugs?
- A chemical that affects physiological function in living organisms
- A substance that can be used in the diagnosis, prevention or treatment of disease

Sources of drugs…
    – Plants
    – Animals
    – Micro-organisms
    – Synthetic chemistry
    – Genetic engineering (biotechnology)

Majority of the important drugs act on the following Types of Regulatory Proteins:
1) Receptors
2) Ion channels
3) Enzymes
4) Carrier molecules (transporters)

(1) Receptors
Sensor in a system of chemical communications, which coordinate different functions in various cells in the body.

(2) Ion Channels
    – Passage (through the cell membrane) for ions to enter or exit a cell.
    – Divided into 2 types:
          1) Ligand-gated ion channels – possess receptor(s)
              - Ligand: any substrate which binds to a receptor
          2) Voltage-gated ion channels – trigger by action potentials
    – e.g.   local anaesthetics, calcium antagonists

(3) Enzymes
    – Proteins which catalyze reactions to render a product
      1) Agonist would render an useful/active product
      2) Antagonist
                - Can inactivate an enzyme temporarily or permanently
                - Combine with an enzyme and render an inactive product
      3) Pro-drug would be converted to its active form by reaction(s) catalyzed by an enzyme.   e.g. prednisone, enalapril
Carrier molecules
    – Cell membranes are lipophilic (Structure of cell membrane)
    – Most of the permeating molecules are too polar (contains too much charges) pass through the cell membrane.   Binding sites on carrier molecules are specific for the molecules to be carried.
      e.g. transport of glucose and amino acids into cells
    – This makes it another target for drug actions.
      e.g. omeprazole, loop diuretics