ABSTRACT
Pharmacodynamics is the study of effects of drugs on biological processes. An example is shown in Figure 2.1, demonstrating and comparing the effects of a proton pump inhibitor and of a histamine H2 receptor antagonist (both drugs used for the treatment of peptic ulceration and other disorders related to gastric hyperacidity) on gastric pH. Many mediators exert their effects as a result of high-affinity binding to specific receptors in plasma membranes or cell cytoplasm/nuclei, and many therapeutically important drugs exert their effects by combining with these receptors and either mimicking the effect of the natural mediator (in which case they are called ‘agonists’) or blocking it
(in which case they are termed ‘antagonists’). Examples include oestrogens (used in contraception, Chapter 41) and antioestrogens (used in treating breast cancer, Chapter 48), alphaand beta-adrenoceptor agonists and antagonists (Chapters 29 and 33) and opioids (Chapter 25).
