The principles of pharmacology (3).

This is the concluding part of a series of articles which examines the principles of pharmacology. This paper reviews the potential variability of an individual's response to drugs and the unwanted adverse reactions that may occur. Following this theme, the pharmacological considerations of the extremes of age will be briefly reviewed and the implications for perioperative practice highlighted. The reader is encouraged to use the reference list as indicative reading and complete the questions that appear during the text.