The goal of the physician is to dose the medicine so that it reaches the site of action at an effective and safe concentration. The absorbtion, distribution, metabolism and
excretion of the drug are affected by its biochemical properties, on the one hand, and by a number of patient factors, on the ohter; so a single dosing regimen may not be equally suitable for all. In complex populations, the pharmacokinetics of a drug may vary significantly between patients and change rapidly over time even within an individual patient. Understanding the basic principles of pharmacokinetics, the ability to take patient factors into account, and tailoring treatment regimens to the individual are the key to successful dosing.