In this chapter an overview will be given of the drug development process, which is both exciting and complex. We will focus on the development of new drugs and neglect developments based on existing drugs. Examples of the latter are improvements of the active ingredient (new ester, salt or non-covalent derivative, single enantiomer of a racemic drug, or the active metabolite of a (pro-)drug, new pharmaceutical formulations, new combinations and new indications). Of the drug candidates in development the majority belongs to the category of chemically synthesized small molecules (also referred to as new chemical entities, NCEs). However, in recent years an increasing number of drug candidates have been produced using biotechnological methods, the so-called biotech compounds, biologic(al)s or new biological entities (NBEs). Examples of the latter category are proteins, monoclonal antibodies (which are also proteins) and peptides, but also vaccines. Of the 28 new drugs approved in 2005 by FDA 8 were biologicals (29%). It is expected that over the coming years this percentage will remain between 25–35%.

The aim of drug development is to gather comprehensive information on the optimal use of a new drug in the treatment or prevention of disease, and to document the quality of the drug product. Efficacy, safety and quality are the main criteria for granting marketing authorization. However, it should be realized that clinical studies carried out during the development of a drug are not generating sufficient data to warrant the safety of a new drug. In fact, this aspect can only be appraised when there has been sufficient exposure to the drug in medical practice over longer periods of time.

For reasons of space we will not discuss the development of the production process nor that of the formulation and presentation form. The reader should appreciate, however, that this is a major part of the overall drug development process, subject to the highest quality requirements and a key factor in the regulatory approval and medical and commercial success of the drug.