The perfect drug would be along the lines of Paul Ehrlich's “magic bullet” – as illustrated in Figure 8.1, a drug molecule is readily administered, completely absorbed, moves to the desired therapeutic target site (receptor), does what it is supposed to, and is completely eliminated. The most pressing (and rewarding, if successful) area for drug development currently is optimizing the drug for a therapeutic target delivery as part of this process. One of the key steps in the nonclinical and clinical formulation of the drug is the selection of vehicles and of the inactive ingredients (excipients). Excipients are essential components of drug products in the United States and one must adequately address the safety of the proposed exposure to the excipients in those products. The specific safety data that may be needed will vary depending upon the clinical situation, including such factors as the duration, level, and route of exposure (that is, actual means of clinical drug administration).