Drug Substance and Excipient Characterization

Characterization of drug substances and excipients is a very important step at the preformulation phase of product development. Although testing will involve addi- tional time and cost, failure to carry out the appropriate characterization tests can be even more costly to manufacturers if the product made is not within specifi- cations. Preformulation characterization of raw materials creates a body of infor- mation which is very useful in the development of products. The lack of such information leaves the formulator with little leeway for remediation action when a problem arises from the production process or from the quality of the finished product. It is important to eliminate the possible influences of the raw material char- acteristics before venturing into investigation of processing variables. The knowledge derived from the characterization of raw materials can also serve to enable better specifications to be drawn up for procuring materials with the aim of either reducing cost or improving product quality. In addition, a review of material characterization results can provide an excellent database for the assessment of suppliers who can provide materials of consistent quality. Materials from reputable companies may be supplied with detailed speci- fications and their methods of determination may be obtained, if requested. The information on specifications such as purity or content is very often available. Nevertheless, it is prudent to confirm such information. The information provided by different suppliers may vary. The type of tests carried out or the techniques used for the characterization of a particular physical property, for example, the particle size distribution, may be different. Comparison of materials from different suppliers can therefore be difficult. Sometimes, the analytical result supplied by the manufac- turer is given as falling within a certain range and this gives virtually no information about batch to batch variation of the material. It is therefore important to have a system of in-house characterization of raw materials alongside the stability and functional tests for the finished product. When- ever possible, tests carried out should yield quantitative results rather than a pass/ fail or present/absent assessment. Retrospective studies of the finished product test