Evaluating impurities in drugs: Part I of Part III

To ensure the quality of APIs and finished drug products, impurities must be monitored carefully during process development, optimization, and process changeover. The isolation, characterization, and control of impurities in pharmaceutical substances are being reviewed with greater attention based on national regulatory and international guidelines. In Part I of this article, the authors examine the different types and sources of impurities with specific examples. An impure substance may be defined as a substance of interest mixed or impregnated with an extraneous or usually inferior substance. The greatest financial impact on the cost of a drug substance often is found in the final preparation process. Product yield, physical characteristics, and chemical purity are important considerations in the manufacture of the active ingredient, the formulation of the dosage form, and the manufacture of the finished drug product. Processes to control the preparation of the drug substance and drug product must be disclosed to FDA as part of a new drug application.