Impurities are normally generated during the formation of Active PharmaceuticalIngredients and their intermediates. Chances of their generation during Drug Productsformation are less as formulation is a physical blending process. Care is taken that theseexcipients do not react with each other to produce the degradants. They may consist oforganic and inorganic, and define levels at which impurities/degradants should beidentified.ICH Q3A covers drug substances and Q3B covers drug products. Th...