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Drug shelf life estimation by non-isothermal treatments in DSC: Specific surface area effect

Abstract:

Isothermal methods for determining the stability of drug products are expensive and require a lot of time, non-isothermal ones are fast, require little sample and other resources; they allow to estimate the shelf life by considering the solid state chemical kinetics and can be used at an industrial level like alternative stability method. Samples of acetylsalicylic acid produced in different years by the same manufacturer, were submitted to a variable heating rate in a differential scanning calorimeter; the non-isothermal method of Kissinger allowed calculating the activation energy and the pre-exponential factor of the degradation. The dimensions of crystalline raw material particles were determined, smaller specific surface area involves a longer shelf life. The application of the non-isothermal Kissinger method allows the rapid determination of the remaining shelf-life of acetylsalicylic acid and to detect differences in activation energy possibly related to variations in composition, production process or storage. Considering the inverse relationship between Specific Surface Area and remnant shelf life; crystallization step should be carefully controlled to obtain crystals of 16 mm-1.