Structural polymorphism of active pharmaceutical ingredients (APIs) is a
common phenomenon being a subject of continuous investigation. Depending on the
crystalline or amorphous form, APIs may have different physicochemical properties,
including solubility, which ultimately affects the various concentrations of the tested
polymorphic forms of the drug in body fluids. Currently, the different scanning
calorimetry and X-ray diffraction are the methods of choice in studies of structural
polymorphism of drugs. Three vibrational spectroscopic techniques namely: Fouriertransform
infrared, Attenuated total reflection and Raman spectroscopy may be
indicated as alternative, non-destructive, fast and cheap methods. In addition, the
theoretical approach based on quantum-chemical calculations and chemometrics
solutions is considered an important support in identification of various polymorphic
forms of drugs by determination of positions of bands and their intensities in analyzed
samples. In the first part of this chapter, we will focus on description of the differences
in the structure of crystalline and amorphous forms of APIs, their pharmaceutical
implications and characteristic of vibrational techniques that can be used in studies on
polymorphism of drugs. In the second part, we will present the most important
examples of the application of the above mentioned vibrational techniques to identify
polymorphic and amorphous forms of APIs with different profiles of pharmacological
activity and conventional and innovative excipients. Finally, the advantages and
limitations of vibrational spectroscopy to study the structural polymorphism of drugs
will be indicated and discussed.
Keywords: Active Pharmaceutical Ingredients, Amorphous form, Excipients,
Pharmaceutical Analysis, Pharmaceuticals, Physicochemical properties,
Polymorphous forms.
