A Novel Approach to the Study of Active Pharmaceutical Ingredients
Most active pharmaceutical ingredients (APIs) are manufactured, distributed and consumed as solids. Many APIs have multiple polymorphic forms, each of which can have distinct physicochemical properties such as solubility, melting point, and dissolution rate. In addition, APIs can also form pseudopolymorphs, which are the various hydrates and solvates with distinct sets of structures and bulk properties. Each of these unique forms may have widely varying bioavailability and stability, and also represent unique intellectual property. Therefore it is essential for the pharmaceutical industry to have reliable techniques for characterization of APIs at every stage in their development, including the bulk forms and the final dosage formulations (i.e., tablets and capsules).
Common methods for the characterization of solid APIs are thermal analysis methods, powder X-ray diffraction (PXRD) and 13C solid-state NMR (SSNMR)1. While all of these methods are adequate for characterizing bulk forms of APIs, they have serious limitations. For instance, pXRD can only be applied to crystalline samples, 13C SSNMR is limited in its capacity to distinguish peaks arising from structural differences and/or impurities. Additionally, these three techniques are not particularly useful for dosage forms, due to their complexity and interfering signals arising from the multiplicity of molecules within their excipient matrices.
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