Identification and quantitative determination of atorvastatin calcium polymorph in tablets using FT-Raman spectroscopy.

Atorvastatin calcium (ATC) is the active pharmaceutical ingredient (API) of the best selling lipid-lowering formulation Lipitor. Twelve ATC crystal forms are known and several pharmaceutical companies are developing or have developed generic drug formulations based on different ATC polymorphs. The strong overlap of the X-ray diffraction patterns (XRD) of the polymorphs with the respective patterns of the excipients, the presence of small API quantities in the tablet and the similarity of the crystal phase VIII XRD pattern used in the tablet examined in this work to that of phases IV and IX made identification difficult. Quantitative determination of ATC was attempted using Raman spectroscopy (RS), IR spectroscopy and X-ray powder diffraction. It was found that RS exhibited lower detection limit and a calibration model was constructed. Its application on commercial ATC tablets with 40mg strength yielded an error of 1.25%.