Atenolol is the most used drug in Brazil to hypertension treatment. Two crystal structures are known for this molecule: a racemic form (R,S)-atenolol and a pure form S-atenolol. The racemic form is found in commercial tablets. X-ray powder diffraction (XRD) is an adequate tool to study crystalline structures including drugs. Using the Rietveld Method with XRD data it is possible to quantify the crystalline structures existing in the raw material. Other methods like Le Bail and Pawley can be used to the profile fit and phases identification. For this work we analyzed three tablets of atenolol, two generics and the reference (materials were purchased from a drugstore at the city of Araraquara). These tablets were analyzed by Rietveld, Le Bail and Pawley methods. All tablets exhibited the racemic mixture API (R,S)-atenolol. Some crystalline excipients could be characterized: magnesium carbonate hydrate, lactose monohydrate and talc. The conclusion is that the three methods can be efficiently used to characterize the three atenolol tablets.
During the last 20 years x-ray powder diffraction are being applied in our Laboratory to study pharmaceuticals ingredients and their products and in ceramics. In addition, we have dedicated a great effort in the teaching area, giving Rietveld and crystallographic courses in Universities, scientific events and industries (nearly three dozen in the last five years). Recently, the PONKCS method described by Scarlet and Madsen has been applied to the quantitative phase analysis (QPA), also in raw materials of pharmaceuticals and their products. Initially we realized that the PONKCS method provides better results than those obtained with the Rietveld method, especially when the atomic displacements are not provided with the CIF files. After some testing, we found that the fraction of a particular drug, as determined by RM, provides different results depending on the region of 2 measured, while with PONKCS it does not happens. With RM, to refine the atomic displacements in a pharmaceuticals can lead to serious problems in the QPA due to anisotropy, preferred orientation of the crystallites and high overlap of peaks caused by the low symmetry of the phases involved. With PONKCS it is not necessary to refine atomic displacement and this problem does not occur. This year, to celebrate 100 years of Crystallography, we are developing a course online, Characterization of organic and inorganic materials by diffraction of X rays by polycrystalline. We will present examples of PONKCS in pharmaceuticals and describe the online course.
Hydrochlorothiazide (HCTZ) is a diuretic used for the treatment of blood pressure (hypertension). HCTZ has two anhydrous polymorphs denoted as Forms I and II. Aiming at solid-state characterization, X-ray powder diffraction (XRPD) is known to be a powerful technique which has been successfully applied in investigating polymorphism in medicines. In this work, three tablets of HCTZ (a reference and two generic) were analyzed. The data were collected using Rigaku RINT2000 diffractometer copper rotate anode. The Rietveld method (RM) was applied for the characterization of HCTZ polymorphic form. For the crystalline excipients where the crystal structure is known, their phases were identified by the RM either. The results showed that all the tablets exhibit Form I of HCTZ, while the excipient lactose monohydrate is found to exhibit the crystalline form. One of the generics is also found to exhibit the excipient sodium lauryl sulfate (SLS) in the crystalline form. Therefore, the RM and XRPD are an efficient methodology for characterization of the crystalline Form I of the active principle of HCTZ and crystalline excipients lactose monohydrate and SLS in solid formulations. It is also interesting to observe excipients not described in the package insert of the medicament.
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