Solid-state characterization and pharmaceutical compatibility between citalopram and excipients using thermal and non-thermal techniques

Differential scanning calorimetry (DSC) has been used in combination with powder X-ray diffraction (PXRD) and solid-state nuclear magnetic resonance (SSNMR) for evaluation of drug–excipient interaction. This study aimed to evaluate the antidepressive citalopram hydrobromide and the most usual excipient commonly used for the evaluation of their compatibility in binary mixtures. The TG/DTG curves reveal that citalopram is thermally stable up to 230 °C, presenting a sharp endothermic peak at 183 °C (Tonset = 185 °C) that corresponds to its melting point. Only for citalopram–lactose binary mixture was observed dislocation of the melting event in the DSC curves; however, this change has not indicated to be an interaction between the components in this case, but an overlap of events of lactose and citalopram. PXRD pattern suggests that no interaction is present between individual components that still showing the same crystalline structure for citalopram. The SSNMR spectrum assignment was done based on computational prediction of chemical shifts comparing it with its original spectrum. The chemical shifts confirmed the expected structure. Therefore, since changes in chemical shift are smaller than 1 ppm, no evidence of chemical interaction between the components of each binary mixture was confirmed.