In this work, solifenacin succinate (SOLS), flavoxate HCl (FLXHC) and tolterodine tartrate (TOLT) drugs were investigated using thermal analysis (TA) measurements in comparison with electron impact mass spectral fragmentation at 70 eV. Also chemical purity, melting point (using differential scanning calorimetry), activation energy and enthalpy in the process of characterizing medicines were important requirements evaluated in quality control of the pharmaceutical industry. The thermal decomposition of these drugs revealed a moderate stability up to 161, 215 and 195 degrees C for SOLS, FLXHC and TOLT drugs, respectively, before a complete decomposition in the temperature ranges of 161-800, 215-650 and 195-650 degrees C. The initial decomposition can be accounted for the loss of C7H12NO molecule, followed by loss of C20H20NO5 molecule for SOLS, loss of HCl, followed by loss of C24H25NO4 molecule for FLXHC, and loss of C23H30NO7 molecule followed by loss of C3H7 for TOLT drug. On the other hand, the molecular ion can easily fragmented by succinate, HCl and tartrate loss followed by loss of C2H5, C4H8 and C2H4 for SOLS, FLXHC and TOLT drugs, respectively. This is the best-selected pathway comparable with decomposition using TA. In addition, computational method including molecular docking was carried out to investigate the E. coli bacterial RNA (4p20) binding to the drug compounds under study. Molecular docking calculation indicated the existence of hydrogen bond and p-interaction between active sites of E. coli bacterial RNA (4p20) and O and or N and aromatic ring in all drug compounds which lead to their stabilization.
