Thermal stability of metronidazole drug and tablets

TG and DSC data were used to determine the thermal parameters of metronidazole drug and tablets. Three tablets A, B and C were analysed. The TG curves of metronidazole drug and tablets A and B displayed five and C four thermal decomposition processes, respectively. Analysis of the DSC data pointed to chemical interactions between metronidazole drug and the excipients of tablets, suggested by alterations in the melting point of metronidazole. The rate constants obtained from the isothermal TG data presents following sequence of the thermal stability: tablet A>tablet C>metronidazole drug>tablet B. This revised version was published online in July 2006 with corrections to the Cover Date.     

Correlation studies between thermal and dissolution rate constants of cimetidine drug and tablets

This work developed a methodology that can potentially be applied to the quality control of cimetidine drug substance and its tablets. The kT obtained at different temperatures (200, 190, 180, 170 and 160°C) were determined by isothermal thermogravimetric method using the classical Arrhenius equations. The dissolution profiles were obtained using USP 24 (Method 711) and rate constants (kD) were determined by Kitazawa equations. An evaluation was made to check if there was statistically significant correlation between the two variables kT and kD. Isothermal TG data were used to determine the reaction order and degradation reaction rate constants. The results showed that in all temperatures thermal order (kT) was: C<A<B tablets, while dissolution order (kD) was: C<A<B tablets. In conclusion, correlation between kT/kD seems to be a suitable method for detecting possible interactions between cimetidine and excipients in development or manufacturing changes, particularly for immediate release dosage forms and therefore could be especially useful on quality control. This revised version was published online in July 2006 with corrections to the Cover Date.