Compatibility between active components of a commercial drug.

A thermal and a kinetic analysis on the decomposition processes of a commercial drug named diamplicil (AD), obtained by an antibiotic combination of ampicillin (A) and dicloxacillin (D), have been carried out to find their thermal stability. The DSC/TG curves of this commercial drug were compared with those of its active components and an excipient, the magnesium stearate (M). Kinetic study was carried out using both isothermal and dynamic TG curves. Decomposition mechanisms for both active components and commercial drug tested were not found. The kinetic data obtained by the non-isothermal isoconversional method showed that D component causes a decrease of the kinetic stability of the active A component. Additive magnesium stearate does not decrease the stability of the two components. Moreover, storage time values at room temperature were calculated.