Poster Presenter

Comparative Study Between Cephalexine and Cefadroxil Thermal Behaviours
Adriana Fulias, Bogdan Tita, Dumitru Tita
România

In this abstract, thermoanalytical techniques were used to study thermal behaviour of cefadroxil and cephalexine. These substances are antibiotics from the cephalosporin family, known as a first generation cephalosporin used to treat certain infections caused by bacteria such as pneumonia and bone, ear, skin, and urinary tract infections.

Differential scanning calorimetry study was performed on Netzsch differential scanning calorimeter, model DSC–204, using aluminium crucibles under nitrogen atmosphere, with a constant flow of 50 ml•min^–1 and a heating rate β= 5, 7, 10 and 15 K•min^–1 up to a temperature of 500°C. Thermogravimetrical analysis was performed on Perkin–Elmer DIAMOND equipment in temperature range 25–550°C, using an air atmosphere and under dynamic conditions in order to study the thermal stability of the active substance.

DSC curves of cefadroxil (Fig.1.) show a sharp exothermic peak at ~210°C that corresponds to melting followed by thermal decomposition. The decomposition is defined in two exothermic stages. This is confirmed by TG/DTG curves (Fig.2.) that indicate thermal decomposition in the following temperature range: 191–320°C, 320–400°C and over 400°C a slow and continuous mass loss caused by elementary carbon formation from the previous steps, as consequence of the rupture of the azabicyclo and phenyl aromatic rings.

In the case of cephalexine, in both air and nitrogen (Figures 3 and 4), had rather the same behaviour, a clear decomposition step in a very narrow range, 180-200°C. The single and well developed DTG indicates probably a single step process. The exothermic DTA, even in nitrogen, is due to enough oxygen atoms in the molecule for the beginning of an intramolecular oxidation. The same values of the DTG and DTA maximum indicate a relative low exothermic effect.