Thermal stability of disodium and calcium phosphomycin and the effects of the excipients evaluated by thermal analysis

In the present study, Thermogravimetry (TG) and Differential Scanning Calor imetry (DSC) are simultaneously applied to determine the thermal properties of two antibiotic salts, disodium and calcium phosphomycin, used either pu re or in association with several excipients. This study was carried out ki netically as well by mathematical elaboration of the TC curves performed ac cording to an isothermal procedure applied at different fixed temperatures. Kinetic parameters showing agreement with those produced by the isothermal method were also obtained by means of a non-isothermal method using a dyna mic TG curve alone. The main aims of the work were to provide reliable kine tic parameters (kinetic constant k, activation energy E-a and pre-exponenti al factor A) to evaluate the thermal stability of phosphomycin salts in the presence and absence of the excipients generally contained in the phosphom ycin-based pharmaceutical forms available on the market, and to obtain info rmation concerning compatibility towards the active components. These kinet ic parameters were then used to extrapolate shelf-life and half-life values at room temperature for pure active components ill the solid state and for their pharmaceutical derivatives. (C) 2001 Elsevier Science B.V. All right s reserved.