The stability of cefozopran monohydrochloride was studied by the non-isothermal method which was defined as a linear relationship between time and temperature. The value of activation energy (Ea) was calculated by applying the nonlinear least-square method. For the determination of the stability of cefozopran monohydrochloride in an aqueous solution, the respective Ea values at pH 2, pH 4 and pH 6 calculated by the non-isothermal method were 16.3, 21.8 and 20.7 kcal/mol (the mean value of Ea at 5°C/h and 10°C/h). The results were in good agreement with Ea value calculated by the isothermal method (pH 2; 16.2, pH 4; 21.8 and pH 6; 20.7 kcal/mol). For the determination of the stability of cefozopran monohydrochloride in a solid state, the Ea value calculated by the non-isothermal method was 18.7 kcal/mol (that calculated by the isothermal method was 19.5 kcal/mol). These results indicated that the non-isothermal method described in this paper could be adequately used for the stability study and was a rapid and accurate method for the determination of Ea values.
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