A drug stability experiment with dicloxacillin sodium in the solid state as a model was investigated by programmed humidifying method. A computer-controlled humidifying and heating system was established. The stability of drugs which were unstable to both heat and moisture could be studied by only one programmed humidifying experiment and one nonisothermal experiment instead of by many conventional classical isothermal experiments at constant relative humidity. In our established system, a pocket computer was used to control a common environmental chamber to obtain programmed humidifying and heating models. This controlling system was found to be quite accurate and reliable. The results from the experiments indicated that the kinetic parameters obtained were comparable to those from classical isothermal experiments.

Key words: drug stability, programmed humidifying experiment, nonisothermal experiment, degradation kinetics, dicloxacillin sodium