Abstract: This paper presents a three dimensional analysis of the complexity of the classical isothermal kinetic method for the stability prediction of pharmaceutical preparations and that of a simpler method multivariate linear model. By plotting the logarithm of time, ln(t), against the concentration function of drugs, lnf(c₀)-f(c), and the reciprocal of Kelvin temperature,1/T, the activation energy and shelf life of drugs can be calculated. An analytical comparison between the classical isothermal kinetic method and this model shows that the latter demands less experimental points and makes data treatment much simpler.