Effect of Moisture on Solid Dosage forms. can the Arrhenius Equation be used as a Predictor?

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Abstract
It is shown that for pure (organic) solids, the Arrhenius equation is valid, except it may be difficult to elucidate the rate controlling parameter andor the predominant mechanism. The two most predominant mechanisms are Prout-Tompkins and Bawn kinetics. One aspects of kinetic investigations is to extrapolate so-called accelerated data (e.g. elevated temperature data), to other temperatures (e.g. room temperature). In such cases the Arrhenius equation is usually resorted to, but it is necessary, always, to establish the correct mechanism, extract from it the pertinent, rate-controlling parameters, and extrapolate these to room temperature. At times it is possible to obtain phenomenological parameters which can be extrapolated. In cases where solids are stored in the presence of moisture there are several subdivisions (a) cases where the moisture is in excess (plain Leeson-Mattocks model of non-ionizing substance) (b) cases where some of the moisture present is “bound”, i.e. not free to react, (c) the case of less than molar ratios of moisture to drug, (d) the case of adsorbed moisture, (e) the case of drug hydrates/anhydrate pairs.

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