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A new method is described for the assessment of the dissolution behavior of solid dosage forms. The method, which is based on the mass transfer between solid and liquid phase in an exchange column, is shown to avoid some disadvantages of the commonly used beaker methods employing fixed liquid volumes. Its usefulness is demonstrated by results obtained with nondisintegrating and uniform granules of benzoic acid in water. The influence of various external parameters, such as liquid flow rate, cell cross-sectional area, amount of material, and particle diameter, is found to agree with theory and literature data. Because of its reproducibility and the absence of arbitrary external parameters, the method seems to be useful for a meaningful study of dissolution kinetics.

The relationship between in vitro and in vivo drug release from Oros systems has been examined by analysing plasma concentration data from two pharmacokinetic studies, using a numerical deconvolution technique. This method generates an input profile by comparing the response with that achieved following an instantaneous reference unit dose. The approach is conceptually simple and does not require compartmental pharmacokinetic modelling or curve fitting. In the analysis of the first study, the plasma profile following intravenous dosing was used as the reference function, allowing the combined release/absorption process to be calculated; for the second, an oral bolus was used, the result of the deconvolution therefore indicating the in vivo dissolution rate of the Oros systems. The in vivo release from Oros in most volunteers followed the same pattern as that measured in vitro; only after 6-8 h was the decline in the in vivo release rate somewhat greater than expected. In a few individuals the cumulative absorption profile reached an early plateau level which coincided, on some but not all occasions, with the premature excretion of the Oros system from the body. The amount of drug in recovered systems agreed reasonably with the prediction of the deconvolution analysis.

In a recent series of papers, Kildsig and coworkers (1–4) investigated dissolution from compressed pellets in a static column of solvent, under conditions where the flat surface of the solid was either the lower or the upper boundary of the column (ascending and descending models, respectively). It was concluded that in the descending case an interfacial concentration, c1, significantly lower than the saturation concentration, c1, is operative and that c1, is related to energy parameters of the solid–liquid interface. The argument of the authors is not conclusive, however, and their experimental data can be interpreted in a more simple and convenient way which does not require the assumption of ct < cs.