Aging dissolution characteristics

Naproxen sodium tablets were used in an in vivo-in vitro evaluation with four different polymeric dispersions, cellulose acetate phthalate (CAP), cellulose acetate trimellitate (CAT), 50 50 CAP/CAT, and methacrylic acid copolymer [64], The study indicated that coating material that dissolves at a more acidic pH in vitro (such as CAT at pH 4.5) will also dissolve at a more acidic pH in vivo (i.e., the coating dissolves higher up in the GI tract). In addition, it was found that aging did not markedly affect dissolution characteristics of CAT or methacrylic acid copolymer-coated tablets. 

The problem of alteration in dissolution characteristics on aging is typical to gelatin-based dosage forms. It is routinely faced by the manufacturers and, therefore, is a matter of concern. Fortunately, a lot of understanding has been developed over the period, since the time the problem was first recognized. The purpose of this article is to put the problem in the right perspective based on recent developments and the review of the reports in literature. 

Kimura, K., Hirayama, F, Arima, H. and Uekama, K. (2000). Effects of ageing on crystallization, dissolution, and absorption characteristics of amorphous tolbutamide-2-hydroxypropyl-beta-cyclodextrin complex. Chem. Pharm. Bull, 48, 646-50. [254]... 

As already demonstrated, for relatively recent sedimentary rocks and weathering crusts (20-200 Ma), the characteristic sequence of silica transformation is silica gel —> opal-A —> opal-CT —> chalcedony —> quartz. This is a well studied, polymorphous transformation of the solid phase transition type (a-cristobalite —> a-quartz) (Plyusnina 1983,1986,1990). One aspect of the solid phase transformations is the gradual transition of one silica phase to another and the gradual transformation of morphological features down the stratigraphic column with increasing burial depth and age (similarly in weathering crusts). The observed sequential cristobalite-quartz ratio would be unlikely to occur in rocks with repeated dissolution and crystallization from solution (Plyusnina 1983). 

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