Abstract
The aims of the present investigation were to compare the dissolution properties of dimemorfan phosphate and dimemorfan and to control the dissolution of dimemorfan species, which are pharmacologically equivalent, by using suitable mixtures of dimemorfan phosphate and dimemorfan. The solubility of dimemorfan was studied in solutions of various pH values. It was almost constant at low pH, reached a maximum at pH 6.6, and decreased significantly with further increase of pH. Dissolution rates were determined in solutions of various pH values. Dissolution rate of dimemorfan phosphate increased gradually with increase of pH of the dissolution medium, whereas that of dimemorfan decreased. It is suggested that in the case of dimemorfan dissolution, the pH value of the saturated layer is influenced profoundly by the nature of the dimemorfan species, though the effect is small in the case of dimemorfan phosphate because of the existence of phosphate ions in the compound. Based on an analysis of the dissolution properties of dimemorfan species in solutions of different pH values, a method for controlling the release of dimemorfan species was established by the use of mixtures of dimemorfan and dimemorfan phosphate.
