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Pharmaceutical Formulations Of Anthralin
Published 1981 · Medicine
A therapeutic action can occur only if the drug reaches the receptor sites in sufficient quantities. It is important, therefore, to ensure that the base does not interact with the drug thereby impeding its release, e.g. by complexing due to hydrogen bonding. On the contrary, the drug should have a much greater physico-chemical affinity for the skin substrate than it does for the base in which it is formulated. In addition, the drug particles in the base should have a minimum particle size to provide the maximum surface area for reactivity and optimal biological effectiveness. The best system is, therefore, a molecular dispersion in true solution. However, this advantage must not be outweighed by an affinity of the solvent molecules for the drug solute molecules so that the most efficient system will be provided by employing a solvent in which the solute is only poorly soluble but sufficiently so to provide enough drug in solution at saturation for therapeutic response. In order to ensure saturation over a range of tetnperatures it is preferable to include an excess of drug in the form of an amorphous or microcrystalline dispersion to provide a depot for rapid further dissolution. This also maintains saturation after the dissolved drug molecules start to partition into the skin substrate.