pH-independent drug release of an extremely poorly soluble weakly acidic drug from multiparticulate extended release formulations

Extended release mini matrix tablets for 8-Prenylnaringenin (8-PN), an extremely poorly soluble weakly acidic drug, were developed by using polyvinylacetate/polyvinylpyrrolidone as matrix former. Mini matrix tablets were manufactured by direct compression or wet granulation technique. With conventional modified release formulations, the drug demonstrated pH-dependent release due to pH-dependent solubility of the drug substance (i.e., increasing solubility at higher pH-values). In order to achieve pH-independent drug release two classes of pH-modifying agents (water-soluble vs. water-insoluble) were studied with respect to their effect on the dissolution of 8-PN. Addition of water-soluble salts of weak acids (sodium carbonate and sodium citrate) failed in order to achieve pH-independent 8-PN release. In contrast, addition of water insoluble salts of a strong base (magnesium hydroxide and magnesium oxide) was found to maintain high pH-values within the mini matrix tablets during release of 8-PN at pH 1 over a period of 10 h. The micro-environmental conditions for the dissolution of the weakly acidic drug were kept almost constant, thus resulting in pH-independent drug release. Compound release from mini matrix tablets prepared by wet granulation was faster compared to the drug release from tablets prepared by direct compression.