Sustained release of highly water-soluble drugs with micelle forming ability from polyionic matrix tablets

The aim of present study was to evaluate the application of a hydrophilic matrix tablet capable of polyion complex (PIC-tablet) to a controlled-release device for highly water-soluble drugs. The PIC-tablet was prepared from a mixture of dextran sulfate and [2-(diethylamino)ethyl] dextran chloride, and diltiazem hydrochloride was used as a model drug. Release tests revealed that the drug release was sustained even in 50% drug loading and was influenced by ionic strength but not by pH in medium. The drug release mechanism was thus investigated from the viewpoint of drug micelle forming property. The micelle forming ability of diltiazem was examined by the conductivity method, and was found to be influenced by ionic strength but not by pH value in accordance with the release tests. The results suggested that the drug's micelle interacted with the polyionic matrix. Further studies were conducted using metoprolol tartrate and thiamine hydrochloride as cationic drugs and sodium cloxacillin and sodium salicylic acid as anionic ones. The release profiles of the micelle-forming drugs metoprolol tartrate and sodium cloxacillin were also suppressed in spite of different solubility or opposite ionic charge from diltiazem hydrochloride. These findings demonstrated that the PIC-tablet is a promising device for oral controlled release delivery of water-soluble drugs with good micelle-forming ability.