Characterization of a diltiazem-lambda carrageenan complex

In the present paper the interaction between lambda carrageenan, a natural sulphated polysaccharide, and diltiazem HCl, a Ca channel blocking agent, w as studied. Dialysis equilibria were performed to quantify the binding capa city of lambda carrageenan for diltiazem. The relevance of the interaction to hydrophilic matrix systems was confirmed: a relationship was found betwe en the binding capacity and the release profiles of matrix tablets containi ng a fixed amount of drug and different percentages of lambda carrageenan. Dialysis equilibria in buffered media showed that the interaction is quite insensitive to the pH of the medium (in the range 1.8-6.8), while it is red uced by increasing ionic strength; this behaviour is in lint: with the impo rtance of ionic bonds in diltiazem-carrageenan interaction. On the basis of the calculated binding capacity, the complex was prepared, dried and mille d. A preliminary characterization of the diltiazem-carrageenan complex in t he solid state was effected by means of X-ray and DSC analysis. The amount of drug going into solution from the complex was not significantly affected by the pH of the medium (in the range 1.8-6.8), while it was increased by increasing ionic strength. (C) 2000 Elsevier Science B.V. All rights reserv ed.