Thermal characterization of diltiazem and [lambda]-carrageenan binary systems

Interactions between diltiazem hydrochloride (DTZ), an orally active calcium antagonist used in the treatment of angina and hypertension, and lambda carrageenan ([lambda]CRG), which has been successfully used in matrix formulations to obtain constant and pH-independent release of basic drugs, were investigated in solid state using differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The effect of particle size on thermal behaviour of the drug and the polymer was assessed, and the result used to select the most suitable granulometric fractions for the study. Physical mixtures ranging in composition from 3:1 to 0.6:1 (by weight) drug-to-polymer ratios were analyzed as such and after kneading. A stoichiometric ratio of interaction of 1.6:1 (w/w) DTZ:[lambda]CRG was found, in agreement with that obtained from dialysis equilibrium studies. All the examined granulometric fractions (105 [micro]m) of the interaction product showed similar thermal behaviour.