ON THE EMPLOYMENT OF LAMBDA-CARRAGEENAN IN A MATRIX SYSTEM .1. SENSITIVITY TO DISSOLUTION MEDIUM AND COMPARISON WITH NA CARBOXYMETHYLCELLULOSE AND XANTHAN GUM

Three anionic polysaccharidic materials, characterized by their differ ing sensitivity to pH, especially at low values, were compared in orde r to assess their behaviour on the performance in matrix systems. Lamb da-carrageenan, a sulphated polymer, was compared with two carboxylic polymers, Na carboxymethylcelluse (Na CMC) and xanthan gum. In the cas e of Na CMC both the gelation rate and the ionic charge are affected b y gastric pH. Gelation properties of xanthan gum are described as bein g more or less insensitive to pH. The more acidic lambda-carrageenan, however, was expected to maintain both gelation capability and ionizat ion even at low pH values. Erosion in distilled water and buffers at p H 1.2 and 6.8 was evaluated. Matrices containing as model drug either salbutamol sulphate or diprophylline were prepared and tested for rele ase rate in the same three media. Lambda-carrageenan shows characteris tic behaviour. Its control of the initial drug release, ascribed to io nic drug-polymer interactions, appears to be remarkably effective and independent of the characteristics of the dissolution medium.