Estimation of the percolation thresholds in lobenzarit disodium native dextran matrix tablets

The objective of the present work is to estimate for the first time the percolation threshold of a new series of dextran (native dextran of high molecular weight [B110-1-2, Mw = 2 x 10(6)]), in matrices of lobenzarit disodium (LBD) and to apply the obtained result to the design of hydrophilic matrices for the controlled delivery of this drug. The formulations studied were prepared with different amounts of excipient in the range of 20% to 70% wt/wt. Dissolution studies were performed using the paddle method (100 rpm) and one face water uptake measurements were performed using a modified Enslin apparatus. The Higuchi, zero-order, and Hixson-Crowell models as well as the nonlinear regression model were employed as empiric methods to study the release data. Values of diffusion exponent 0.563 < n < 0.786 (Korsmeyer equation) for dissolution profile and water uptake mechanism 0.715 < n < 1 (Davidson and Peppas equation) suggested anomalous or complex mechanisms. On the other hand, the contribution of the relaxation or erosion and of the diffusive mechanism in Peppas-Sahlin equation indicated that the main mechanism for drug delivery from tablets is swelling controlled delivery (K(r)/K(d) < 1). The critical points observed in kinetic parameters above 58.63% vol/vol of native dextran B110-1-2 plus initial porosity in the LBD-dextran matrices with a relative polymer/drug particle size of 4.17 were attributed to the existence of an excipient percolation threshold.