Study of the critical points and the role of the pores and viscosity in carbamazepine hydrophilic matrix tablets

Percolation theory has been applied to estimate the Hypromellose (HPMC) percolation thresholds and the influence of the polymer viscosity and the initial porosity on these thresholds in carbamazepine multicomponent matrix formulations.Different batches containing two viscosity grades of HPMC as hydrophilic matrix forming polymer, MCC and lactose as fillers, and a lubricant mixture have been manufactured varying the compression pressure in order to obtain matrices with three levels of initial porosity. The results suggested the existence of an excipient percolation threshold between 13 and 15% v/v of HPMC for the different batches prepared. It has been found that the percolation threshold for this polymer is independent on the formulation factors studied in this paper: polymer viscosity and initial porosity of the matrices.

The figure shows that when low percentages as 15% of HPMC are employedin hydrophilic matrices manufactured with different viscosity grades of HPMC and different initial porosity levels, the porosity of the matrices exert much more influence in the drug release rate than the polymer viscosity.Figure optionsDownload as PowerPoint slide