Relationship between drug percolation threshold and particle size in matrix tablets

Purpose. Since a previous qualitative study carried out by us showed the existence of an important influence of the particle size on the percolation thresholds and taking into account that the existing theoretical models can only provide qualitative explanation to this influence, the purpose of this work is to carry out the first quantitative study of the influence of the particle size over the drug percolation thresholds. Methods. Matrix tablets have been elaborated using potassium chloride as drug model and Eudragit RS-PM as matrix forming material. Five different KCI particle size fractions have been employed whereas the Eudragit(R) RS-PM particle size was kept constant. In-vitro release assays were carried out for all the elaborated lots. The drug percolation thresholds were estimated following the method proposed by Bonny and Leuenberger. Results. A linear relationship has been found between the drug particle size and the corresponding drug percolation threshold. Conclusions. This finding confirms the results previously obtained in our qualitative study and has important repercussions in the design of pharmaceutical solid dosage forms. If this linear behaviour is general, the percolation threshold can soon become a useful preformulation parameter.