AAPS PharmSciTech

, Volume 11, Issue 2, pp 558–562 | Cite as

Polymer Percolation Threshold in HPMC Extended Release Formulation of Carbamazepine and Verapamil HCl

  • Tamara Gonçalves-Araújo
  • Ali R. Rajabi-Siahboomi
  • Isidoro Caraballo
Research Article


The principles of the percolation theory were applied to further understand and design hydroxypropyl methylcellulose (HPMC) extended release matrix tablets containing carbamazepine and verapamil HCl. This statistical theory studies disordered or chaotic systems where the components are randomly distributed in a lattice. The application of this theory to study the hydration and drug release of hydrophilic matrices allows describing the changes in hydration and drug release kinetics of swellable matrices. The aim of this work was to study and develop extended release matrix formulations for carbamazepine and verapamil HCl, containing hypromellose (HPMC, METHOCEL™ Premium K100M CR) as rate controlling polymer using the concepts of percolation theory. The knowledge of the percolation threshold of the components of the matrix formulations contributes to improve their design. First, reducing the time to market and second, avoiding to formulate in the nearby of the percolation threshold, which will result in a lower variability. Therefore these formulations will be more robust when they are prepared at industrial scale. The HPMC percolation threshold for drugs with very different water solubilities was determined and it was shown that there was no significant influence of drug solubility on the HPMC critical concentration threshold (excipient percolation threshold). This may be related to the versatility and broad functionality of the swelling hydrophilic matrices.

Key words

carbamazepine extended release hydrophilic matrix hypromellose verapamil HCl percolation theory 



The authors wish to express their gratitude to Colorcon for funding this study and for the supply of METHOCEL™ and Recordatti for the supply of the carbamazepine and verapamil HCl.


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Copyright information

© American Association of Pharmaceutical Scientists 2010

Authors and Affiliations

  • Tamara Gonçalves-Araújo
    • 1
    • 2
  • Ali R. Rajabi-Siahboomi
    • 3
  • Isidoro Caraballo
    • 1
  1. 1.Department of Pharmacy and Pharmaceutical Technology, Faculty of PharmacyUniversity of SevilleSevilleSpain
  2. 2.Department of Pharmacy and Pharmaceutical Technology, Faculty of PharmacyFederal University of CearáFortalezaBrazil
  3. 3.Colorcon Ltd.West PointUSA

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