title: Drug Release from Inert Spherical Matrix Systems Using Monte Carlo Simulations.
abstract: BACKGROUND
  Computational approaches for predicting release properties from matrix devices have recently been purposed as an approach to better understand and predict such systems. The objective of this research is to study the behavior of drug delivery from inert spherical matrix systems of different size by means of computer simulation.
  
  
  METHODS
  To simulate the matrix medium, a simple cubic lattice was used, which was sectioned to make a spherical macroscopic system. The sites within the system were randomly occupied by drug-particles or excipient-particles in accordance with chosen drug/excipient ratios. Then, the drug was released from the matrix system simulating a diffusion process.
  
  
  RESULTS
  When the released fraction was processed until 90% release, the Weibull equation suitably expressed the release profiles. On the basis of the analysis of release equations, it was found that close to the percolation threshold an anomalous released occurs, while in the systems with an initial drug load greater than 0.45, the released was Fickian type. It was also possible to determine the amount of drug trapped in the matrix, which was found to be a function of the initial drug load. The relationship between the two mentioned variables was adequately described by a model that involves the error function. Based on the these results and by means of a non-linear regression to the previous model, it was possible to determine the drug percolation threshold in these matrix devices.
  
  
  CONCLUSIONS
  It was found that the percolation threshold is consistent with the value predicted by the percolation theory.
authors.affiliation: División de Estudios de Posgrado (Tecnología Farmacéutica), Facultad de Estudios Superiores Cuautitlán/ UNAM, Av. Primero de Mayo S/N, Cuautitlán Izcalli 54740, Estado de México, Mexico.
authors.forename: Rafael
authors.initials: R
authors.lastname: Villalobos
authors.forename: Erika V
authors.initials: EV
authors.lastname: Garcia
authors.forename: David
authors.initials: D
authors.lastname: Quintanar
authors.forename: Paul M
authors.initials: PM
authors.lastname: Young
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004058:Diffusion; D065546:Drug Liberation; D009010:Monte Carlo Method; D010316:Particle Size; D004364:Pharmaceutical Preparations / Q000737:chemistry*
chemical_list: D004364:Pharmaceutical Preparations
keywords: Drug controlled release; fractal dimension; in silico simulation; modelling; percolation theory; percolation threshold; spherical matrix systems