Matrix type controlled release systems: I. Effect of percolation on drug dissolution kinetics

Area of Science:

• Pharmaceutical Sciences
• Materials Science
• Chemical Engineering

Background:

• Controlled drug release systems are crucial for therapeutic efficacy.
• Understanding drug release mechanisms from matrix tablets is essential for formulation design.
• Ethyl cellulose is a common matrix material for sustained drug delivery.

Purpose of the Study:

• To investigate the drug release kinetics of caffeine from ethyl cellulose matrix tablets.
• To apply percolation theory to explain drug release across a wide range of drug loadings.
• To determine the critical porosity and its relation to drug content.

Main Methods:

• Preparation of matrix tablets by compressing binary mixtures of caffeine and ethyl cellulose.
• Varying drug content from 10% to 100% (w/w).
• Studying drug dissolution from a single flat side and applying percolation theory.

Main Results:

• Drug release kinetics were explained by percolation theory over the entire drug loading range.
• Incomplete release observed below the lower percolation threshold due to encapsulation.
• Matrix-controlled release observed between percolation thresholds, with zero-order kinetics at high loadings.
• A scaling law for the diffusion coefficient near the percolation threshold was identified.

Conclusions:

• Percolation theory effectively models drug release from ethyl cellulose matrix tablets.
• The lower percolation threshold (critical porosity) was determined to be 0.35, corresponding to approximately 28% drug content.
• This provides a predictive model for designing controlled-release formulations.