Nifedipine molecular dispersion in microparticles of ammonio methacrylate copolymer and ethylcellulose binary blends for controlled drug delivery: effect of matrix composition.

The objective of this study is to explore matrix-type microparticles, comprising a solid dispersion of drug with an ammonio methacrylate copolymer and ethylcellulose binary blend, for use in the controlled release of a poorly water-soluble drug, nifedipine. Microparticles consisting of an ethylcellulose N7 (N7) and Eudragit RL (RL) binary blend at different ratios were prepared using phase-separation methodology. The effects of matrix composition on microparticle properties were evaluated by polarized light microscopy, differential scanning calorimetry (DSC), FT-infrared and UV-visible spectroscopy, stability, and drug release studies. Study results indicate that the particle size distribution, particle morphology, and drug release rate from the microparticles were influenced by the ratio of RL to N7. Discrete spherical microparticles with a narrow size distribution and a controlled release profile were obtained when the ratio of RL to N7 was in the range from 1:1 to 2:1 w/w. Solid-state characterization and release kinetic studies on these microparticles confirmed that the nifedipine release from the microparticles followed the Baker and Lonsdale's matrix diffusion model (1974) for microspheres containing dissolved drug, and the nifedipine diffusion in the microparticle matrix was the rate-limiting step. As the ratio of RL to N7 was changed from 0:1 to 4:1 w/w, the effective drug diffusion coefficient in the micro-matrix increased from 5.8 x 10-10 to 8.6 x 10-9 (cm2/h). In addition, probably due to formation of a stable molecular dispersion promoted by hydrogen bonding between nifedipine and the polymers, no significant changes in the nifedipine physical form or release kinetics were observed after 1-year storage at ambient room temperature followed by 3-month accelerated stability at 40 degrees C/75% RH in a closed container.