Dissolution from Ethylene Vinyl Acetate Copolymer Long-Acting Implants: Effect of Model Active Ingredient Size and Shape

In recent pharmaceutical applications, an active pharmaceutical ingredient (API) can be mixed with a polymer material to yield a composite long-acting drug-delivery device. These devices boast higher patient compliance, localized drug delivery, and lower dosage concentrations, which can increase patient safety. As a laboratory-safe option, calcium carbonate (CaCO₃) was used as a drug surrogate to mimic the release kinetics of a low-solubility API. The release of CaCO₃ from a poly(ethylene vinyl acetate) (EVA) polymer matrix was studied in ultra-high-purity water. The geometry of CaCO_3, along with the manufacturing technique, was manipulated to study the implications on surrogate drug release. It was found that injection molding proved to yield higher burst release, due to higher pressures achievable during manufacturing. The extrusion process can affect the surface concentration of the pharmaceutical ingredient when extruded through a water bath, resulting in a lower initial burst concentration. Regarding CaCO₃ geometry, the particle size was more critical than the surface area in terms of CaCO₃ release. Larger particles showed a higher release rate, though they also displayed higher variability in release. These data can be used to engineer specific release profiles when designing composite formulations and manufacturing methods for pharmaceutical-drug-delivery applications.