Which statement best distinguishes diffusion-controlled release in polymeric matrices from erosion-controlled release?

• A. Diffusion-controlled release is governed by Fickian diffusion of drug through a porous or swollen matrix.
• B. Erosion-controlled release results from polymer degradation (mass loss) releasing drug.
• C. Diffusion-controlled release cannot occur in swollen matrices.
• D. Erosion-controlled release is driven by diffusion through intact polymer.

Answer: (B)

Diffusion-controlled release involves drug molecules moving through the polymer matrix, often governed by Fickian diffusion, and can occur when the matrix is porous or swollen with water. Erosion-controlled release, on the other hand, happens when the polymer itself degrades and loses mass, physically releasing the drug as the matrix breaks down. This degradation-driven mechanism is what clearly distinguishes erosion-controlled release from diffusion-controlled release, because it shifts the release driver from molecular diffusion through the matrix to the rate of polymer degradation. The other statements misrepresent either diffusion behavior in swollen matrices or the mechanism of erosion, which is not driven by diffusion through an intact polymer.