Permeability of [ 3H]water across a porous polymer matrix used as rate-limiting shell in compression-coated tablets

Abstract

Compression coating was investigated for use in preparing controlled release dosage forms having a polymer shell surrounding a soluble core. The purpose of the study was to develop a method of measure flux and permeability of water across the outer shell (coat) of the compression-coated tablet. One half of the shell of the press-coated tablets was mounted on the platform of the receptor port of the Thomas diffusion cell by embedment in white petrolatum. The cumulative amount of tritium labeled water per square centimeter permeating across the barrier was plotted vs time, and flux, lag time, diffusion coefficient and permeability were calculated from the steady-state slope. No difference was found whether the outside or inside of the membrane was exposed to the donor phase. The lag time increased linearily and significantly from 0.3 to 0.79 to 1.1 h with increasing shell thickness from 1.08 to 1.66 to 2.12 mm, respectively. Flux and permeability decrease hyperbolically with increasing shell thickness. Increasing hardness at constant shell amount significantly increases lag time and decreases flux and permeability. Compression-coating seems to be a viable technique for preparation of controlled release drug delivery systems with a wide range for adjustment of permeability.