Peroral drug delivery system

PCT No. PCT/FI92/00274 Sec. 371 Date May 5, 1994 Sec. 102(e) Date May 5, 1994 PCT Filed Oct. 15, 1992 PCT Pub. No. WO93/07858 PCT Pub. Date Apr. 29, 1993.This invention describes a device for peroral administration of a therapeutic agent which is capable of existing in an unionized therapeutically active form. The device comprises a reservoir comprising the therapeutic agent in ionized form, which reservoir has a wall permeable to un-ionized material and impermeable to ionized material; and a solid material which upon uptake of water is converted to a buffer; the solid material having, on uptake of water, a pH which determines the rate of permeation of the therapeutic agent in un-ionized form through the reservoir wall. The device enables the release of the therapeutic agent to be controlled by the pH of the buffer and, if desired, the composition of the reservoir walls. The composition of the surrounding aqueous medium does not affect the rate of release.