AbstractA new type of complex reservoir–matrix system for the controlled delivery of diltiazen hydrochloride was developed. This capsule‐type device was designed for oral administration to humans and/or animals. It contained (i) an appropriate amount of the drug in a compartment; (ii) a swelling‐controlled membrane which was prepared by mixing polymeric materials with another appropriate amount of the drug; and (iii) a water‐soluble gelatin capsule as container. The swelling‐controlled membranes were prepared from poly(2‐hydroxyethyl methacrylate) hydrogels. The effect of pH on the swelling of the hydrogels was studied. In‐vitro dissolution testing was carried out to evaluate the release of the drug using a continuous‐flow method. Zero‐order release kinetics was obtained over a period of 12 h.