a once - a - day controlled release drug delivery system of diltiazem hydrochloride is provided , which is bioequivalent in plasma profile of cardizem cd . the fast , medium , and slow release fractions are prepared using various compositions and weight gains . the individual fill weights are computed and then are filled into the same capsule using specialized encapsulation equipment using a triple - filling process . a preferred membrane dispersion that is used for preparing the fast release fraction contains 0 . 2 % of sodium lauryl sulfate along with 20 % of water soluble plasticizer , and 2 % silicone dioxide , based on quaternary polymethacrylate on the weight basis . this combination provides an initial pulsatile burst after a lag time of 2 hours , leading to in - vivo bioequivalence . the preferred membrane dispersion that is used for preparing the medium release and the slow release fractions contain 16 % of water soluble plasticizer along with 5 % silicone dioxide , based on quaternary polymethacrylate . this combination provides an optimal glass transition temperature that allows for the preparation of exceptionally increased weight gains . additionally , it provides targeted input of drug release for achieving bioequivalence . regardless of significant in - vitro inequivalence to the release rate profile of the innovator product , the in vivo - equivalence data comply with required regulatory guidelines .