A tablet consisting of two layers of swelling and rupturable coatings was prepared and evaluated as pulsatile drug delivery system. Aceclofenac was used as model drug. The tablets were prepared by direct compression method. Different ratio of spray-dried lactose and microcrystalline cellulose were then coated sequentially with an inner swelling layer containing a superdisintegrant (croscarmellosesodium) and an outer rupturable layer of ethyl cellulose. The effect of spray-dried lactose and microcrystalline cellulose on swelling layer and rupturable coating was investigated. In vitro dissolution was preformed using the USP paddle (type II) apparatus at speed of 50 rpm by using phosphate buffer pH 7.4 as a dissolution medium. The lag time of the pulsatile tablets of Aceclofenac decreased with increasing concentration of microcrystalline cellulose in the cores and increased with increasing levels of both swelling layer and ruputable ethyl cellulose coating. Increasing levels of water uptake by the ethyl cellulose coating causes bulging and become like gel and forms insoluble skeleton where the drug seems to be timecontrolled release, and thus prolonged the lag time.
