The present invention relates to an oral drug delivery system with biphasic release characteristics comprising a porous matrix comprising at least one drug substance, sugar(s), a release retarding polymer, gas generating components and optionally, pharma-ceuti-cally acceptable auxiliary components wherein the pharmaceutical composition further comprises a coating of said drug substance. The pharmaceutical composi-tion, either in the form of pellets (multiparticulate or single unit dosage form), beads, granules, capsules or tablets, is retained in the stomach while selectively delivering the drug(s) at gastrointestinal levels and upper parts of the small intestine over an extended period of time. The release of the drug from the said pharmaceutical composition is characterized by a biphasic release profile of the drug substance, which exhibits both immediate and controlled release characteristics.