Dual drug dosage forms with improved separation of drugs

A method for the manufacture of a pharmaceutical tablet which upon oral ingestion delivers a first drug by immediate release and a second drug by prolonged release defined as a release rate into gastrointestinal fluid that is slow enough to leave at least about 40% of said second drug unreleased one hour after ingestion, said method comprising:

• (a) dispersing said second drug in a solid matrix to form a unitary body which upon immersion in gastrointestinal fluid releases said second drug by prolonged release, wherein said solid matrix comprises a first polymer wherein said matrix (i) swells upon imbibition of fluid to a size that promotes retention of the dosage form in a stomach;
• (ii) releases substantially all of said second drug within about 10 hours upon immersion of the dosage form in fluid;
• and (iii) remains substantially intact until substantially all of said second drug is released;
• (b) depositing on a surface of said unitary body a polymeric film that is devoid of said first drug and said second drug, wherein said polymeric film adheres to a surface of said solid matrix and wherein said polymeric film comprises a second polymer having a molecular weight which is lower than the molecular weight of said first polymer and is dissolved in gastrointestinal fluid upon ingestion, wherein the ratio of said polymeric film to unitary body is from about 0.005:1 to about 0.2:1;
• (c) depositing over said polymeric film a fluid medium comprising said first drug and a liquid carrier that does not remove said polymeric film upon contact therewith;
• and
• (d) evaporating said liquid carrier from said fluid medium thus deposited to leave a solid layer containing said first drug over said unitary body, wherein said solid layer adheres to said polymeric film, and wherein said solid layer provides immediate release of said first drug upon immersion of the dosage form in fluid.