The present invention is concerned with a multi-layer sustained release dosage form for use in the oral cavity. More specifically, the invention includes a portion or layer which contains an active substance, this portion or layer hereafter referred to as a drug reservoir, and a drug release controlling layer which is formed with a non-saliva dissolving polymer. The drug reservoir and the drug release controlling layer are formed over an adhesive layer, the latter adhering to oral cavity tissue. If desirable, a drug impermeable layer is formed between the drug reservoir and the adhesive layer. The dosage form of the present invention sticks to the oral tissue, and releases the drug continuously over a long period at a constant rate, with saliva permeating through the drug release controlling layer. The drug action is sustained with the drug being absorbed from the oral cavity via, for example, an oral cavity tissue such as a mucosal membrane.
Although oral administration and injection are currently the main administration routes for drug therapy, a safer and more effective administration route and device is desirable for various reasons. The oral cavity tissue, including the mucosal membrane is one of the few possible administration sites, and there have been numerous reports on this possibility. One example is sublingual tablets. Such tablets can be used for a drug whose quick action is desirable, such as nitroglycerin, but the tablets cannot be retained under the tongue for a long period of time. Drug action in the oral cavity can be relatively prolonged using buccal tablets, and sustained action can be achieved by changing the disintegration time of the tablets. However, the disintegration time varies with the administration method and also from one subject to another. Although buccal tablets have been reported, see, for example, Tokkaisho 58-213709, even with these dosage forms drugs can be released into the oral cavity quantitatively for a long period of time for a prolonged constant drug absorption.