The present invention relates to an oral osmotic system for the control and continuous administration of metoprolol over a lengthy time interval, which contains a uniform, separate internal layer of water-soluble coating agent. Water-soluble coating agents which can be used are HPMC, PVP, optionally mixed with polyethylene glycol.

The system having improved formulation properties such as hardness and resistance to breakage consists of a) an outer shell composed of a semipermeable material which is permeable to water and impermeable to the components of the core which contains the active ingredient b) a core with a mixture which is sufficiently soluble in water to generate osmotic pressure and is composed of about 7.5 to about 15 % by weight of poly-N-vinylpyrrolidone about 5 % by weight of a glidant or lubricant customary...