Oros osmotic pump

In parenteral therapy, the subcutaneously implantable, osmotic mini-pumps developed by the Alza Corp. are used widely in experimental animal studies. The DUROS implant pump is a modified version of the Alzet pumps and was developed specifically for the controlled delivery of peptides and proteins (see Section 4.6.1.2). Osmotic mini-pumps, such as the Oros osmotic pump, are also available for controlled... 

The simplest osmotic dosage form, ALZA Corporation s OROS elementary osmotic pump (Fig. 7), combines the dmg and sometimes an osmotic agent in a monolithic core and deflvers the dmg in solution (102). The mass dehvery rate with time dm df) of the dmg solution is described by equation 4, where is the hydrauHc permeabiUty of the membrane, a is the membrane reflection coefficient, Atz is the osmotic pressure gradient, APis the hydrostatic back pressure, A is the area of the membrane, C is the dissolved concentration of the dmg, and b is the membrane thickness. 

Osmotic Control. Several oral osmotic systems (OROS) have been developed by the Alza Corporation to allow controUed deHvery of highly water-soluble dmgs. The elementary osmotic pump (94) consists of an osmotic core containing dmg surrounded by a semi-permeable membrane having a laser-drilled deHvery orifice. The system looks like a conventional tablet, yet the outer layer allows only the diffusion of water into the core of the unit. The rate of water diffusion into the system is controUed by the membrane s permeabUity to water and by the osmotic activity of the core. Because the membrane does not expand as water is absorbed, the dmg solution must leave the interior of the tablet through the smaU orifice at the same rate that water enters by osmosis. The osmotic driving force is constant until aU of the dmg is dissolved thus, the osmotic system maintains a constant deHvery rate of dmg until the time of complete dissolution of the dmg. 

The invention that positioned osmosis as a major driving force for controlled drug delivery was the elementary osmotic delivery system. ALZA has developed elementary osmotic delivery systems under the name OROS. A successful modification that overcame the disadvantages of the elementary osmotic pump was the Push-Pull osmotic drug delivery system. The following sections are devoted to the principal features of these systems. 

Elementary osmotic pump (EOP). OROS represents the oral osmotically... 

OROS Push-Pull system. After the introduction of commercial products based on EOP technology in the early 1980s, numerous attempts were made to apply the osmotic concept to a broader range of drugs. Since the elementary osmotic pump is limited to the delivery of relatively soluble drugs with solubilities greater than about 2 to 10 wt%, depending on dose, other modifications were necessary to expand the utility of the EOP... 

FIGURE 6.39 Effect of pH and stirring on the release of KC1 from elementary osmotic pump tablets (OROS ). [Graph reconstructed from data by F. Theeuwes, J. Pharm. Sci., 64, 1987 (1975).]... 

OROS hydromorphone utilizes the patented Push-Pull osmotic pump technology which provides a steady and continuous release of drug over 24 hours, thus providing consistent drug plasma levels and... 

In the OROS system, solid drug—present alone or with an osmotic driving agent—is surrounded by a semipermeable membrane having one delivery orifice (Figure 9). During pump operation, water from the environment is continuously imbibed across the semipermeable membrane, by osmosis, to produce the fluid drug formulation. The membrane s structure does not allow expansion of the tablet s volume ... 

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