The osmotic-controlled drug release (OROS™) concept for controlling delivery is based on dissolved drug being transported in a controlled manner from the dosage form to the external media under the influence of osmotic pressure. Figure 6.1 illustrates how a solution containing dissolved solute "attracts" water from an adjacent chamber, separated by a semipermeable membrane. Permeation rate depends on
Table 6.1 Selected OROS products
Solubility in water Semipermeable membrane Water-soluble excipients
Antispasmodic Readily soluble Cellulose acetate
Hypromellose, poly(ethylene oxide), sodium chloride, poly(ethylene glycol) (http:// www.rxlist.com/ ditropan-xl-drug. htm)
Calcium antagonist Insoluble Cellulose acetate
Hydroxypropyl methylcellulose, poly(ethylene oxide), sodium chloride, poly(ethylene glycol) (http://www. rxlist.com/ dynacirc-cr-drug. htm)
Covera HS™ Verapamil G.D.Searle Calcium antagonist Soluble
Poly(ethylene oxide), sodium chloride, hydroxyethyl cellulose, hydroxypropyl cellulose, hypromel-lose, poly(ethylene glycol), povidone (http://www.rxlist.com/ covera-hs-drug.htm)
solute concentration ("number of molecules") in the receptor solution. Hence, materials that are ionizable and/or very soluble, and of low molecular mass are the most effective osmotic agents.
If the receptor chamber contains drug and excipients that are osmotically active the hydrostatic or hydraulic pressure exerted by the increased volume of fluid drives ("pushes") drug through one or more orifices in the dosage unit at a relatively constant rate (Fig. 6.2). Such delivery is believed to function independently of environmental conditions in the GI tract (pH, regional location, etc). The technology can be applied to compressed units (tablets) or capsules. The OROS™ concept or variations thereof has been applied to many medicinal agents for delivery in a controlled manner over an extended period of time (Tables 6.1 and 6.2).
Table 6.2 Examples of OROS products with two release ports
Solubility in water Semipermeable
Andrx/Watson Antihyperglycemic Freely soluble Cellulose acetate
Fortamet ER™ Metformin
Andrx/Watson Cholesterol-lowering agent Insoluble Cellulose acetate membrane Excipients
Hypromellose, PEG 4GG, PEG 8GGG, Povidone (http://www.rxlist. com/fortamet-drug. htm)
Hydroxypropyl methylcellulose, hypromellose phthalate, methacrylic acid copolymer, PEG 400, PEG 8000, poly(ethylene oxide), propylene glycol, sodium chloride (http://www.rxlist. com/altocor-drug.htm)
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