In this system a semipermeable membrane around a core of an osmotically active drug or a core of an osmotically inactive drug in combination with an osmotically active salt. The drug either in the from of solid or as solution.
Semipermiable housing having controlled water permeability,the drug is activated to release in solution form at a constant rate through a special delivery orifice.
If the drug is solution so the intrinsic rate of drug release Q/t is given by:
Q/t = Pw Am /hm (πs-πe )
If the drug is solid so the intrinsic rate of drug release Q/t is given by:
Q/t = Pw Am /hm (πs-πe)Sd where, Pw = water permeability, Am = effective surface area, hm = thickness of the semipermiable housing, (πs-πe)=deferential osmotic pressure b/w drug delivery system and external environment, Sd=aqueous solubility of the drug contained in solid formulation.
This type of osmotic pump consists of 2 layers of membrane.
The inner is microporous membrane, which is made up of cellulosic material containing some pore forming agents, covered by a semipermeable membrane.
When the system is placed in an aqueous environment the soluble components of first layer of coating dissolve, resulting in a microporous membrane, which provides greater flux of water into the system.
When it is placed in an aqueous environment, water is imbibed and hydraulic pressure is built up inside until the wall ruptures and the contents are released to the environment.
Varying the thickness as well as the area the semipermeable membrane can control release of drug. This system is useful to provide pulsated drug release.
Sandwiched osmotic tablets
It is composed of polymeric push layer sandwiched between two drug layers with two delivery orifices.
When placed in the aqueous environment the middle push layer containing the swelling agents swells and the drug is released from the two orifices situated on opposite sides of the tablet and thus SOTS can be suitable for drugs prone to cause local irritation of the gastric mucosa.
Hydrodynamically balanced system are also known as floating drug delivery system.
In this system the reservoir is homogenously dispersed in a swellable polymer matrix fabricated from a hydrophilic polymer.
In GIT the laminate absorbs GI fluids & become increasingly swollen, which generate hydrodynamic pressure in the system,the hydrodynamic pressure thus created forces the drug reservior compartment to reduce in volume and causes the liquid drug formulation to release through the delivery orifice at a rate defined by :-
Hydrodynamic pressure activated drug delivery system can be fabricated by enclosing a collapsible, impermeable container, which contains a liquid drug formulation to form a drug reservoir compartment.
Inside a rigid shape retaining housing a composite laminate of an absorbent layer and a swellable hydrophilic polymer layer is sandwiched between the drug reservoir compartment and the rigid housing.
Gel forming hydrocolloids swells in contact with gastric fluid after oral administration and maintains a relative integrity of shape and a bulk density of less than unity within gastric environment. The air thus trapped by the swollen polymer imparts buoyancy to the dosage form.
The gel barrier controls the rate of solvent penetration into the device & the rate of drug release from the device.
It maintains a bulk density of <1 and thus remains buoyant in the gastric fluid inside the stomach for upto 6 hrs; conventional dosage forms disintegrate completely within 60 min and are emptied totally from the stomach shortly afterward.
Advantages of HBS
Delivery of drugs for local action in stomach.
Minimizing the mucosal irritation due to drugs, by drug releasing slowly at controlled rate
This type of activation controlled drug delivery system permits targeting the delivery of drug only in the region with the selected pH range.
Drugs administered orally would encounter a spectrum of pH ranging from 7 in the mouth, 1 - 4 in the stomach and 5 - 7 in the intestine.
Prepared by first blending an acidic or basic drug with one or more buffering agents (Eg. primary, secondary, tertiary salt of citric acid) granulating with appropriate pharmaceutical excipients to form small granules and then coating the granules with a gastrointestinal fluid permeable film forming polymer (Cellulose derivatives).
The polymer coating controls the permeation of gastrointestinal fluid. The gastrointestinal fluid permeating into the device is adjusted by the buffering agents to an appropriate constant pH, at which the drug dissolves and is delivered through the membrane at a constant rate regardless of the location of the device in the alimentary canal.
It is also fabricated by coating the drug containing core with a pH sensitive polymer combination
For instance, a gastric fluid labile drug is protected by encapsulating it inside a polymer membrane that resists the degradative action of gastric pH, such as the combination of ethyl cellulose and hydroxyl methyl cellulose phthalate.
In the stomach, coating membrane resists the action of gastric fluid (pH<3) & the drug molecule is thus protected from acid degradation.
After gastric emptying the drug delivery system travels to the small intestine and the intestinal fluid solubulize the hydroxyl methyl cellulose phthalate component from the coating membrane.
This leaves a microporous membrane of intestinal fluid insoluble polymer of Ethylcellulose, which controls the release of drug from the core tablet.
The drug solute is thus delivered at a controlled manner in the intestine by a combination of drug dissolution and pore channel diffusion.
ION EXCHANGE RESINATES AS CONTROL DRUG DELIVERY SYSTEM
Principle A Cation exchange resin generally has Sulphonic and Carboxylic functional groups as an integral part of the resin and an equivalent amount of cationic drug molecules. An Anion exchange resin generally has quaternary ammonium groups and polyalkylamine functional groups as an integral part of the resin and an equivalent amount of anionic drug molecules.
General preparation of drug resinates Column process: A highly concentrated drug solution is eluted through a bed or column of the resin until equilibrium is established. Batch process: The resin particles are stirred with a large volume of concentrated drug solution.