hbs

ASEMINAR ONHYDRODYNAMICALLY BALANCED DRUG DELIVERY SYSTEM : 

ASEMINAR ONHYDRODYNAMICALLY BALANCED DRUG DELIVERY SYSTEM ASHOK KUMAR V 1 M.pharm (Dept. of Pharmaceutics)

H BS : 

H BS The Hydrodynamically balanced drug delivery system, in either capsule or tablet form, is designed to prolong GI residence time of drug in an area of the GI tract to maximize drug reaching its absorption. System is best suited for drugs having a better solubility in acidic environment and having specific site of absorption in the upper part of the small intestine. Gastrointestinal transit time of orally administered dosage forms are controlled by using gastroretentive drug delivery systems (GRDDS).

Need for GRDDS : 

Need for GRDDS A controlled drug delivery system with prolonged residence time in the stomach is of particular interest for drugs which Are locally active in the stomach (misoprostol, antacids antibiotics against H.pylori). Have an absorption window in stomach or in the upper small intestine (L-dopa, P-aminobenzoic acid, furosemide). Are unstable in the intestine or colonic environment (captopril). Exhibit low solubility at high pH values (diazepam, verapamil). Alter normal flora of the colon (antibiotics). Absorbed by transporter mechanism (paclitaxel).

Prolonged gastric retention can be achieved by using various approaches : 

Prolonged gastric retention can be achieved by using various approaches Floating [FDDS] Swelling system Bio/mucoadhesive system High-density systems.

Swelling systems : 

Swelling systems The swelling is usually results from osmotic absorption of water into the dosage form. The dosage form is small enough to be swallowed, and swells in gastric liquids. The whole system is coated by an elastic outer polymeric membrane which is permeable to both drug and body fluids and could control the drug release. The device gradually decreases in volume and rigidity as a result depletion of drug and expanding agent and/or bioreosion of polymer layer, enabling its elimination.

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Prior to administration(A) Drug reservoir (B) Swellable expanding agent (C) and the whole enclosed by elastic outer polymeric envelope. Post administration :Pressure of the expanding agent (B) swelling of the elastic polymer (C). Drug is released from the dosage form through the elastic polymeric envelope.

Mucoadhesive / bio adhesive system : 

Mucoadhesive / bio adhesive system The system involves coating of microcapsules with bioadhesive polymer, which enables them to adhere to intestinal mucosa and remain for longer time period in the GI while the active drug is released from the device matrix. The cationic chitosan polymers are pharmaceutically accepted and used in the preparation of bioadhesive formulations owing to their known ability to bind well to gastric mucosa.

High density systems : 

High density systems Gastric contents have a density close to water (~1.004). A density close to 2.5g cm-3 is necessary for significant prolongation of gastric residence time. The commonly used excipients in high density system includes barium sulphate, zinc oxide, iron powder, and titanium dioxide. The major drawback with such systems is that it is technically difficult to manufacture them with a large amount of drug (>50%) and to achieve the required density of 2.4-2.8g/cm.3

Floating Drug Delivery Systems[FDDS] : 

Floating Drug Delivery Systems[FDDS] Floating drug delivery systems (FDDS) have a bulk density less than gastric fluids and so as to remain buoyant in the stomach. Achieving of the buoyancy retention principle, a minimal level of floating force (F) is also required. F = F buoyancy - F gravity = (Df - Ds) gv--- (1) Where, F= total vertical force, Df = fluid density, Ds = object density, v = volume of the dosage form g = acceleration due to gravity.

Floating Drug Delivery Systems[FDDS] : 

Floating Drug Delivery Systems[FDDS] Single-unit floating dosage system Noneffervescent systems Effervescent (gas-generating) systems Multiple-unit floating dosage system Noneffervescent systems Effervescent (gas-generating) systems Hollow microspheres Raft-forming systems

Effervescent (gas-generating) systems : 

Effervescent (gas-generating) systems Prepared with the help of swellable polymers such as methylcellulose and chitosan and various effervescent compounds, eg, sodium bicarbonate, tartaric acid, and citric acid. On contact with the acidic gastric contents, CO2 is liberated and gets entrapped in swollen hydrocolloids, which provides buoyancy to the dosage forms. The main drawback of single unit dosage systems are high variability of GI transit time when orally administered because of all-or-nothing nature of their gastric emptying.

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(A) Multiple-unit oral floating drug delivery system. (B) Working principle of effervescent floating drug delivery system.

Hollow microspheres : 

Hollow microspheres The techniques involved in preparation include simple solvent evaporation and solvent diffusion and evaporation. The drug release and better floating properties mainly depend on the type of polymer, plasticizer, and solvent employed for the preparation. Hollow microspheres possess the unique advantages of multiple-unit systems and better floating properties as a result of the central hollow space inside the microsphere.

Noneffervescent Systems : 

Noneffervescent Systems These systems contain one or more hydrocolloids and are made into a single unit along with drug and other additives. On contact with water, the hydrocolloids at the surface of the system swell and facilitate floating. The coating forms a viscous barrier, and the inner polymer slowly gets hydrated as well, facilitating the controlled drug release. Such systems are called “hydrodynamically balanced systems (HBS)”.

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It is prepared by incorporating a high level (20%-75% W/V) of one or more gel forming hydrocolloids. Ex; Hydroxy ethylcellulose, Hydroxy propylcellulose, HPMC and Sodium CMC, into the formulation and then compressing these granules into a tablet ( or encapsulating into capsules ). Formulation of these device must comply with the following criteria. It must have sufficient structure to form a cohesive gel barrier. It must maintain an overall specific gravity lower than that of the gastric contains (1.004-1.010). It should dissolve slowly enough to serve as a drug reservoir.

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The gel barrier controls the rate of solvent penetration into the device and the rate of drug release from the device and dosage form remains buoyant in the gastric fluid inside the stomach for upto six hours . Conventional dosage forms disintigrate completely within 60 mins and are emptied totally from the stomach shortly afterward.

Radio activity ,measurement by scintigraphy also showed that the gastric retention was substantially prolonged : 

Radio activity ,measurement by scintigraphy also showed that the gastric retention was substantially prolonged

Potential candidates for FDDS : 

Potential candidates for FDDS Captopril Atenolol Ibuprofen Levodopa Diltiazem Veerapamil Diazepam Amoxycillin trihydrate

Marketted products of FDDS : 

Marketted products of FDDS

REFERENCES : 

REFERENCES 1 .Bardonnet PL, Faivre V, Pugh WJ, Piffaretti JC, Falson F. Gatroretentive dosage forms: Overview and special case of Helicobacter pylori. J Control Release. 2006;111:1-18. 2. Ecyclopedia of Pharmaceutical Technology. 3. Julan UD. Floating Drug Delivery Dystem: An Approach to Gastroretension. Latest Reviews. 2007;5(1). 4.Patil JM , Hirelkar RS ,Gide PS.Trends in floating drug delivery systems.J of scientific and Industrial research.2006,vol 65:11-21. 5.Internet source:www.google.com

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