Mechanism Of Drug Delivery System Of
Sustained & Controlled Release Tablet

Presented by: Submitted to:

Himanshu Shahu Dr. Kanchan Kohli

M.Pharm (1st sem) Dept. of Pharmaceutics

School Of Pharmaceutical Education And Research (SPER), Jamia Hamdard 1

MECHANISM OF RELEASE OF DOSAGE:

1. Dissolution controlled system:

• Easy to design

• Formulated by slowing dissolution rate of drug in GIT through incorporating it into an insoluble polymer

and coating with diff. material of varying thickness.

• Rate limiting step in such DDS is diffusion of drug across boundary layer.

The rate of dissolution is given by following equation

dm/dt = ADS/h

Where, S= aq. Solubility of drug

A=surface area of tablet

D=Diffusivity of drug

h= thickness of boundary layer
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MECHANISM OF RELEASE OF DOSAGE:

 Dissolution control can be achieved in following ways:

• Slow dissolution of drug

• Drug with inherently slow dissolution rate.

• Drugs that transforms into a slow dissolving form.

• Slow dissolution rate of reservoir membrane & matrix

• Embedment in slowly dissolving, degrading erodible matrix. Encapsulation or coating with

slowly dissolving degrading erodible substances.

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MECHANISM OF RELEASE OF DOSAGE:

 Types of dissolution Controlled System:

1. Matrix dissolution Controlled System:

• it consists of a drug mixed with a polymer such as bees wax or carnuba wax and from

which the drug is then released slowly depending upon the porosity of the tablets.

2. Reservoir dissolution Controlled System

• In this type the drug is coated with polymer material such as Cellulose and PEG and the

release of drug depends upon solubility and thickness of coating.

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MECHANISM OF RELEASE OF DOSAGE:
2. Diffusion Controlled System:

• In this system the rate controlling step is diffusion of the drug

across the physical barrier.

• This system always follows first order kinetics

• This DDS can be prepared either by encapsulating the drug in polymer or dispersing the drug in the

matrix

The rate of diffusion is given by following equation:

dm/dt = ADK∆C/l

Where, K= Partition co-efficient of drug between drug core and membrane

A= surface area of tablet

D= Diffusion co efficient

l= Diffusion path length 5

∆C= Concentration difference across membrane

MECHANISM OF RELEASE OF DOSAGE:

 Types of diffusion Controlled System:

• Porous matrix controlled system:

Rate controlling element is water swellable material.

e.g. xanthan gums, guar gum, high viscosity grades of HPMC, HPC, alginates

• Porous membrane controlled system:

Rate controlling element is non-swellable water insoluble polymer.

Drug release controlled through micropores.

e.g. ethyl cellulose, PMA.

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MECHANISM OF RELEASE OF DOSAGE:

3. Osmotic Pressure Controlled System:
• Provides zero order release

• Drug may be osmotically active, or combined with an osmotically active salt (e.g., NaCl).

• Semipermeable membrane usually made from cellulose acetate.

• More suitable for hydrophilic drug.

Examples: Glucotrol XL, Procardia XL.

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MECHANISM OF RELEASE OF DOSAGE:

4. Water penetration (swelling):

• This type of systems are initially dry and when placed in body, absorb water or other fluid

and it swells.

•Swelling increases aq. solvent content within the formulation as well as the polymer mesh

size, enabling the drug to diffuse through the swollen network into external environment.

E.g. (N-isopropylacrylamide), Ethylene-vinyl alcohol

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REFERENCE:

Leon Lachman- The theory and practice of industrial
pharmacy.

N.K. Jain- Controlled and novel drug delivery system.

Brahmankar- Text book of Biopharmaceutics and
Pharmacokinetics.

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THANKYOU!

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