Models of oral drug delivery

Models of
oral drug delivery

Session Objectives

By the end of this session, students will be able to:

       Explain different models of oral drug
delivery

       Comment mechanism of drug release in various
oral delivery systems

       Apply concepts of microencapsulation techniques
in dosage form development

Different
types of the controlled drug delivery system

1. Dissolution controlled release

A)     Encapsulation
dissolution control

B)      Matrix
dissolution control

2. Diffusion controlled release

A)     Reservoir
Devices

B)      Matrix
Devices

3. Diffusion & dissolution controlled system

4. Osmotically controlled release

C)      Elementary
Osmotic pumps

D)     Push
pull Osmotic Pumps

E)      Controlled
porosity Osmotic pumps

5. Hydrodynamically balanced system

6. pH controlled delivery system

7. Ion exchange controlled delivery system

Dissolution controlled release systems

       Rate
of diffusion from the solid surface to the bulk solution = Rate limiting step

– Flux= (diffusion
coefficient) x (concentration gradient)

J = – D (dc / dx)

OR

Flux = flow rate of
material (dm / dt ) through a unit area ( A )

J = ( 1 / A ) dm / dt

       If
the concentration gradient is linear and thickness of the diffusion layer is h

dc / dx = ( Cb – Cs)
/ h

Combining the above equations:

dm/dt = – ( D A /h
) ( Cb – Cs ) = kA (Cs – Cb)

Types of dissolution models

Two types of dissolution: Controlled, Pulsed delivery
systems

A: Single bead-type device with alternating drug and rate
controlling layer

B: Beads containing drug with differing thickness of
dissolving coats

Matrix dissolution controlled system

       This
systems are called as monoliths

       The
rate of drug availability is controlled by the rate of penetration of the
dissolution fluid into the matrix

       Factors
considered are porosity ,wettability , particle size ,  hydrophobic additives

       Hydrophobic
matrix ex: EC ,polypropylene, polyethylene oxide

       Hydrophilic
matrix ex: MC ,HPMC, NaCMC, HPC

Mechanism of monolithic drug release

       Controlled
dissolution can be achieved by:

1.       Altering
porosity of tablet

2.       Decreasing
its wettability

3.       Dissolving
at slower rate

4.       First
order drug release

       Drug
release determined by dissolution rate of polymer

Examples: Dimetane extencaps, Dimetapp extentabs

Matrix Dissolution Products

Product

Active Ingredients

Manufacturer

Dimetapp  Extentabs 

Brompheniramine

Robins

Donnantal  Extentabs 

…..

Robins

Quinidex  Extentabs 

Quinidine

Robins

Tenuate Dospan

Diethylpropion

Merrel

RESERVOIR DISSOLUTION CONTROL MODEL

1.       Slowly
dissolving substance is used to coat individual particle or granule

2.       Membrane
thickness plays an important role in drug release

3.       Microencapsulation
: Applying a thin coating to solids or liquids, liquids can be effectively
converted into solids by this method

       Micro
encapsulation can be of following types :

1)      Coacervation
phase separation

2)      Interfacial
polymerization

3)      Electrostatic
method

4)      Hot
melt              method

5)      Precipitation
method

6)      Salting
out method

7)      Solvent
evaporation method

Coacervation-phase separation can be done with the:

a)      Formation
of 3 immiscible phases

b)      Deposition
of coating material

c)       Solidification
of coating material

Method

Mechanism involved

Examples

Temperature change

Phase separation of dissolved polymer – immiscible
droplets

Ethyl cellulose & cyclohexane at high temperature

Salt addition

Soluble inorganic salts added

Gelatin- water – sodium sulphate

Non solvent addition

Addition of liquid insoluble in polymer solution

Paracetamol & cellulose acetate

Incompatible polymer

addition

Incompatibility of polymer in the same solvent

Methylene blue –EC- polybutadiene

Polymer-polymer

interaction

Oppositely charged polyelectrolytes — complex  of reduced solubility

Gelatin –acacia – gelatin

 

       Electrostatic method: the drug and coating
material should be in the  form of
aerosols and oppositely charged ; drug and polymer are atomized to  form microcapsules and collected using the
aerosol collecting method

       Interfacial polymerization: dispersion of
organic phase containing drug particles into aqueous phase containing monomers;
where they react at liquid- liquid interface to form a capsule wall, a
crosslinking agent can be added. Low melting solids or poorly soluble organic
liquids

       Precipitation process: the objecti.ve
of this process is to precipitate or congeal a preformed polymer around the
drug being encapsulated.  Eg: sodium
alginate & aq. Calcium chloride solution

       Hot melt technique: at a high temperature
mechanical drop formation is induced with concurrent cooling, the coating for
hot melt technique consist of lipids with low molecular weight. Thermally
stable compound can be only  used

       Salting out method: an aqueous polymer
solution is prepared to which  salt is
added leading to the separation of the polymer solution , high level of  the salt concentration into capsule shell

       Solvent evaporation method : the drug and
capsule wall forming  material are
solubilized in organic volatile solvents immiscible with water , an  emulsion is formed by dispersion into aqueous
solution , solid micro capsules  are
formed after solvent evaporation

Product

Active
Ingred

Manufacturer

Ornade Spansules

PPA, chlorphen.

SKB 

Contact

PPA, others

SKB 

Diamox Sequels

Acetazolamide

Lederle(WA)

Chlor-Trimeton  Repetabs

Chlorphen

Schering

 

Summary

  • Different
    types of controlled release systems are: 
    Dissolution system, Diffusion system, Dissolution &
    diffusion  system, Osmotic regulated
    system, pH regulated system, Ion 
    exchange controlled systems and Hydrodnynamically  balanced systems

  • Types
    of dissolution models are controlled and pulsed delivery systems. The drug
    release from dissolution controlled delivery  systems are dependent upon porosity
    ,wettability ,particle size  &
    hydrophobic additives in the formulation

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