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

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

•       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 ob_…je_…cti_.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

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