Classification enters the system and activate it .On

Classification
of Osmotic DDS

Osmotic Drug Delivery Devices fall in two categories:

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·        
Implantable:

1       Implantable osmotic pump

2      
Oral osmotic Pump

 

 

 

 

 

 

1.Implantable osmotic pump

 

 

 

2 Oral osmotic pump

A )Single chamber osmotic pump: 

B).Multi chamber osmotic pump

 

C) Modified osmotic pump

 

1. Oral osmotic pump

A. the Rose and Nelson pump:

Origin:

  This drug delivery system was first time
designed by the Australian scientists Rose and Nelson, in 1955 when they were
administering drug into the sheep and cattle gut

Components

           This drug delivery device consists of three
chambers

               1 .Drug chamber

2.    
Salt chamber holding salt bridge

3.    
Water chamber

4.
Semi permeable membrane

Working

       Semipermeable divides the salt and water chamber
as the water enters from water to salt chamber due to gradient development by
osmotic pressure the salt chamber extends and forces the drug chamber . Drug
coms out of the orifice and finally pumped from the DDS to the targeted area.

B. Higuchi Leeper osmotic
pump

              This DDS is the advancement
of Rose and Nelson pump, in its components in a way that it has no water
chamber.

Components

1       Salt
chamber

2       Drug
chamber

3       Semi
permeable membrane

4       A rigid
housing

Working

    As is has no water chamber so through the
process of imbibition drug enters the system and activate it .On implantation
of device the biological fluid present in the surroundings enters the salt
chamber which contains the fluid solution , on entering biological fluid
absorbs MgSO4 and build up a osmotic pressure that in turn forces the movable
partition towards drug chamber and drug comes out of the orifice

Modification

Through
this system pulsatile delivery is accomplished . Pressure is the critical factor
.This is done by drilling the orifice with stretching elastic material upto the
specific concentration pressure build up open the orifice and drug is delivered
again after drug release pressure declines and orifice get closed.

Application:

This
system is employed in veterinary for administration of antibiotics and growth
hormones in animals.

C. Highuchi Theeuwes
osmotic pump

 This drug delivery system is a further
advancement of Rose and Nelson pump in 1970 .This system is different in
working with respect to previous one in a way that semi permeable membrane is
present in rigid housing.

Components

1. Salt chamber

2. Drug chamber

3. Rigid housing

4. Semipermeable membrane

Working

         This device also works on imbibition of water
into system here membrane is strong enough to withstand high pressure. Drug is
loaded just before the application in this way this device is used for longer
period of time giving the extended release. Drug delivery is governed by the
salt in the salt chamber and permeability features of the cell membrane.

D. Implantable mini-osmotic
pumps

     Osmotic pump working on this system was Azlet
pump designed by Azlet Corporation in 1976. They are small and compact mini-osmotic
pumps.

Application

  For implantable in –vivo controlled studies
where continuous drug is required. For the loss of drug by diffusion delivery
port is designed in a longitudinal position  

 

2. Single chamber osmotic pump:

Elementary osmotic pump:

    New drug delivery device, basic Oros system
was described by Theeuwes in 1975. It is a major controlled rate device.

Components

1.    
Laser drilled semi permeable membrane

2.    
Osmotic core

Working

   Control is present inside the water that
surrounds the formulating agent. Tablet comprises of osmotic core having drug
and laser drilled holes semi permeable membrane. On administration water
penetrates into the system and drug dissolution occurs and the drug solution is
released in a controlled manner at constant rate by osmosis .This replaced the
drug in the core and drug is released from orifice . This DDS promotes zero
order reaction.

Drawback

Only
suitable for water soluble drugs

 

Multi chamber osmotic pump:

Push pull osmotic pump:

  It is a modification of EOP, used for poorly
water soluble and water soluble drugs at a steady rate; resemblance with bi-layered
coated tablet.

Components

1.    
Two layers ( functionally different)

2.    
Semi permeable

Working

   Upper layer has drug osmogen, second layer
consists of polymeric agent, coloring agents and excipients then tablet is
surrounded by laser drilled holes. Polymeric system will form a suspension of
drug in situ. When the system comes across with GIT fluid the polymeric osmotic
layer swells up and delivers the drug to the external environment .via orifice
in a fine dispersion

 

Osmotic pump with non-expanding
second chamber

It
is further classified into two types.

Components

1.    
Two layers

2.    
Porous semi permeable membrane.

Working  

   In the
first type, second chamber aids in dilution of drug solution

 This is beneficial because some drugs cause
the irritation when they are saturated.

In second type, there are
two chambers, one comprises of the osmotic agent and the other comprises of the
drug. Osmotic agent solution is formed which enters the drug solution and then
their mixture is pumped out by means of semipermeable membrane present surrounding
the chamber.

Specific types

Controlled porosity osmotic
pump

Components

1.     Laser drilled Semi permeable
membrane

2.     Two layers

Working
It is an osmotic device wherein the
delivery holes are molded in situ through leaching of water soluble
pore-forming agents merged in semipermeable membrane (E.g., urea, nicotinamide,
sorbitol, etc.). Drug release rate from controlled porosity osmotic pump relies
on various factors like coating thickness, level of leachable pore-forming
agent(s) solubility of drug in tablet core, and the osmotic pressure difference.

Advantage

  Lessen the stomach irritation, as drug
is released from the whole of the device surface instead of from a single hole.
Moreover, no complex laser-drilling unit is necessary because the delivery
orifices are designed in situ

 

Osmotic bursting osmotic pump:

This system is for provide pulsatile release

Modification

This system has resemblance to an elementary osmotic pump instead
delivery orifice is absent and size is smaller. When it is placed in an gastric
fluids, water is absorbs and hydraulic pressure is developed inside so that the
semipermeable membrane rupture and the drug is released to the environment. By
changing the thickness as well as the area of semipermeable membrane can be
regulated and in return release of drug.

 

 

 Liquid Oral Osmotic system:

This system is used for liquid drug formulations. A liquid formulation
is specifically suitable for delivering insoluble drugs and macromolecules such
as polysaccharides and polypeptides. Molecules require external liquid
components to assist in solubilization, dispersion, protection from enzymatic
degradation, and promotion of gastrointestinal absorption.

COMPONENTS

1.    3 layers

2.    Semipermeable
membrane

3.    Soft gelatin capsule

 

Working

This device containing three- layers first is rate controlling membrane,
second is osmotic layer and third is soft gelatin capsule. During process,
water permeates across the rate controlling membrane and causes increase of the
osmotic layer resulting in to development of hydrostatic pressure in the system
which expels the liquid formulation out of the delivery orifice.

 

Sandwiched osmotic tablet (SOT)

Components

1.    
2
layers

2.    
Semi
permeable membrane

Working

       Polymeric push layer sandwiched between
two drug layers with two delivery holes. When placed in the aqueous
environment, the middle push layer containing the swelling agents’ swells and
the drug is delivered from the two orifices located on opposite sides of the
tablet.

Advantage

1.    
To avoid local irritation of
stomach.

 

Delayed Delivery Osmotic device:

            Because of semi
permeable walls, an osmotic device fundamentally show lag time before drug
delivery begins. No doubt this characteristic is usually considered as a disadvantage,
it can be used beneficially. The delayed release of certain drug (drugs for
early morning asthma or arthritis) may be helpful.

 Telescopic Capsule for Delayed Release:

  Components

1.    
Two
chambers

2.    
Exit
port

3.    
Waxy
separation

4.    
Semipermeable
membrane

Working

This device comprises of two chambers, the first chamber has drug and an
exit port, and the second consists of an osmotic engine .A layer of wax like
material act as partition in between two layers. To join the delivery device,
the active agent is sited into one of the sections by manual or mechanical fill
process. The bilayer tablet with the osmotic engine is put into a completed cap
part of the capsule with the convex osmotic layer projected in to the closed
end of the cap and the barrier into the closed end of the cap and the barrier
layer uncovered towards the cap opening. The open end of the filled vessel is
fitted into the open end of the cap, and the two pieces are pressed together
until the cap, osmotic bilayer tablet and vessel fit together firmly. When
fluid is absorbed in the device, the osmotic engine swells and exerts pressure
on the movable connected first and second wall sections. During the delay
period the volume of reservoir containing the active agent is kept continuous
and steady, therefore a slight pressure gradient exists between the environment
of use and internal side of the reservoir. As a result, the flow of
environmental fluid compelled by the pressure enter the reservoir is minimal
and subsequently no agent is carried for the period 

 

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