§ osmotic delivery on the other hand, most

§  Semi-permeable membrane : §  Criteria 1.    
Adequately wet strength and  permeability.
2.     Should be non
toxic and inflexible. 3.     Should be
adequately thick to withstand the pressure of device. 4.    
Any which  is spongy  to water but impermeable to solute can be used as a coating substance .e.g.; Cellulose acetate,
cellulose triacetate and ethyl
cellulose. §  Hydrophilic polymers :  CMC, HPMC
, HEC §  Wicking agent : SLS , PYP , Bentonite § 
Solubilizing agent : PVP ,CP , PEG §  Osmogens : Nacl , KCl § 
Plasticizer : Phathaltes , benzoates , TEC §  Flux regulator :
Polypropylene , polybutylene §  Pore forming agent : Calcium nitrate , Potassium sulphate §  Coating
solvent : acetone and methanol
(80:20) , acetone and water (90:10) §  Surfactants : poly oxyethylenated
castor oil Factors that affect
the drug release from osmotic
delivery of drugs:
                           The drug delivery  from
osmotic delivery device rely
on various process and formulation aspects . Apart from the water miscibility of the drug, the solubility of the further fundamental
ingredients can also have main  impact on the drug delivery by producing an osmotic pressure gradient crosswise  the
polymeric layer on interaction with dissolution medium. The rate of drug release from osmotic pumps rely on the total solubility and the
osmotic pressure of the drug. Many features  that
influence the release of drug from osmotic system are follows:  Orifice Size: 
              
Osmotic drug delivery apparatus  comprises of at least one delivery orifice in the semipermeable membrane for drug delivery
and the diameter of delivery orifice   should be optimized in
order to regulate the drug release from osmotic
systems . To obtain an suitable  zero-order delivery profile, the area of the orifice should  be reduced
than a size Smax to minimum drug
delivery by diffusion through orifice. Moreover, the area must be adequately large, above
a minimum size Smin, to lessen the hydrostatic pressure build up in the device. Else, the hydrostatic pressure can break the membrane and influences the zero-order release rate of drug. Therefore, the cross sectional area of the orifice must be maintained between minimum and
maximum values.  Solubility:
             The delivery
rates of drug rely on the solubility of
the solute inside the drug delivery device. Subsequently, drugs should have adequate solubility to be delivered by osmotic delivery
on the other hand, most water-soluble drugs would revealed high delivery  rate
that would be zero-order for a small percentage of the initial drug load. In the case of low solubility compounds, various other
approaches may be applied and can be divided into two categories. First, swell- able polymers can be added that gives in the delivery of poorly soluble drugs in the form of a suspension. Second,
the drug solubility can be altered by using different techniques. Semi permeable Membrane:
                  
The selection of a rate-controlling membrane is an significant characteristic
in the formulation design of osmotic systems. Drug release from osmotic systems is not influenced  by pH and
agitational force of the gastrointestinal tract to a greater  degree because of the reason that selectively water permeable membrane and
operative isolation of dissolution from the gut environment. The thickness of membrane is kept between 200 and 300 mm
·         Use of encapsulated excipients:
                   A
capsule device layered with uneven
membranes to transport drugswith poor water-solubility .For instance , solubility of a poorly
water-soluble drug such as glipizide was increased by using bicarbonate, it was employed as encapsulated excipients (pH-controlling excipients) in the capsule device. The solubility modifier (meglumine), in the form of mini-tablets, was coated  with a rate controlling membrane to delay its availability inside  the core. Thus, the solubility of glipizide was improved to its delayed release from the device.   ·       
Use of cyclodextrin derivatives:
        These enhances  the drug
solubility and dissolution through addition of complexation or solid dispersion which behave as hydrophilic carriers
for drug with inadequate  molecular aspects for complexation, or as tablet dissolution enhancer for drug with high dose, with mixture of a drug/cyclodextrin Complex is
problematic, eg, paracetamol. The same phenomenon can also be
employed  for the osmotic systems 
·         Use of Swell-able polymers:
Polyethylene oxide, vinyl acetatecopolymer have even swelling rate which causes drug release at constant rate.
Also, the pressure build up while swelling does
not rupture the system 
·         Use of wicking agents: These
agents may improve the surface area of drug along with  aqueous fluids. E.g.Sodium lauryl sulfate and colloidal silicon dioxide, etc. Ensotrol® technology works on the same principle for drug
administration via osmotic system.
·         Use of effervescent mixture: It can be new tactic to deliver poorly water-soluble drugs
from osmotic delivery systems. After administration, the effervescent mixture having drug is deliveredunder pressure via 
delivery hole in the membrane 
Effervescent mixture of citric acid and sodium bicarbonate produces carbon
di-oxide which build up pressure in the osmotic system and finally  release the  drug at steady rate 
·         Co-compression of drug with excipients:  Different excipients can be
used to alter the solubility of drugs with mechanisms like
saturation solubility, pH dependent
solubility. For instance, such excipients are organic acids, buffering agent, etc. ·         Use
of alternative salt form: Change in salt form of drug may improve  solubility. It is observed that the salt of drug is too soluble to maintain a saturated solution and thus zero order release for the estimated delivery life of
dosage form. Afterwards osmotic pump is designed with this salt form that give extended
release up to 24 h.
·         Resin Modulation approach:
Ion-exchange resin methods are frequently used to alter the solubility of
drugs.Some of the resins used in osmotic systems are Poly (4-vinyl pyridine), Pentaerythritol, citric and adipic acids.

 

Classification of Osmotic
DDS Osmotic Drug Delivery Devices fall in two categories:  
·         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 initially  designed by the Australian scientists Rose and Nelson, in 1955 when they were
administering drug to  the
sheep and cattle gut Components            This drug delivery system  contains 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 compartment  as the
water enters from water to salt chamber due to gradient build up 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 diseased  area.
B. Higuchi Leeper osmotic pump
              This DDS is the advancement of Rose and Nelson pump, in its design in a way that
it has no water chamber.
Components 1       Salt
chamber 2      
Drug chamber3       Semi permeable membrane 4       A rigid housing Working     As is has no water chamber so through the  of imbibition
method  drug enters the system and activates it .On implantation
of device the biological liquid present
in the environment  enters the salt chamber which comprises of  the fluid solution , on enteringbiological 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 one more time  after drug release
pressure reduces 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 device is a further advancement
of Rose and Nelson pump in 1970
.This system is changed  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 endure highpressure. Drug is loaded prior to  the application in this way this device is used for longer period of time giving the delayed  release. Drug
delivery is governed by the salt in the salt chamber and permeability aspects  of the cell membrane. D. Implantable mini-osmotic pumps      Osmotic pump working on this principle
 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 delayed  drug
is required. For the loss of drug by diffusion delivery port is made  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 absorbs into the system and drug dissolution occurs and the drug solution is diffused 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 insitu. When the system encounters with GIT fluid the polymeric osmotic layer swells up and release 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 agentsolution is made 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 anosmotic
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 layering  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 delivered  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 aids in pulsatile release Modification This system
has resemblance to an elementary osmotic pump instead it lacks delivery orifice and size is smaller. On  placing  in an
gastric fluids, water is absorbs and hydraulic pressure is
developed within membrane  so
that the semipermeable membrane rupture
and the drug is released to the environment. By altering the thickness as well
as the area of semipermeable membrane can be regulated and in turn release of drug.      Liquid Oral
Osmotic system:  It 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 aid 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 comprises of  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 swelling  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 chamber  containing the swelling agents’ swells and the drug is delivered from the two orifices located on alternating 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 contains three 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 connect  the delivery device, the active agent is inserted into one of the sections by manual or
mechanical fill process. The bilayer tablet
with the osmotic engine is inserted  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 loaded 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 apply pressure on the movable connected first and second wall sections. During the delay period the volume of reservoir having  active
agent is kept continuous and steady,
therefore a slight pressure gradient exists between the outer surrounding  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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