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We have seen the introduction of the osmotic drug deliver and in this blog I will present various types of pumps.

TYPES OF OSMOTIC PUMPS:

1. IMPLANTABLE OSMOTIC PUMPS

A. The Rose and Nelson Pump:

These pumps consists of principally three chambers, one for the drugs, one for salt and one for water. A semipermeable membrane is present between the salt and water chamber. So whenever there is a variation in the osmotic pressure between the salt chamber and water chamber, water starts moving from the water chamber to drug chamber. As a result the volume increases in the salt chamber. A flexible diaphragm is present between the salt chamber and the drug chamber, which eventually leads to the pushing drug out of the orifice.

The rate is given by the equation

dm/dt = dv/dt *c

dm/dt represents the rate of drug release.

dv/dt rate of volume entering the salt chamber.

c represents drug Concentration (1)

B. Higuchi Leeper Pump:

The water chamber is absent in these pumps. And the functioning is by imbibing water form out side the pump. In these pumps, a waxy substance that melts at low temperatures is used for the separation of the drug chamber and osmotic chamber.

The drug is introduced into the pump once it is prepared. These are extensively used in the veterinary purpose. Antibiotics or growth hormones are given to the animal by these pumps through implantation or orally. (1)

C. Higuchi Theuwes pump:

This is less complicated when compared to Higuchi Leeper pump. There is a semi permeable membrane on the external surface. Salt chamber consists of the citric acid and sodium bi carbonate. Whenever the water comes, there will be the release of the CO₂, which leads to the increased pressure on the diaphragm, that eventually leads to the pumping the drug out. (1)

D. Implantable Mini osmotic pump: (2)

These generally consist of drug reservoir, osmotic sleeve and semipermeable membrane (that can manage rate of release) in three layers.

2. ORAL OSMOTIC PUMP

A. Single chamber osmotic pump:

Elementary osmotic pump:

The mechanism is so simple. There is no separate salt chamber. It is made in the form of a tablet, whose outer surface is made up of semi permeable membrane, which consists of small opening. This semi permeable membrane encloses osmogen. Whenever the water enters, squeezing of the membrane occurs, which leads to the pushing the drug out. (1)

B. Multi chamber osmotic pump

1. Push pull osmotic pump:

By this pump, we can deliver the poor water soluble and highly water soluble drugs at equal rate. It seems like bilayer coated tablet. The drug, polymeric osmogen and excipients are present in outer layer. Osmotic, colorings agents, polymers and tablet excipients are present in the lower layer. Both these two layers are compressed as a bilayer tablet and semipermeable membrane is coated on the outer surface. A small pore is formed in the membrane. Whenever the water enters the outer layer, suspension of drug is formed, and expansion of the lower layer occurs which leads to the delivery of the drug. (1)

2.Osmotic pump with non expanding second chamber:

In this case there will be no expansion of second chamber and based on the functioning of this chamber, they are of two types.

In the first type, second chamber helps in dilution of drug solution. This is advantageous because some drugs causes the irritation when they are saturated.

In second type, there are two chambers, one consists of the osmotic agent and the other consists of the drug. Primarily osmotic agent solution is formed which enters the drug solution and then their mixture is released out by means of semiporous membrane present around the chamber. (1)

MISCELLANEOUS

1.Controlled porosity osmotic pump:

It is less complicated osmotic pump. This is generally consists of the drug which forms the core and is surrounded by the semi permeable membrane. This semi permeable membrane consists of the pore through which the drug delivery takes place. In this case the semi permeable membrane is made by phase inversion process. (1)

2.Osmotic bursting osmotic pump:

It is different from EOP is that it do not contain orifice. As the name describes the bursting occurs because of the increase in the osmotic pressure. As the pump enters the aqueous medium, it imbibes water and when sufficient pressure is produced, it leads to busting and the drug will be released. (1)

3.Effervescent activity-based osmotic systems:

Some drugs are poorly soluble at low pH and some they may precipitate. This precipitate may block the orifice. To prevent this hazard, some effervescent substance like potassium bicarbonate is added to the pump. So these compounds will generate carbon dioxide in the acidic environment and prevent the block. (3)

4.Osmotic pump for insoluble drugs:

First of all the osmotic agents surface is treated with semipermeable membrane. Then these are randomized with the drugs that are insoluble. Then again these are compressed which is further coated with the semi permeable membrane. When the pump reaches the aquatic environment, osmotic agents takes the water and increases the hydrodynamic pressure which eventually leads to the release of the drug via pores. (3)

5.Multiparticulate delayed release systems (MPDRS):

This consists of the drug pellets which are coated with the semipermeable membrane. The drug sometimes mixed with osmotic agent and sometimes not. Whenever the aquatic medium comes into contact, they take the water and swell which leads to the formation of the pores. Through these pores the drug will be released. (2)

6. OROS - CT:

This is mainly used for the colon targeting. These usually consist of push compartment which are enclosed in the hard gelatin capsules. The hard gelatin capsules dissolves first and the enteric coating prevents stomach fluids to enter the pump. After reaching intestine the enteric coating will be removed and imbibition occurs. A drug gel is formed in drug compartment which will be released. (2)

7. Liquid Oral Osmotic System (L-OROS):

Drugs are delivered as liquids and solubility problems can be decreased.

By these methods the bioavailability can be increased.

Types:

1.L- OROS hard cap,

2.L- OROS soft cap

3.Delayed liquid bolus delivery system (2)

8. Latest approaches:

A,Sandwiched osmotic tablet (SOT):

B.Telescopic Capsule for Delayed Release

C.Pulsatile delivery based on expandable orifice:

D.Lipid osmotic pump: (2)

References:

1.A review on osmotically regulated devices by
G.Piyush,R.Pankaj,A.Dabeer,A.Ayaj, International journal of pharmacy and life sciences (IJPLS), I(6):302-310

2.Drug delivery through osmotic systems-An overview by T.Ghosh,A.Ghosh, Journal of applied pharmaceutical sciences 01(2):2011:41,42

3. http://www.authorstream.com/Presentation/heet0212-905485-osmotic-pump-heet/ (accessed on 20/11/11)

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