Osmotic drug Delivery system

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Osmotic drug Delivery system:


Osmotic drug delivery :

Osmotic drug delivery systems are new approach for a controlled release dosage form. These systems utilize osmotic pressure for controlled delivery of active agent(s). These systems can be utilized for systemic as well as targeted delivery of drugs . The main reason for the development of a novel drug delivery system is relatively low development cost and time, ease of administration and greater effectiveness in the treatment of chronic conditions and greater patient convenience due to simplified dosing schedule. Osmotic drug delivery

In addition they are having the additional benefits such as:

Sustained and consistent  blood levels within the therapeutic window Enhanced bioavailability Reduced interpatient variability Customized delivery profiles Decreased dosing frequency Improved patient compliance Reduced side effects In addition they are having the additional benefits such as

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Osmosis Osmosis refers to the process of movement of solvent molecules from lower concentration to higher concentration across a semi permeable membrane .Rate of drug delivery from osmotic pump is directly proportional to the osmotic pressure developed due to imbibitions of fluids by osmogen . principle of osmosis : It is mainly based on an  experiment in which a membrane permeable to water but impermeable to sugar is used to separate a sugar solution from pure water. A flow of water then takes place into the sugar solution that cannot be halted until a pressure π is applied to the sugar solution, this osmotic pressure π of the sugar solution is directly proportional to the solution concentration and the absolute temperature.

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It is expressed as Π = Ø c RT where Ø = Osmotic pressure Π = osmotic coefficient c = molar concentration R = gas constant T = Absolute temperature

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osmotically controlled drug delivery systems Osmotic pressure is used as driving force for these systems to release the drug in controlled manner . These systems can be used for both route of administration i.e. oral and parenterals. Oral osmotic systems are known as gastro-intestinal therapeutic systems (GITS). Parenteral osmotic drug delivery includes implantable pumps.

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Osmotic Drug Delivery Devices They fall in two categories 1. Implantable I. The Rose and Nelson Pump II. Higuchi- Leeper Pump III. Higuchi Theeuwes pump IV. Implantable Mini osmotic pump 2. Oral osmotic Pump Single chamber osmotic pump Elementary osmotic pump Multi chamber osmotic pump Push pull osmotic pump Osmotic pump with non expanding second chamber

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Basic Component Of Osmotic Pumps: 1. Drug 2. Osmotic agent 3. Semi permeable membrane 4.plasticizers Drugs : ·Short biological half-life {2-6h} .Highly potent drug ·Required for prolonged treatment eg : nifedipine , glipizide , virapamil .

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Osmotic agents: Osmogents used for fabrication of osmotic dispensing device are inorganic or organic in nature, a water soluble drug by it self can serve the purpose of an osmogent. Inorganic water-soluble osmogents : magnesium sulphate Sodium chloride Potassium chloride Sodium bicarbonate

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Organic polymer osmogents: Sodium carboxymethyl cellulose Hydroxy propylmethyl cellulose Hydroxy ethylmethyl cellulose Methylcellulose Polyethylene oxide Polyvinyl pyrollidine

Semi Permeable Membrane: :

Semi Permeable Membrane : The semi permeable membrane should be stable both to the outer and inner environment of the device. The membrane must be sufficiently rigid during the operational lifetime of the device. 1. The material must posses sufficient wet strength (-10 5 ) and wet modulus so as to retain its dimensional integrity during the operational lifetime of the device. 2. The membrane exhibit sufficient water permeability so as to retain water flux rate in the desired range.

Plasticizers: :

Different types and amount of plasticizers used in coating membrane also have a significant importance in the formulation of osmotic systems. Some of the plasticizers used are Polyethylene glycols Ethylene glycol monoacetate and diacetate- for low permeability Triethylcitrate Diethyl tartarate or Diacetin- for more permeable films Plasticizers:

Rose-Nelson pump: :

It is an implantable pump, which consisted of three chambers: a drug chamber, a salt chamber contains excess solid salt, and a water chamber. The major disadvantage of this pump was the water chamber, which must be charged before use of the pump. The pumping rate of this push-pull pump is given by the equation. dM/ dt = dV / dt x c Where, dM / dt = mass release dV / dt = volumetric pumping rate c = concentration of drug Rose-Nelson pump :

Higuchi-Leeper pump:

Higuchi- Leeper pump It has a salt chamber containing a fluid solution with excess solid salt. Recent modification in Higuchi-Leeper pump accommodated pulsatile drug delivery, The Higuchi-Leeper pump is modified version of Rose-Nelson pump. It has no water chamber.

Higuchi-Theeuwes pump::

The pump consists of an osmotic core containing the drug, surrounded by a semipermeable membrane with a delivery orifice. When this pump is exposed to water, the core imbibes water osmotically at a controlled rate, determined by the membrane permeability to water and by the osmotic pressure of core formulation. Higuchi- Theeuwes pump:

Oral osmotic tablets:

Single chamber osmotic pumps: Elementary Osmotic Pump Core: API ± osmogents Coat: Semi permeable membrane with delivery orifice Moderately soluble API 60-80% constant release Oral osmotic tablets

Multi-chamber osmotic pumps:

Push pull osmotic pump : Multi-chamber osmotic pumps osmotic Core Tablet: Layer 1:  API ± osmogents Layer 2: Polymeric agents Coat: Semi permeable membrane with delivery orifice.

Implantable osmotic systems:

Alzet osmotic pumps Empty reservoir within the core of the pump is filled with the drug or hormone solution to be delivered and is surrounded by salt chamber with impermeable layer between them. To deliver drugs, hormones, and other test agents continuously at controlled rates from one day to six weeks. Implantable osmotic systems

Factors affecting drug release rate: Solubility: :

APIs for osmotic delivery should have water solubility in the desired range to get optimize drug release. However, by modulating the solubility of these drugs within the core, effective release patterns may be obtained for the drugs. Solubility-modifying approaches Use of swellable polymers Use of effervescent mixtures Use of cyclodextrin derivatives Use of alternative salt form Use of encapsulated excipients Use of crystal habit modifiers Co-compression of drug with excipients Factors affecting drug release rate: Solubility:

Osmotic pressure: :

The next release-controlling factor that must be optimized is the osmotic pressure gradient between inside the compartment and the external environment. The simplest and most predictable way to achieve a constant osmotic pressure is to maintain a saturated solution of osmotic agent in the compartment. Osmotic pressure:

Size of delivery orifice: :

To achieve an optimal zero order delivery profile, the cross sectional area of the orifice must be smaller than a maximum size to minimize drug delivery through the orifice. The typical orifice size in osmotic pumps ranges from 600µ to 1 mm. Size of delivery orifice:

Methods to create delivery orifice in the osmotic tablet coating are: :

pump Mechanical drill Laser drill: This technology is well established for producing sub-millimeter size hole in tablets. Normally, CO 2 laser beam (with output wavelength of 10.6µ) is used for drilling purpose, which offers excellent reliability characteristics at low costs. Indentation that is not covered during the coating process Indentation is made in core tablets by using modified punches having needle on upper punch. This indentation is not covered during coating process which acts as a path for drug release in osmotic system. Use of leachable substances in the semipermeable coating : e.g. controlled porosity osmotic . Methods to create delivery orifice in the osmotic tablet coating are:


The following advantages contributed to the popularity of osmotic drug delivery system. 1. They   typically give a zero order release profile after an initial lag. 2. Deliveries may be delayed or pulsed if desired. 3. Drug release is independent of gastric pH and hydrodynamic condition. 4.They are well characterized and understood. 5. The release mechanisms are not dependent on drug. 6. A high degree of in-vitro and in vivo co relation. Advantages

Disadvantage: :

1. Costly 2. If the coating process is not well controlled there is a risk of film defects, which results in dose dumping. 3.Hole Size is critical . Disadvantage:

Marketed products Elementary osmotic pump :

Marketed products Elementary osmotic pump


Osmotic system technology has been extended to allow rate controlled and constant drug delivery. They made once a day dosing practical for many agents. These systems made 4 and 3 times a day regimens obselete . Conclusion:

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