A REVIEW ON OSMOTICALLY REGULATED SYSTEMS

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About Authors:
Fiza Farheen*, Sudhir Bharadwaj
Department of Pharmaceutics, Shri Ram College of Pharmacy banmore,
Morena (M.P.) india
fizafarheen31@gmail.com

Abstract
Osmotic devices are most promising strategy based systems for controlled drug delivery. These are among the most reliable controlled drug delivery systems and could be employed as oral drug delivery systems or implant able devices. Osmotic pumps offer many advantages over other controlled drug delivery systems, i.e. they are easy to formulate and simple in operation, improve patient compliance with reduced dosing frequency and more consistent and prolonged therapeutic effect with uniform blood concentration. Drugs can be delivered in a controlled pattern over a long period of time by the process of osmosis. Osmotic pumps consist of an inner core containing drug and osmogens, coated with a semi permeable membrane. As the core absorbs water, it expands in volume, which pushes the drug solution out through the delivery ports. This article highlights the principle of osmosis, materials used for fabrication of pumps, types of pumps, advantages, disadvantages, and marketed products of this system.

REFERENCE ID: PHARMATUTOR-ART-2166

PharmaTutor (ISSN: 2347 - 7881)

Volume 2, Issue 5

Received On: 17/03/2014; Accepted On: 26/03/2014; Published On: 01/05/2014

How to cite this article: F Farheen, S Bharadwaj; A Review on Osmotically Regulated Systems; PharmaTutor; 2014; 2(5); 51-64

INTRODUCTION
During the past three decades significant advances have been made in the area of novel drug delivery. This was in part due to the evolving discipline of biopharmaceutics, pharmacokinetics and pharmacodynamics. In a typical therapeutic regimen the drug dose and dosing interval are optimized to maintain drug concentration within the therapeutic window, thus ensuring efficacy while minimizing toxic effects. Survey indicated that dosing more than one or twice daily, greatly reduces patient compliance. So in recent year considerable attention has been focused on the development of novel drug delivery system and the main reason for this paradigm shift is relatively low development cost and time required for introducing a novel drug delivery system as compared to a new chemical entity.[1]

A number of design options are available to control or modulate the drug release from a dosage form. Majority of per oral dosage form fall in the category of matrix, reservoir or osmotic system. In matrix system, the drug is embedded in polymer matrix and the release takes place by partitioning of drug into the polymer matrix and the release medium. In contrast, reservoir systems have a drug core surrounded\coated by the rate controlling membrane. Osmotic systems utilize the principle of osmotic pressure for the delivery of drugs. Drug release from these systems is independent of pH and other physiological parameter to a large extent and it is possible to modulate the release characteristic by optimizing the properties of drug and system.[2] The oral osmotic pumps have certainly came a long way and the available products on this technology and number of patent granted in the last few years makes it presence felt in the market.[3] They are also known as gastro intestinal therapeutic system. Alza corporation of the USA was first to develop an oral osmotic pump and today also they are the leaders in this field with a technology named OROS. Osmotic drug delivery has come long way since Australian pharmacologist Rose and Nelson developed an implantable osmotic pump in 1955. Next quantum leap in osmotic dosage form came in 1972 when Theuwes invented elementary osmotic pump. After that many of have been invented which enable controlled delivery of almost all drugs.[4]

The bioavailability of drug from these formulations may vary significantly, depending on factors such as physico-chemical properties of the drug, presence of excipient, various physiological factors such as the presence or absence of food, pH of the GI tract, GI motility,etc.[5] To overcome this limitation of oral route is replied by parenteral route. This route offers the advantage of reduced dose, targeting of site and avoiding GI stability, hepatic by-pass of drug molecule.In the recent years, pharmaceutical research has led to the development of several novel drug delivery systems. The role of drug development is to take a therapeutically effective molecule with sub-optimal physicochemical and/or physiological properties and develop an optimized product that will still be therapeutically effective but with additional benefits such as.[6]
· Greater effectiveness in the treatment of chronic conditions,
· Sustained and consistent blood levels within the therapeutic window,
· Enhanced bioavailability,
· Reduced interpatient variability,
· Customized delivery profiles,
· Decreased dosing frequency,
· Improved patient compliance due to simplified dosing schedule,
· Reduced side effects,

OSMOSIS
Osmosis refers to the process of movement of solvent molecules from lowe concentration to higher concentration across a semi permeable membrane. Osmosis is the phenomenon that makes controlled drug delivery a reality. Osmotic pressure created due to imbibitions of fluid from external environment into the dosage form regulates the delivery of drug from osmotic device. Rate of drug delivery from osmotic pump is directly proportional to the osmotic pressure developed due to imbibitions of fluids by osmogen. Osmotic pressure is a colligative property of a solution in which the magnitude of osmotic pressure of the solution is independent on the number of discrete entities of solute present in the solution.(fig.1) Hence the release rate of drugs from osmotic dispensing devices is dependent on the solubility and molecular weight and activity coefficient of the solute (osmogent).[7,8]

PRINCIPLES OF OSMOSIS
The solvent membrane control delivery of agent from the osmotic system across the semi permeable membrane, which in turn drive the agent out. Water influx of osmotic pump can be describe as,

Where dv = water influx
          dt
A = membrane area
h = membrane thickness
P = mechanical permeability
Δ? = osmotic pressure
ΔP = hydrostatic pressure difference between inside and outside the system
σ = describes the lickages of solute through the membrane.

The general expression for the solute delivery rate, dM / dt obtained by pumping through the orifice of the reservoir is given by,

Where C is concentration of solute if dispersed fluid.[9]

OSMOTICALLY CONTROLLED DRUG DELIVERY SYSTEMS
Osmotic pressure is used as driving force for these systems to release the drug in controlled manner. Osmotic drug delivery technique is the most interesting and widely acceptable among all other technologies used for the same. Intensive research has been carried out on osmotic systems and several patents are also published. Development of osmotic drug delivery systems was pioneered by Alza and it holds major number of the patents analyzed and also markets several products based on osmotic principle. 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.

ADVANTAGE OF OSMOTICALLY CONTROLLED DRUG DELIVERY SYSTEMS
· They typically give a zero order release profile after an initial lag.
· Deliveries may be delayed or pulsed if desired.
· Drug release is independent of gastric pH and hydrodynamic condition.
· They are well characterized and understood.
· The release mechanisms are not dependent on drug.
· A high degree of in-vitro and in-vivo correlation (ivivc) is obtained in osmotic systems.
· The rationale for this approach is that the presence of water in git is relatively constant, at least in terms of the amount required for activation and controlling osmotically base technologies.[10,11]

DISADVANTAGE OF OSMOTICALLY CONTROLLED DRUG DELIVERY 

SYSTEM
* Expensive.
* Chances of toxicity due to dose duping.
* Rapid development of tolerance.
* Hypersensitivity reaction may occur.
* Integrity & consistency are difficult.
* Release of drug depends on

  • Size of hole
  • Thickness of membrane
  • Surface area
  • Composition of membrane[12]

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