Review on Ion Exchange Resin: An Approach towards Sustained / Controlled Release Delivery System

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About Author: Mr. Mahesh W. Thube*, Dr. Sadhana R.Shahi, Mr. Abhay Padalkar
Mr. Mahesh W. Thube*: Department of Pharmaceutics,
Government College of Pharmacy, Aurangabad - 431 005, Maharashtra, India

Dr. Sadhana R. Shahi: Assisstant Professor, Govt. College of Pharmacy, Aurangabad, Department of Pharmaceutics.

Ion exchange resin (IER) is high molecular weight polyelectrolyte having charged functional site. IER are chemically vinyl, divinyl benzene and polystyrene copolymers. IER in past years have received extensive attention by pharmaceutical industry due to their versatile application. Previously IER were mainly used for water purification only but recently they have been studied for Novel Drug Delivery System. IER are mainly used for taste masking but, they also possess modifying release properties. The IER are complexed with drug to form resinates by batch process or column process. If necessary the resinates are coated with polymeric material by microencapsulation technique. Coated resinates acts as a controllable rate limiting factor for exchange of ions and also for exchange of drug, thus, modifying the release of drugs. The review article highlights the application of sustained and controlled release resinate for the development of various drug delivery system.

Reference ID: PHARMATUTOR-ART-1113

The modern drug delivery system is capable of producing not only sustained release, but also controlled release (i.e., a release rate that is not greatly in?uenced by the gastrointestinal environment) drug delivery system. The oral controlled-release system is usually made of polymers, and the mechanisms of release are generally regulated by diffusion, bioerosion or degradation, swelling or generation of osmotic pressure or exchange of ions. While signi?cant advances have been made in the development of elegant systems to modify the oral delivery of drugs, the basic approaches has remained largely unchanged with the major systems being:
1. Insoluble, slowly eroding, or swelling matrices,
2. Polymer-coated tablets, pellets, or granules,
3. Osmotically driven systems,
4. Systems controlled by ion exchange mechanisms, and
5. Various combinations of these approaches.
Sustained release indicates an initial release of drug sufficient to provide a therapeutic dose soon after administration, and then a gradual release over an extended period. Sustained releases are dosage form that provides medication over an extended time. Controlled release system is able to provide some actual therapeutic control, whether it is of a temporal nature, spatial nature or both. Thus, the system attempts to control drug concentration in the target tissue. This correctly suggests that there are sustained release systems that cannot be considered controlled release.
The important drawback of conventional controlled or sustained release system is dose dumping but the use of IER has solved this problem. The polymeric (physical) and ionic (chemical) properties of IER will release the drug more uniformly than that of simple matrices (because of physical properties only). The better drug-retaining properties and prevention of dose dumping of IER place them as a suitable candidate for sustained or controlled release system.
The review enlightens the emerging application of Ion exchange resin for  sustained/controlled release drug delivery system. It also describes the mechanism of ion exchange process, various systems of resin and marketed available resin with their application.

1.1 Advantages and limitations of a drug formulated into an extended release (ER Dosage form2:
1.1.1 Clinical advantages
1. Reduction in frequency of drug administration
2. Improved patient compliance
3. Reduction in drug level fluctuation in blood
4. Reduction in total drug usage when compared with conventional therapy
5. Reduction in drug accumulation with chronic therapy
6. Reduction in drug toxicity (local/systemic)
7. Stabilization of medical condition (because of more uniform drug levels)
8. Improvement in bioavailability of some drugs because of spatial control
9. Economical to the health care providers and the patient

1.1.2 Commercial/industrial advantages
1. Illustration of innovative/technological leadership
2. Product life-cycle extension
3. Product differentiation
4. Market expansion
5. Patent extension

1.1.3 Potential limitations
1. Delay in onset of drug action
2. Possibility of dose dumping in the case of a poor formulation strategy
3. Increased potential for first pass metabolism
4. Greater dependence on GI residence time of dosage form
5. Possibility of less accurate dose adjustment in some cases
6. Cost per unit dose is higher when compared with conventional doses
7. Not all drugs are suitable for formulating into ER dosage form

1.2 Types of Oral Sustained or Controlled release system3 :
1. Dissolution Controlled Systems
2. Diffusion Controlled systems
    a) Reservoir System
    b) Matrix System
3. Bio erodible Matrix System and Combination of Dissolution and Diffusion Controlled system:
4. Osmotic Systems
5. Ion Exchange Systems

1.2.1 Dissolution Controlled Systems:
As the name indicates the release of drug will be limited by the rate of dissolution.
The two main types are:
a) Encapsulated dissolution Product: The approach is achieved by preparing appropriate salt or derivatives, coating the drug with a slowly dissolving material.
b) Matrix Dissolution Product: Incorporating it into tablet with a slowly dissolving carrier.

1.2.2 Diffusion Controlled systems:
These are characterized by release rate of a drug being dependent on its diffusion through an inert membrane barrier. Two main subclasses are:

a) Reservoir System:
1. The core of drug, the reservoir, surrounding by a polymeric membrane.
2. The nature of membrane determines the rate of release of drug from reservoir.

b) Matrix System:
Homogeneous dispersion of solid drug in polymer mix

1.2.3 Bio erodible Matrix System and Combination of Dissolution and Diffusion Controlled system:
It is the homogeneous dispersion of drug in an erodible matrix and release rate varies with different polymer. It’s difficult to control kinetics owing to multiple processes of release.

1.2.4 Osmotic Systems:
In this system Osmotic pressure provides the driving force to generate the controlled release of drug. The drug is surrounded by semi permeable membrane and release is governed by osmotic pressure.

Fig I: working of Osmotic system

2 IER (Ion Exchange Resin)4:
Ion exchange resins (IER) may be defined as high molecular weight water insoluble polymers containing fixed positively or negatively charged functional groups in their matrix, which have an affinity for oppositely charged counter ions. IER are solid insoluble high molecular weight poly electrolytes that can exchange with surrounding medium reversibly and Stochiometrically.

IER are Styrene (Di Vinyl Benzene) copolymer containing
- Acidic groups: Carboxylic or sulphonic for Cation E.R.
- Basic groups: Quaternary Ammonium for Anion E.R

Based on the nature of the ionic species being interchanged, the IE process is known as either cation exchange (CE) or anion exchange (AE).The IE process is competitive in nature. In practice, drug in an ionic form (usually solution) is mixed with the appropriate IER form a complex, known as ‘resinate’.

The Performance of Resinate Is Governed By Several Factors, Such As5:
1. The pH and temperature of the drug solution;
2. The molecular weight and charge intensity of the drug and IER;
3. Geometry;
4. Mixing speed;

5. Ionic strength of the drug solution;
6. Degree of cross linking and particle size of the IER;
7. The nature of solvent; and
8. Contact time between the drug species and the IER.



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