Ion exchange resin and its application in pharmaceutical dosage forms, and drug delivery systems.

Ion exchange resins are cross linked polymers of polystyrene, up on which a negatively charged or a positively charged functional group can be added to get an anion exchange resin (Resin- )or a cation exchange resin Resin + (Resin + Or Resin- ). When these resins are mixed with drug molecule which has a negative charge in its one or more functional group as a result of polarity, or as in salt form, or as a result of resonance, such a drug can form a complex with a resin as follow.

1.) Resin + Drug-
2. ) Resin- Drug+
*The resulting resin drug complex stability depends on how strong are the acidic or basic functional groups on resin, stronger functional group result in to formation of very stable resin drug complex, and vice a versa , both has its applications in sustained release drug delivery systems, a resin with strong acidic or basic functional group tend to provide a much more delayed drug release, where drug release is bit faster with weak acidic and basic functional group resins.

When Resin- Drug+ or Resin + Drug- complex (drug resinate ) comes in contact with acid(in stomach) or base(in intestine), it start releasing drug molecule in exchange of similar charged ion for example if drug molecule is positively charged, then it is released from Resin- Drug+ complex when it come in contact with Hydrogen Ion( H+) , similarly a Resin + Drug- or basic drug resin complex will start releasing drug when it comes in contact with basic ions ( in intestine ) OH – NH3- .
Release of drug molecule from Resin +Drug complex takes place due to higher concentration of replacing ions (H+ , or OH – NH3- ).

Masking Taste of drug with ion exchange resin:
There are some drugs which are very bitter in taste like Bromhexin and Quinine, patients has very low acceptability for such drugs some time patients vomit and expelling all of the consumed dose which may result in to dosing error, therefore when such drugs are formulated with ion exchange resins which binds such drugs they do not release drug on taste buds over tongue as a result taste of drug is masked, and when it come in contact with gastric acid bromhexin is released in to gut.

Sustained-release drug delivery system:
Ion exchange resins may not alone give capability to formulate it in to a sustained release dosage form , to make it a good sustained release drug delivery system , proper selection of resin is important a resin with strong acidic or basic functional group provides strong complexation with drug therefore are good candidates for delayed drug release, likewise when early release is intended a weaker acidic or basic functional group resins are useful . Drug resinate is also required to be coated with semipermiable film forming polymers, as drug resinate complex can not be solely relied up on for the intended use. ( ethylcellulose ). In order to maintained the sustained release property of ion exchange resin drug complex it is pretreated with polyethylene glycol so that it do not swell and break open the film coating when it come in contact with gastric juice.

Ion exchange resins are required to be washed with, suitable organic solvent, to remove residual organic or chemical impurities in ion exchange resin, followed by washing with purified water, and regeneration if required, before using for actual process. Ion exchange resin are required to comply with requirements listed in 21 CFR 173.25 by US FDA.

Ion exchange resins have many other applications in pharmaceutical dosage form and drug delivery systems like , localized drug release, stabilization of drug molecule for chemical degradation .
Ion exchange resins are widely used in pharmaceutical industry for purification or raw water and in preparation of water for pharmaceutical use.  

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