FORMULATION AND EVALUATION OF TASTE MASKED ORODISPERSIBLE TABLETS BY ION – EXCHANGE RESINS
Department of Pharmaceutics,
Chandigarh College of Pharmacy,
Acceptability of any drug dosage form mainly depends upon its taste i.e. mouth feel. In the formulation of oro-dispersible tablet of bitter drug, the main challenge is to mask the bitter taste of drug, because the drug is dispersed and released in mouth. This is more essential in the formulation for pediatric and geriatric, bed ribbon and non-cooperative patients. There are many methods of taste masking but the main objective of this article is to explore method, technology and evaluation to mask taste of bitter drug by ion-exchange resins. Here we will study the formulation and evaluation of various oro-dispersible tablets of bitter drug. This is more economical, easiest and efficient method for taste masking.
Reference Id: PHARMATUTOR-ART-1383
In the case of pediatric & geriatric patients, unpleasant taste should be avoided & leading to noncompliance which result decrease therapeutic efficacy. In the present scenario, this unpleasant & bitter taste of drug clash to the pharmacist. Therefore taste masking of bitter drug is very important. 
ANATOMY & PHYSIOLOGY OF TASTE-
The biological definition of taste (Gustation) - It is a chemical reaction arising from sensory responses of the four main taste perceptions: sweet, bitter, salt & sour.
Taste sensation is arising by the signal transduction from the receptor organs for taste which are commonly known as taste buds. In mammals, taste buds are groups of 35-100 individual elongated “neutroepithelial” cells which are surrounded in exclusive structure in the adjacent epithelium, term as taste papillae. [2, 3]
Effect of age on taste buds-
Cells that make up the taste buds with age wear out , as a result taste buds begin to disappear from roof and the sides of the mouth excepttaste buds that’s are located over tongue. Remaining taste buds becomes less sensitive. Researchers have been proved that Smocking and eating of scalding food may damage to taste buds. This lacking of taste may lead to loss of appetite and poor nutrition.
Taste is a type of medium to experience the world of tastes for infants and young children. It is seen that children are more sensitive to certain taste than any adults, but because taste can be subjective. The mechanism that causes taste sensitivity in youngsters can be difficult to analyze. 
An orally disintegrating tablet (ODT) is defined as a solid dosage form that dissolves or disintegrates quickly in the oral cavity without the need for administration of water. The EP describes ODTs as »uncoated tablets intended to be placed in the mouth where they disperse rapidly before being swallowed« and as tablets which should disintegrate within 3 min. 
FDA defines ODT as »a solid dosage form which contains a medicinal substance or active ingredient which disintegrates rapidly within a matter of seconds when placed upon a tongue« 
ADVANTAGES OF ORO-DISPERSIBLE TABLETS-
* It has benefits like desired hardness, dosage uniformity, extremely easy administration & since no water is required for swallowing these tablets.
* These are suitable for geriatric, pediatric & travelling patients.
* These tablets display a fast & spontaneous de-aggregation in the mouth, soon after it comes in contact during deglutition. 
* The active ingredients in solution are more rapidly absorbed through the pre-gastric route from the mouth, pharynx & esophagus & through gastrointestinal epithelium to produce the desired effect. 
* ODTs are preferred for people suffering from dysphasia, institutional psychiatric patients as well as hospitalized patients suffering from a variety of disorders. [7,8]
* ODTs have also been found to be the dosage form of choice for patients suffering from nausea, vomiting or motion sickness. 
* Formulation of ODT has been studied as one of the ways to improve the bioavailability of poorly water soluble drugs & it has been observed that ODT increase the bioavailability of such drugs. 
It is defined as the apparent reduction of an unpleasant taste by using suitable agent. Taste masking technologies are very important for improving Patient compliance & better therapeutic efficacy. Many oral drug delivery formulations have objectionable taste such as bitterness, saltiness or sourness. For those drugs taste masking is necessary.
METHODS OF TASTE MASKING-
1) Taste masking with flavors, sweeteners & amino acids.
2) Polymer coating of drug.
3) Formation of Inclusion complexes.
4) Ion- exchange resin complex.
5) Solid dispersion.Microencapsulation.
6) Mass extrusion.
7) Multiple emulsions.
8) Development of liposome.
9) Prodrug concept.
10) Spray drying technique.
12) By using lipophilic vehicles like lipids & recithins.
13) Formation of salt or derivatives.
14) Use of amino acids and protein hydrolysates.
15) By viscosity modification. 
There are many methods of taste masking of bitter drug which are written above but here we will study TASTE MASKING BY ION-EXCHAGE RESINS.
TASTE MASKING BY ION-EXCHANGE RESINS-
IERs are solid & suitably insoluble high molecular weight polyelectrolyte that can exchange their mobile ions of equal charge with the surrounding medium.  Synthetic ion exchange resins have been used in pharmacy & medicine for taste masking or controlled release of drug as early as 1950.  Bitter tasting drugs can be absorbed onto ion-exchange resins, thus effectively removing them from solution during the transit through the mouth, at salivary pH 6.7, remains in intact from making the drug unavailable for the taste sensation. Various studies have revealed that ion exchange resins are equally suitable for drug delivery technologies. 
An ion exchange resin is a polymer (normally styrene) with electrically charged sites at which one ion may replace another. Natural soils contain solids with charged sites that exchange ions, and certain minerals called zeolites are quite good exchangers. Ion exchange also takes place in living materials because cell walls, cell membranes and other structures have charges. In natural waters and in wastewaters, there are often undesirable ions and some of them may be worth recovering. For example, cadmium ion is dangerous to health but is usually not present at concentrations that would justify recovery. On the other hand, silver ion in photographic wastes is not a serious hazard, but its value is quite high. In either case, it makes sense to substitute a suitable ion such as sodium for the ion in the wastewater. Synthetic ion exchange resins are usually cast as porous beads with considerable external and pore surface where ions can attach. The resins are prepared as spherical beads 0.5 to 1.0 mm in diameter. These appear solid even under the microscope, but on a molecular scale the structure is quite open (Fig. 2). Whenever there is a great surface area, adsorption plays a role. If a substance is adsorbed to an ion exchange resin, no ion is liberated. Testing for ions in the effluent will distinguish between removal by adsorption and removal by ion exchange. Of course, both mechanisms may be significant in certain cases, and mass balances comparing moles removed with moles of ions liberated will quantify the amounts of adsorption and ion exchange. While there are numerous functional groups that have charge, only a few are commonly used for man-made ion exchange resins. These are:
• -COOH, which is weakly ionized to -COO¯
• -SO3H, which is strongly ionized to -SO3¯
• -NH2, which weakly attracts protons to form NH3+
• -secondary and tertiary amines that also attract protons weakly
• -NR3+, which has a strong, permanent charge (R stands for some organic group)
These groups are sufficient to allow selection of a resin with either weak or strong positive or negative charge. 
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