A REVIEW ON: FORMULATION AND EVALUATION OF FAST DISSOLVING TABLET

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DESIRED CRITERIA FOR ORODISPERSIBLE DRUG DELIVERY SYSTEM
·         It should not require water to swallow, but it should dissolve or disintegrate in the mouth in matter of seconds.
·         It should be compatible with taste masking.
·         It should be portable without fragility concern.
·         It should have a pleasing mouth feel.
·      It should leave minimal or no residue in the mouth after oral administration.
·        Exhibit low sensitivity to environmental conditions as humidity and temperature.
·        Allow the manufacture of tablet using conventional processing and packaging equipment at low cost.

ADVANTAGES OF ORODISPERSIBLE DOSAGE FORM
·       Ease of administration for patients who are mentally ill, disabled and uncooperative
·        Requires no water intake.
·         Quick disintegration and dissolution of dosage form.
·         Overcomes unacceptable taste of the drugs
·        Can be designed to leave minimal or no residue in the mouth after administration and also to provide a pleasant mouth feel.
·         Allows high drug loading.
·         Faster onset of action
·      Convenient - ideal dosage form when fast relief required, for example, pain relief, migraine, or allergy.
·     Liquid medicaments (suspension and emulsion) are packed in multidose container; therefore achievement of uniformity in the content of each dose may be difficult.

Selection of drug candidates for ODTS:
Different types of charerterisitcs are considered for selection of appropriate drug candidates for development of orodispersible tablet
1.Good solubility in water and saliva.
2.Free from bitter taste.
3.Dose lower than 20mg.
4.Small to lower molecular weight.
5.Partially non ionized to oral cavity at ph (6.8).
6.Ability to permeate oral mucosal tissues.
7. Ability to diffuse and parttion into the epithelail of upper part of  GIT.

Wide range of drugs can be considered as a suitable candidate for such type of dosage forms likeAntiulcer agents such as ranitidine, sulpiride. Antipyretic, analgesic, anti-inflammatory agents such as aspirin, ibuprofen, mefenamic acid, Bronchodilators such as salbutamol sulfate terbutaline sulfate, mabuterol hydrochloride, fenoterol hydrobromide, or methoxyphenamine hydrochloride Oral antibacterial and antifungal agents such as penicillin, ampicillin,. Antitussive, anti-asthmatic agents such as theophylline, aminophylline, Diuretics such as acetazolarmide, spironolactone, triamterene, fluorothiazide, Gout suppressants allopurinol, probenecid etc.

LIMITATION OF FAST DISINTEGRATING TABLET
1.Drugs which are having relatively lager doses are difficult to formulate in form of fast disintegrating tablet example like ciprofloxin.

2.The tablets usually have insufficient mechanical strength.Hence careful handaling is required.

3. The tablets may leave unpleasant taste or grittiness in the mouth if not formulated properly.

4. Patients who councurrently taking medicine like anticholenergics may not be the best candidates for fast disintegrating tablets and the patients suffers from sjogren’s syndrome or dryness of mouth due to decrases saliva production may not be good candidate for such type of formulation.

INGREDIENTS TO BE USED FOR FAST DISINTEGRATING TABLET
Important ingredients that are used in the formulation of fast-disintegrating  tablets should allow quick release of the drug, resulting in faster dissolution.This includes both the active and inactive ingridents Excipients balance the properties of the actives in fast-disintegrating tablets. This demands a thorough understanding of the chemistry of these excipients to prevent interaction with the actives. Determining the cost of these ingredients is another issue that needs to be addressed by formulators. The role of excipients is important in the formulation of fast-melting tablets. These inactive food-grade ingredients, when incorporated in the formulation, impart the desired organoleptic properties and product efficacy. Excipients are general and can be used for a broad range of actives, except some actives that require masking agents.

Binders: The choice of a binder is critical in a fast- dissolving formulation for achieving the desired sensory and melting characteristics, and for the faster release of active ingredients. Binders keep the composition of these fast dissolving tablets together during the compression stage. The right selection of a binder or combination of binders is essential to maintain the integrity and stability of the tablet. The temperature of the excipients should be preferably around 30 to 350C for faster melting properties. Binders can either be liquid, semi solid, solid or mixtures of varying molecular weights such as polyethylene glycol.

Lubricants: Lubrications are used for to reduces the friction during compaction and ejection of tablets in present study magnesium stearte and talc were used as lubricant.

Bulking agent: The material contributes functions of a diluent, filler and cost reducer. Bulking agents improve the textural characteristics that in turn enhance the disintegration in the mouth, besides; adding bulk also reduces the concentration of the active in the composition. The recommended bulking agents for this delivery system should be more sugar-based such as mannitol, polydextrose, lactate and starch hydrolysate for higher aqueous solubility and good sensory perception. Lactate in particular has high aqueous solubility and good sensory perception. Bulking agents are added in the range of 10 percent to about 90 percent by weight of the final composition.

Emulsifying agents: Emulsifying agents are important excipients for formulating fast-melting tablets, they aid in rapid disintegration and drug release without chewing, swallowing or drinking water. In addition, incorporating emulsifying agents is useful in stabilizing the immiscible blends and enhancing bioavailability. A wide range of emulsifiers is recommended for fast-tablet formulation, including alkyl sulfates, propylene glycol esters, lecithin, sucrose esters and others. These agents can be incorporated in the range of 0.05 percent to about 15 percent by weight of the final composition.

Flavours and sweetners: The addition of these ingredients assists in overcoming bitterness and undesirable tastes of some active ingredients. Formulators can choose from a wide range of sweeteners including sugar, dextrose and fructose, as well as non-nutritive sweeteners such as aspartame, sugar alcohols and sucralose. The addition of sweeteners contributes a pleasant taste as well as bulk to the composition.nowadays aspartame is most commonly used as an instense sweet sweetening agent in pharmaceutical prepration. Its appropriate sweetning power is 180-200 times that of sucrose. It does not posses bitter after taste.

Role of superdisintegrants: As day’s passes, demand for faster disintegrating formulation is increased. So, pharmacist needs to formulate disintegrants i.e. Superdisintegrants which are effective at low concentration and have greater disintegrating efficiency and they are more effective intragranularly. But have one drawback that it is hygroscopic therefore not used with moisture sensitive drugs.

And this superdisintegrants act by swelling and due to swelling pressure exerted in the outer direction or radial direction, it causes tablet to burst or the accelerated absorption of water leading to an enormous increase in the volume of granules to promote disintegration.

Figure1.1: Mechanism of superdisintegrants by swelling

Mechanism of action of superdisintegrants: The tablet breaks to primary particles by one or more of the mechanisms listed below

I. By swelling

II. By capillary action

III. Because of heat of wetting

IV. Due to disintegrating particle/particle repulsive forces

V. Due to deformation

VI. Due to release of gases

BY SWELLING:
Tablets with high porosity show poor disintegration due to lack of adequate swelling force. On the other hand, sufficient swelling force is exerted in the tablet with low porosity. It is worthwhile to note that if the packing fraction is very high, fluid is unable to penetrate in the tablet and disintegration is again slows down.

Figure 1.2: Disintegration of Tablet by Wicking and Swelling

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