Fast dissolving tablets (FDT) are solid unit dosage forms which disintegrate or dissolve rapidly in the mouth without chewing and water. FDTs are also called as fast melt, fast disintegrating or orally disintegrating tablets.

Salient Features of Fast Dissolving Drug Delivery System:

 Ease of administration for patients who are mentally ill, disabled and uncooperative.

 Requires no water

 Quick disintegration and dissolution of the 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.

 Ability to provide advantages of liquid medication in the form of solid preparation.

 Cost- effective , hygroscopic , friable.

Methodology Employed For Fdts Formulations:

• Sublimation

• Freeze drying

• Molding

• Spray drying

• Phase transition process

A. The Mechanisms of Granule Aggregation:

 The mechanical strength of a fast dissolving tablet depends on the binding strength of powders and/or granules constituting the tablet.

 The binding mechanisms of agglomeration have been classified into five groups. They are known as solid bridge formation by sintering, liquid bridge formation by surface tension and capillary forces, adhesion and cohesion forces, attraction force between solid particles consisting of molecular, electric and magnetic forces, and interlocking bonds

 When external mechanical forces are applied to a powder mass, the initial reduction in volume is through particle rearrangements. When the rearrangement becomes more difficult as load increases, further compression will result in some type of particle deformation. Two kinds of deformation are possible: elastic and plastic deformation. When subjected to compression, all solids experience more or less elastic deformation, which is reversible when the load is removed.

B.Disintegration Mechanisms :

 Before a tablet dissolves, it has to disintegrate first, unless the tablet is designed for quick surface erosion.

 The materials used as disintegrants include starches, agar, amylose, cellulose and its derivatives, gum and its derivatives, gelatin, resins, and silicone compounds.

 A few mechanisms of action of disintegrants have been proposed. The first mechanism is evolution of gas from an effervescent couple, e.g., sodium bicarbonate with citric acid upon absorption of water. The expansion of gas can be enough to cause the tablet to disintegrate.

 Another mechanism is swelling of disintegrants by absorbing water to break up the tablet structure.

 In the tablet disintegration process, several factors may affect the disintegration. They include the rate of water absorption, porosity of the tablet, processing parameters, and effect of active ingredients, surfactants, binders, and lubricants. Fast disintegration always requires fast absorption of water into the center of the tablet. Thus, having open pore structures inside the tablets is very important for making fast dissolving tablets.

C. Water Absorption :

 Absorption of water into the tablet is important for binding between granules through liquid bridges and for disintegration of the tablet through swelling or dissolution of excipients & through water solid interactions.

 The affinity of a substance to water in its vapor state is generally referred to as hygroscopicity.

Various technologies used in the manufacture of Fast dissolving tablets

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INGREDIENTS:

EXAMPLES:

Advantages of FDTs over conventional dosage forms

Ø FDTs have significant advantages of
both solid and liquid dosage forms. FDTs remain solid till administration and
possess dose accuracy and stability during storage which transform into liquid
form within few seconds after its administration for easy swallowing.

Ø  No chewing needed.

Ø Adaptable and ameanable to existing
processing and packaging machineryCost- effective

Conclusion

The
introduction of fast dissolving dosage forms has solved some of the problems
encountered in administration of drugs to the pediatric and elderly patient, which
constitutes a large proportion of the world's population.

Ø The FDTs have potential advantages
over conventional oral dosage forms with their improved patient compliance;
convenience, bioavailability and rapid onset of action which drawn the
attention of many manufactures over a decade.

Ø FDT formulations obtained by some
of these technologies have sufficient mechanical strength, quick
disintegration/dissolution in the mouth. Many drugs can be incorporated in FDT
especially unpalatable drugs.

Ø The research is still going on.
More products need to be commercialized to use this technology properly. Thus
FDT may be developed for most of the available drugs in near future.