In formulating Fast Dissolving Tablet/Oral Disintegrated Tablet, additional excipients are likely to include a suitable flow aid and lubricant for tablet manufacture. Because the tablet is intended to dissolve in the mouth, ODTs often include flavors and sweeteners to mask the taste of bitter actives. Finally, color may be added to the formulation to add elegance and to aid in identification of the final dosage form.

In the formulation of FDT the most important additives are as fallows

1. Superdisintegrants

Fast Dissolving Tablet require faster disintegration, that’s why superdisintegrants is needed in formulating FDT/ODT. Superdisintegrant used is the one that effective at low concentration and have greater disintegrating efficiency and they are more effective intragranularly. The problem is, 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.

Mechanism of superdisintegrants by swelling

Selecting the superdisintegrant

Although the superdisintegrant primarily affects the rate of disintegration, when used at high levels it can also affect mouth feel, tablet hardness, and friability. Thus, several factors must be considered when selecting a superdisintegrant.

Disintegration. The disintegrant must quickly wick saliva into the tablet to generate the volume expansion and hydrostatic pressures necessary to provide rapid disintegration in the mouth.
Compactability. When manufacturing an ODT, it is desirable to have tablets with acceptable hardness at a given compression force to produce robust tablets that avoid the need to use specialized packaging while maximizing production speed. Thus, a more compactable disintegrant will produce stronger, less-friable tablets.

Mouth feel. To achieve patient compliance, ODTs must provide a palatable experience to the patient. Large particles can result in a gritty feeling in the mouth. Thus, small particles are preferred. If the tablet forms a gel-like consistency on contact with water, however, it produces a gummy texture that many consumers find objectionable.

Flow. As with all direct-compression tablet formulations, attaining good flow and content uniformity is important to achieving the required dosage per unit. In typical tablet formulations, superdisintegrants are used at 2–5 wt % of the tablet formulation. With ODT formulations, disintegrant levels can be significantly higher. At these higher use levels, the flow properties of the disintegrant are more important because it makes a greater contribution to the flow characteristics of the total blend.

2. Taste-masking agents

Taste masking of drug may be achieved with preventing the exposure of drug to the tongue through processing or adding competing taste-masking agents. Exposure of solubilized drug to the oral cavity can be prevented by encapsulation in polymer systems or complexation. The approaches are as follows:
  • Layering the drug onto inert beads using a binder followed by coating with a taste-masking polymer.
  • Granulating the drug and coating with a taste masking polymer.
  • Spray drying the drug dispersed or dissolved in a polymeric solution to get taste-masked particles.
  • Complexation by the use of inclusion in cyclodextrins.
  • Psychological modulation of bitterness.
  • Coacervation to form microencapsulated drug within a polymer.
  • Formation of pellets by extrusion spheronization
3. Sweeteners

Sucrose and other natural sweeteners, such as sorbitol, can be used in effervescent products, although artificial sweetening agents are customary. However, the application of artificial sweeteners is restricted by health regulations. Saccharin or its sodium and calcium salts are used as sweeteners. Aspartame is also employed as a sweetener in effervescent tablets. Earlier, cyclamates and cyclamic acid were the artificial sweeteners of choice, but their use has now been restricted. Some commonly used sweeteners are:
  • Sorbitol
  • Mannitol
  • Hydrogenated starch hydrolysate
  • Maltitol solution
  • Maltitol
  • Xylitol
  • Erythritol
  • Glycerin
  • Sucrose
  • Fructose
  • Maltose