Excipients for granulation can be largely divided into two categories as:
- bulking agents (fillers) and
- functional additives.
Bulking agents generally differ from the functional additives in that they are usually inert materials that are relatively inexpensive.
Functional additives include:
- binders
- disintegrants
- lubricants
- colorants and
- stabilizing agents.
Fillers: Common filler is lactose, although other sugars, dicalcium phosphate, starch, pregelatinized starch, and microcrystalline cellulose are also used.
Disintegrants: The starches and microcrystalline cellulose are also disintegrants in tablets. For tablets, other commonly used disintegrants include
- sodium starch glycolate
- caramellose
- povidone, and
- low-substitutedhydroxypropylcellulose.
Lubricants: Theseare usually not added till prior to filling or tableting of the granules. The most commonly used lubricant is magnesium stearate.
Other lubricants used include:
- calcium stearate
- stearic acid
- wax
- hydrogenated vegetable oil
- talc, and
- starch.
Binders: Binders used in granulation consist of a wide variety of sugars and polymers—natural, semisynthetic, and synthetic.
Sugars used include:
- sucrose
- glucose, and
- sorbitol.
Examples of natural polymers are:
- acacia
- alginic acid
- sodium alginate
- gelatin, and
- starch.
There is an inherent variability in the natural polymers of different batches and this sometimes gives rise to problems in production.
The semisynthetic binders include:
- ethylcellulose
- sodium carboxymethylcellulose
- methylcellulose
- hydroxypropylcellulose, and
- hydroxypropylmethylcellulose.
For each polymer type, a number of viscosity grades are available.
The two types of synthetic binders in use are:
- polyvinylpyrrolidone and
- polyethylene glycol.
Polyvinylpyrrolidone is widely used in both wet massing and fluid bed granulation. The main application of polyethylene glycol as a binder is in melt granulation.
References
- Excipients. Pharmabiro