Diluents

For ease of handling by the patient, A tablet should weigh at least about 50 mg.

Diluents are fillers used to make up the volume of tablets if the tablet is inadequate to produce the volume. Diluents are used as disintegrants in the dispersible and orally disintegrating tablets.

Diluents are used to make of the desired bulk of the tablet when the dose of the drug is very less. Round tablets for ingestion are usually in a size range of 3/16 to 1/2 inches (0.2 to 0.5 inches). Tablet smaller than about size difficult to handle and larger than is difficult to swallow.

Example:

1. Lactose,
2. Spray-dried lactose,
3. Microcrystalline cellulose (Avicel 101 and 102),
4. Mannitol,
5. Sorbitol,
6. Dibasic calcium phosphate dehydrate,
7. Calcium sulfate dehydrate etc

Lactose is a common bulking agent used in both tablet and capsule formulations as it fulfills most of the ideal characteristics of bulking agents. 

Lactose

Lactose interacts with the amine-containing drug in the presence of metal stearate. Which results in discoloration of the tablet i.e. Millard Reaction. To overcome this problem, Anhydrous lactose is used as diluents.

Spray-dried lactose:

Good Flow Property & good Compressibility

Hydrous lactose:

Used in the wet formulation

Dibasic calcium phosphate dehydrate & Calcium sulphate dehydrate

Never used with tetracycline

Sta-Rx-1500

A free-flowing, directly compressible starch (5-10%)

Hydrolyzed starch

Emdex & Cellutab- they basically mixture of dextrose (90-90%) and maltose (3-5%).

Mannitol

Mannitol having negative heat of solution, solubility and pleasant feeling. It is widely used in chewable tablet.

Mannitol is expensive and it is non-hygroscopic so it can be used in vitamin formulation in which moisture sensivity may be problem

Sorbitol

It is an optical isomer of mannitol. It is relatively hygroscopic but used in combination with mannitol to reduce development cost.

Avicel

It is a microcrystalline cellulose derivative.

Also used as disintegrating agent.