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:
- Lactose,
- Spray-dried lactose,
- Microcrystalline cellulose (Avicel 101 and 102),
- Mannitol,
- Sorbitol,
- Dibasic calcium phosphate dehydrate,
- 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.
