Excipients
Excipients are additive substances (inert substances) used in tablet formulation to improve bulkiness, disintegration, dissolution rate and bioavailability of the drug.
In the pharmaceutical industry it include all term which includes various sub-groups comprising diluents or fillers, binders or adhesives, disintegrants, lubricants, glidant, flavors, colors and sweeteners. . All of these must meet following criteria:
a) Physiologically inert.
b) Acceptable to regulatory agencies.
c) Physiologically and chemically stable.
d) Free from bacteria.
e) Should not interfere with the bioavailability of the drug.
f) Commercially available in the form and purity commensurate to pharmaceutical standards.
g) Low cost, inexpensive.
h) Meet the standards of regulatory requirements.
Diluents
Diluents are fillers used to make up the volume of tablet if tablet is inadequate to produce the volume. Diluents used as disintegrants in dispersible and orally disintegrating tablet.
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 then about size difficult to handle and larger than is difficult to swallow.
Example: Lactose, Spray-dried lactose, Microcrystalline cellulose (Avicel 101 and 102), Pvpk30 (Pearlitol SD200 and 25C), Sorbitol, Dibasic calcium phosphate dehydrate, Calcium sulphate 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 hydroscopic but used in combination with mannitol to reduce development cost.
Avicel
It is a microcrystalline cellulose derivative.
Also used as disintegrating agent.