Pharmaceutical Excipients of Tablets
Definition of Pharmaceutical Excipients
“Any substance other than the active drug or prodrug that is included in the manufacturing process or is contained in a finished pharmaceutical dosage form.”
Excipients are not inactive and have an impact on the manufacture, safety, and efficacy of the drug substance in the dosage form.
Purposes served by excipients of tablets
- Provide bulk to the formulation.
- Facilitate drug absorption or solubility and other pharmacokinetic considerations.
- Aid in the handling of “API” during manufacturing.
- Provide stability and prevent denaturation etc.
- Pharmaceutical additives must:
- Be safe in the amount used in the drug.
- Be Non-allergic. Some people may be allergic to some excipients.
- e.g., Many people are lactose-intolerant.
- Not affect the bioavailability and performance of the drug.
- Be manufactured in accordance with good standards
- Roles of Excipients in Pharmaceuticals:
- Modulating solubility & bioavailability of the drug
- Enhancing the stability of the drug in its dosage forms
- Helping drug to maintain a suitable polymorphic form
- Maintaining pH & osmolarity of liquid products
- Acting as antioxidants, suspending agents, emulsifier, aerosol propellants, base, tablet diluents
- Preventing aggregation or dissociation
- Modulating the immunogenic response of drug
Also Read: Pharmaceutical Aids
Ideal Properties of Excipients of tablets
Classification of Excipients Based on Objective of Addition in Dosage Forms
List of Pharmaceutical Excipients of tablets
Following are the pharmaceutical excipients of tablets
Fillers typically also fill out the size of a tablet or capsule, making it practical to produce and convenient for the consumer to use.
The function of fillers:
Fillers add volume and/or mass to a drug substance, thereby facilitating precise metering and handling thereof in the preparation of dosage forms. Used in tablets and capsules.
Typical features of fillers:
A good filler should typically be inert, compatible with the other components of the formulation, non-hygroscopic, relatively cheap, compatible, and preferably tasteless or pleasant tasting.
Plant cellulose and dibasic calcium phosphate are used popularly as fillers. A range of vegetable fats and oils can be used in soft gelatin capsules. Other examples of fillers include lactose, sucrose, glucose, mannitol, sorbitol, calcium carbonate, and magnesium stearate.
Binders hold the ingredients in a tablet together. Binders ensure that tablets and granules can be formed with required mechanical strength, and give volume to low active dose tablets.
Typical features of binders:
A binder should be compatible with other products of formulation and add sufficient cohesion to the powders.
Classification and examples:
Binders are classified according to their application,
Solution binders are dissolved in a solvent (for example water or alcohol can be used in wet granulation processes). Examples include gelatin, cellulose, cellulose derivatives, polyvinylpyrrolidone, starch, sucrose, and polyethylene glycol.
Dry binders are added to the powder blend, either after a wet granulation step or as part of a direct powder compression (DC) formula. Examples include cellulose, methylcellulose, polyvinylpyrrolidone, and polyethylene glycol.
Disintegrants are substances or mixtures of substances added to the drug formulations, which facilitate dispersion or breakup of tablets and contents of capsules into smaller particles for quick dissolution when it comes in contact with water in the GIT.
Ideal properties of disintegrants:
Good hydration capacity, poor solubility, poor gel formation capacity.
Polyvinylpyrrolidone, Carboxymethyl Cellulose, Sodium Starch Glycolate etc.
The coating is a process by which an essentially dry, outer layer of coating material is applied to the surface of a dosage form, and agents which are used in this coating process is called coating agents.
Three types of coating agents are used pharmaceutically,
Function of coating agents:
Protection, masking, elegance, ease of swallowing, identification, etc.
HPMC, MC, HPC etc..
Sorbents are materials that soak up oil from the water.
Types and examples of sorbents:
Natural sorbents- peat moss, sawdust, feathers, and anything else natural that contains carbon.
Synthetic sorbents- polyethylene and nylon etc..
Functions of sorbents:
Sorbent are used for tablet/capsule moisture-proofing by limited fluid sorbing (taking up of a liquid or a gas either by adsorption or by adsorption) in a dry state.
Antiaderents or anti-sticking agents prevent adhesion of the tablet surface to the die walls and the punches and as a consequence counter the picking or sticking of the tablet.
Water-insoluble lubricants such as magnesium stearate can be used as anti-adherent, as can talc and starch.
Lubricants prevent ingredients from clumping together and from sticking to the tablet punches or capsule filling machine. Lubricants also ensure that tablet formation and ejection can occur with low friction between the solid and die wall.
Hydrophilic- Generally poor lubricants, no glidant or anti-adherent properties.
Hydrophobic-Most widely used lubricants in use today are of the hydrophobic category. Examples include magnesium stearate.
Roles of lubricants:
True Lubricant Role:
To decrease friction at the interface between a tablet’s surface and the die wall during ejection and reduce wear on punches & dies.
Prevent sticking to punch faces or in the case of encapsulation, lubricants. Prevent sticking to machine dosators, tamping pins, etc.
Enhance product flow by reducing interparticulate friction
Examples of lubricants:
Polyethylene glycol, Magnesium stearate, Stearic acid and it’s derivatives.
A substance (as colloidal silica) that enhances the flow of a granular mixture by reducing inter-particle friction and that is used in the pharmaceutical production of tablets and capsules.
Functions of glidants:
Glidants are used to promote powder flow by reducing interparticle friction and cohesion. These are used in combination with lubricants as they have no ability to reduce die wall friction.
Fumed silica, talc, and magnesium carbonate.
Preservatives are substances that are commonly added to various foods and pharmaceutical products in order to prolong their shelf life.
Ideal properties of preservatives:
Exert a wide spectrum of antimicrobial activity at low inclusion levels.
Maintain activity throughout product manufacture, shelf life, and usage.
Not compromise the quality or performance of product, pack or delivery system.
Not adversely affect patient safety or tolerance of the product.
Methyl & Ethyl parabens, Propyl paraben, Benzoic acid and its salts, Sorbic acid and its salts.
An antioxidant is a molecule that inhibits the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent.
Ideal Properties of Antioxidants:
Effective at a low, nontoxic concentration
Stable and effective under normal conditions of use, over a wide pH and temperature range
Soluble at the required concentration
Compatible with a wide variety of drugs and pharmaceutical excipients
Free from objectionable odor, objectionable taste
Colorless in both the original and oxidized form
BHT (Butylated Hydroxy Toluene), BHA (Butylated Hydroxy Anisol), Sodium sulfite, Ascorbic acid etc..
Sweetening agents are employed in liquid formulations designed for oral administration specifically to increase the palatability of the therapeutic agent.
Sucrouse, Saccarine, Aspertame, Sorbitol etc.
Uses of sweetening agents:
The main sweetening agents employed in oral preparations are sucrose, liquid glucose, glycerol, sorbitol, saccharin sodium, and aspartame. Aspartame is an artificial sweetening agent.
The use of artificial sweetening agents in formulations is increasing. The use of sugars in oral formulations for children and patients with diabetes mellitus is to be avoided.
Flavoring agents are added to increase patient acceptance. The four basic taste sensations are salty, sweet, bitter, and sour. It has been proposed that certain flavors should be used to mask these specific taste sensations.
Clove oil, citric and syrup, glycerin, rose oil, orange oil, menthol etc..
Coloring agents are pharmaceutical ingredients that impart the preferred color to the formulation.
There are two types of coloring agents
White: Titanium dioxide
Blue: Brilliant blue, Indigo carmine
Red: Amaranth Carmine
Yellow: Saffron 5. Green 6. Brown: caramel
A solvent is a substance that can dissolve a solute (a chemically different liquid, solid or gas) resulting in a solution. A solvent is usually a liquid but it can also be solid or a gas. A solvent never changes its state forming a solution.
Solvents can be broadly classified into two groups:
Normally solvation of a solvent depends upon its classification. Generally polar solvent dissolves polar compound best and non-polar solvent dissolves non-polar compound best.
Example and uses of solvent:
The first choice for a solvent is water in which a drug is freely soluble.
Water–miscible solvent such as Chlordiazepoxide hydrochloride can be used to improve solubility and stability.
Oils are used as emulsion, intramuscular injections and liquid fill oral preparation.
Aqueous methanol is widely used in HPLC and is the standard solvent in sample extraction.
Other acceptable non-aqueous solvents are glycerol, propylene glycol, ethanol and are used generally for a lipophilic drug.
Co-solvents are defined as water-miscible organic solvents that are used in liquid drug formulations to increase the solubility of poorly water-soluble substances or to enhance the chemical stability of a drug.
Properties of co-solvent:
Co-solvent increases the solubility of a drug.
An ideal co-solvent should possess values of a dielectric constant between 25 and 80.
The most widely used system that will cover this range is a water/ethanol blend.
It should not cause toxicity or irritancy when administrated for oral or parental use
Other co-solvents are sorbitol, glycerol, propylene glycol, and syrup.
Chelating agents are molecules that are capable of forming complexes with the drug involving more than one bond it’s a complex compound that contains one or more rings in its structure.
For example EDTA
Example and uses of chelating agent:
EDTA: Ethylene Diamine Tetra Acetate is used for the estimation of metals ions.
EDTAH4: Ethylene Diamine Tetraacetic Acid is used for softening water.
Calcium Disodium Edetate: it is used in the treatment of heavy metal poisoning mostly caused by lead.
Disodium Edetate: it is used in hypercalcemic states. It is also useful in the treatment of cardiac arrhythmias.
These are materials that, when dissolved in the solvent will enable the solution to resist any change in pH. The choice of a suitable buffer depends on the pH and buffering capacity required.
Features of buffering agent:
It should have low toxicity, it should be buffered at the range of 7.4 as the pH of the body is 7.4, it should be non-irritant.
Examples of buffering agents:
Most of the buffering systems are based on carbonate, citrates, gluconates, lactates, phosphates, tartrates etc.
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