Types of Tablet Excipients with Examples

Types of Tablet Excipients with Examples

A tablet contains active ingredients as well as other substances known as excipients, which have specific functions.


Excipients are additive substances used in tablet formulation to improve bulkiness, disintegration, dissolution rate and bioavailability of the drug. Also excipients are inert substances used as diluents or vehicles for a drug.


Criteria for a Good Excipient


All of the excipients must meet certain criteria as follows;

  • Physiologically inert.
  • Acceptable to regulatory agencies.
  • Physiologically and chemically stable.
  • Free from bacteria.
  • Should not interfere with the bioavailability of the drug.
  • Commercially available in the form and purity commensurate to pharmaceutical standards.
  • Low cost or inexpensive.
  • Meet the standards of regulatory requirements.


Excipients Synonyms: Excipients are also known as Additives or Inactive Pharmaceutical ingredients or Nonactive ingredients.


Types of Tablet Excipients

 

There are different types of tablet excipients they are as follows;

  • Diluents/Fillers
  • Binders/Adhesive
  • Disintegrants
  • Anti Frictional agent
    • Lubricants
    • Glidants
    • Antiadherents
  • Organoleptic additives
    • Colors
    • Flavouring agents.
    • Sweetener
  • Coating materials
  • Co-processed Excipients


#01 Diluents/Fillers


Diluents are components that are incorporated into tablets to increase dosage form volume or weight.


Diluents are designed to make up the required bulk of the tablet when the drug dosage itself is inadequate to produce this bulk. Diluents are known as Fillers or Bulking Agents.


Diluents are used as disintegrants in dispersible and orally disintegrating tablets. The most important note is the only diluent is adjusted with the total quantity of active after potency calculation.


Diluents provide better tablet properties such as to provide improved cohesion, improve flow, allow direct compression manufacturing, and adjust tablet thickness or weight.


Some examples of diluents are;

  • Mannitol: It is widely used in chewable tablets. Low calorie content and non-carcinogenic. Mannitol has poor flow characteristics and usually requires fairly high lubricant levels.
  • Dicalcium phosphate: Excellent diluent  for water-sensitive drugs. Tetracycline products made with calcium phosphate diluent had less than half the bioavailability of the standard product. 
  • Divalent cations (Ca++) form insoluble complexes and salts with a number of amphoteric or acidic functionality antibiotics, which generally reduces their absorption.
  • Lactose: Most widely used diluent for tablet formulation. Lactose reacts with amine drug (aminophylline and amphetamine) in presence of alkaline lubricants e.g. metal stearates (e.g. magnesium stearate) and gradually discolours (dark brown) with time due to the formation of furaldehyde. This reaction is called the Maillard reaction.
  • Sorbitol: It is an optical isomer of Mannitol. It is hygroscopic at humidities above 65%.
  • Sucrose: Some sucrose based diluents are;
    • Sugar tab; 90 to 93% sucrose + 7 to 10% invert sugar. 
    • Di Pac; 97% sucrose + 3% modified dextrins. 
    • Nu Tab: 95% sucrose + 4% invert sugar + small amount of corn starch + Mg-stearate. 


Some other diluents are; 

  • Calcium sulfate.
  • Dry starch.
  • Cellulose.
  • Kaolin.
  • Sodium chloride.


#02 Binders/Adhesive


Binders are agents used to impart cohesive qualities to the powdered material are referred to as binders or granulators.


They improve the free-flowing qualities by the formation of granules of desired size and hardness.


Materials commonly used as binders include;

  • Acacia gum
  • Hydroxypropylmethylcellulose
  • Tragacanth
  • Polyvinyl pyrrolidone (PVP)
  • Corn starch
  • Microcrystalline cellulose
  • Gelatin, etc.


#03 Disintegrants


A disintegrant is a substance or a mixture of substances added to a tablet to facilitate its breakup or disintegration into small units/fragments and allow a drug substance to fast dissolution.


When disintegrants come in contact with water or stomach or intestinal fluid, they absorb liquid and start to swell, dissolve, or form gels. This causes the tablet structure to rupture and disintegrate, making increased surfaces for improved dissolution of the drug substance. Disintegrants are vital excipients for tablets.


Examples of major disinfectants are;

  • Microcrystalline Cellulose 
  • Pregelatinized Starch
  • Cornstarch
  • Chitosan
  • Sodium Starch Glycolate
  • Calcium Alginate
  • Calcium Sodium Alginate
  • Magnesium Aluminum Silicate.


#04 Anti Frictional Agent


The agents which reduce friction are known as Antifrictional agents. There are different types of anti frictional agents used in tablets.


Lubricants


They reduce friction between the powder mix and the die walls during compression and ejection.


Lubricants reduce inter-particle friction and thus, improve flow rates of powders or granules.


The best lubricants are those with low shear strength but strong cohesive tendencies perpendicular to the line of shear.


Widely used lubricants in tablets are;

  • Magnesium stearate
  • Sodium Lauryl Sulphate
  • Calcium stearate
  • Talc
  • Stearic acid
  • Hydrogenated vegetable oils
  • Polyethylene glycols (PEG), etc.


Glidants


Glidants are also known as Anticaking agents. These are used to promote powder flow and to reduce the caking or clumping that can occur when powders are stored in bulk.


Most widely used glidants in tablet production are;

  • Colloidal silicon dioxide (Aerosil 200/Cab-o-sil)
  • Talc (asbestos-free)


Some other glidants are;

  • Tribasic Calcium Phosphate
  • Calcium Silicate
  • Cellulose Powder
  • Magnesium Oxide
  • Sodium Stearate
  • MagnesiumSilicate
  • Silica Dental-Type
  • Magnesium Trisilicate
  • Hydrophobic Colloidal Silica, etc.


Antiadherents


These are used for the purpose of reducing the sticking or adhesion of any of the tablet ingredients or powder to the faces of the punches or to the die wall.


Some of the anti adherents are; 

  • Talc
  • Corn starch
  • Cab-O-Sil
  • Syloid
  • DL-leucine
  • Sodium Lauryl sulphate, and
  • Metallic stearates.


#05 Organoleptic Additives


The agents which promote appearance and palatability of pharmaceutical dosage forms are known as organoleptic additives.


If the product does not have acceptable colour, flavor and taste the patient would try to avoid using it.


Colouring Agents/ Colorant


The agents which impart colour to the tablets are known as Colouring agents or Colorant. They help to protect photolabile components of the dosage form.


Coloring agents are categorized into;

  • Dyes: Water-soluble coloring substances,
  • Lakes: Insoluble forms of a dye that result from its irreversible adsorption onto a hydrous metal oxide.
  • Inorganic pigments: Substances such as titanium dioxide or iron oxides, and
  • Natural colorants: Colored compounds not considered dyes, such as riboflavin.


Some of the colorants widely used in tablets are;

  • FD & C Red #40 or Allura Red AC
  • FD & C Blue #1 or Brilliant Blue FCF
  • FD & C Red #3 or Erythrosine
  • D & C Yellow #10
  • Riboflavin (Lactoflavin), etc.


Flavouring Agents


These are the agents which can produce a taste or aroma (i.e. fragrance) response when orally consumed or smelled.


Flavors are vital excipients for chewable tablets, oral disintegrating tablets, dispersible tablets, oral solutions, and oral suspensions to mask the unpleasant smell as well as taste and to make the product more palatable, thus increasing patient compliance.


Some examples of flavouring agents are; 

  • Eucalyptus Oil
  • Peppermint Oil
  • Rose Oil
  • Thymol
  • Menthol / Racementhol
  • Strawberry flavor powder
  • Orange flavor powder
  • Lemon flavor powder
  • Citrus oil
  • Cardamom tincture, etc.


Sweeteners


These are the substances used to mask the unpleasant taste and sweeten oral dosage forms and also to mask unpleasant flavors.


Mainly used in chewable, effervescent & mouth dissolving tablets for improvement of taste.


Examples of sweeteners:

  • Sugar
  • Mannitol
  • Saccharin
  • Cyclamate
  • Aspartame
  • Dextrose, etc.


#06 Coating Materials


The substances which are  used to coat tablets or particles are known as Coating materials. Coating may be enteric or non enteric.


Examples of Coating materials are;

  • Filmformers
  • Solvents
  • Plasticizers
  • Colourants
  • Opaquant-Extenders
  • Miscellaneous coating solution components, etc.


#07 Co-Processed Excipients


These are the mixture of one or more excipients used in combination to improve their characteristics. They reduce the number of excipients in a formulation. They also reduce the overall cost and time for processing.


Some of the co-processed excipients are;

  • Cellulose and Lactose
  • Lactose and Microcrystalline cellulose
  • Lactose and Maize starch
  • Lactose and PVP
  • Microcrystalline cellulose and Sodium CMC.


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