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Excipients: Types, Examples, Uses and Functions,

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Introduction

In drugs formulation, there are other ingredients or substances that are added or used in the process other than the active pharmaceutical ingredients. These substances are called inactive Pharmaceutical ingredients or excipients. Excipients are inert substances used as diluents or vehicles for a drug. They are used for various reasons and their functionalities often determine where they are classified. Some excipients serve different functions in drugs formulation.

Criteria excipients must meet

Ideal excipients should:
  1.  Be physiologically inert.
  2. Be acceptable to regulatory agencies.
  3. Be physiologically and chemically stable.
  4. Be free from bacteria.
  5. Not interfere with the bioavailability of the drug.
  6. Be commercially available in the form and purity commensurate to pharmaceutical standards.
  7. Be inexpensive.
  8. Meet the standards of regulatory requirements

Types of excipients

Excipients are grouped or classified based on their role or function in drug formulation. Because of this, it should not be out of place to see a particular excipient, say Starch, under different classes. The following are the types and examples of excipients used in drugs formulation.
  1. Antioxidants
  2. Binders
    • Dry binders
    • Wet or Solution binders
  3. Coating Agents
  4. Colours and Pigments
    • Dyes
    • Lakes
  5. Bulking Agents / Dilutents / Fillers
  6. Disintegrants
  7. Emollients
  8. Emulsifying agents
  9. Flavouring agents
  10. Glidants
  11. Antiadherents
  12. Humectants
  13. Lubricants
  14. Plasticisers
  15. Preservatives
  16. Propellants
  17. Protective colloids
  18. Sialagogues
  19. Surfactants
  20. Suspending agents
  21. Sweetners
  22. Taste masking agents
  23. Viscosifiers

1. Antioxidants

Antioxidants are excipient used to protect active pharmaceutical ingredients that degrade in the presence of oxygen and peroxides.

Examples of Antioxidants

  1. Butylated hydroxyanisole
  2. Butylated hydroxytoluene
  3. Sodium metabisulfite
  4. Citric acid

2. Binders

From the name, these excipients hold the active ingredient in a tablet dosage form together to allow for formulation. They are either used dry or wet depending on the granulation process in use. That’s to say that binders are subclassified into
  • Solution or wet binders
  • Dry binders

Examples of Binders

  1. Dextrin
  2. Dextrose
  3. Maltodextrin
  4. Zein
  5. Starch
  6. Alginic acid
  7. Sodium alginate
  8. Carboxymethyl cellulose sodium
  9. Microcrystalline cellulose
  10. Hydoxylpropyl cellulose
  11. Powered cellulose
  12. Tragacanth
  13. Povidone
  14. Methylcellulose
  15. Guar gum
  16. Confectioner’s sugar

3. Coating Agents

These agents are what is used in drugs coating. The essence of drugs coating has been discussed in detail under Tablet Coating which includes to mask mask bitter taste or odour, to confer stability, to enhance looks and acceptability, to control active ingredient release profile etc.

Examples of Coating Agents

  1. Carboxymethyl cellulose
  2. Cellulose acetate phthalate
  3. Ethyl cellulose
  4. Hydroxyl Propyl cellulose
  5. Methylcellulose
  6. Gelatin
  7. Carnauba wax
  8. Hypromellose
  9. Maltodextrin
  10. Starch
  11. Sucrose
  12. Zein

4. Colours and pigments

These are excipients used to improve aesthetic look in final products. In liquid dosage form, dyes are used. Dyes are a type of colouring agent for Pharmaceutical Products. Another type are lakes used in chewable tablets and coating solution for tablet. Colouring agents can be natural or synthetic.

Examples Colouring Agents

  1. Titanium dioxide: White
  2. Amaranth: Red
  3. Brilliant blue: Blue
  4. Saffron: Yellow
  5. Caramel: Brown
  6. Carmine: Indigo

5. Bulking agents / Dilutents / Fillers

These excipients are used to bulk up low dose active ingredients to facilitate their formulation into a desired dosage form. When added, they allow for easy compression of tablets or encapsulation.

Examples of Bulking agents

  1. Dextrin
  2. Dextrose
  3. Maltodextrin
  4. Dextrates
  5. Starch
  6. Sucrose
  7. Lactose
  8. Mannitol
  9. Calcium carbonate
  10. Calcium sulfate
  11. Powered cellulose
  12. Microcrystalline cellulose

6. Disintegrants

These are substances that are added to oral solid dosage forms to facilitate their breakdown in gastrointestinal tract. When capsules and tablets breakdown into large particles, then to small particles from their original size or form, their surface area is increased and this increases their dissolution rate.

Examples of disintegrants

  1. Alginic acid
  2. Sodium alginate
  3. Sodium starch glycolate
  4. Guar gum
  5. Polyacrilin potassium
  6. Crospovidone
  7. Croscarmellose sodium
  8. Microcrystalline cellulose

7. Emollients

In the formulation of topical preparations such as creams, Lotions and ointments, these materials are used to provide smoothness and softness to the skin. They are equally used to adjust the consistency of the products. Emollients are usually used together with emulsifying agents for better results.

Examples of Emollients

  1. Glyceryl monostearate
  2. Glycerin
  3. Polyethylene glycol
  4. Petrolatum
  5. Isopropyl myristate

8. Emulsifying Agents

Emulsifying agents is also known as emulsifiers. In the formulation of emulsions, micelle formation is important. An emulsion is a biphasic preparation where two or more immiscible liquids are forced to mix and remain together by decreasing the kinetic energy between them using emulsifying agents. These excipients lower surface tension between these immiscible liquids or between liquid and solid. They are used to stabilise emulsions by preventing or reducing the coalesce of dispersed globules by lowering the interfacial tension and form film at the interface of the emulsion. These agents are surface active as they adsorb to the newly formed oil-water interface during emulsion preparation. This ensures that the formed emulsion do not recoalesce or cream.

Examples of Emulsifying Agents or Emulsifiers

  1. Carbomer
  2. Carrageenan
  3. Lanolin
  4. Lecithin
  5. Mineral oil
  6. Oleic acid
  7. Oleyl alcohol
  8. Pectin
  9. Poloxamer
  10. Polyethylene sorbitan
  11. Fatty acid esters
  12. Triethanolamine

9. Flavouring Agents

Flavours or flavouring agents are used in the pharmaceutical formulations to improve the quality of taste of the final products. This increases the acceptance of drugs by patients especially the pediatrics.

Examples of Flavouring Agents

  1. Clove oil
  2. Citric acid syrup
  3. Rose oil
  4. Orange oil
  5. Menthol
  6. Almond oil
  7. Benzaldehyde
  8. Ethyl acetate
  9. Vanillin
  10. Ethyl vanillin
  11. Peppermint oil
  12. Peppermint spirit

10. Glidants

Glidants are excipients used to improve the flow of powder and granules prior to compaction, compression or encapsulation. They achieve this improvement in flow of powder and granules by inter-particle friction reduction and cohesion.

Examples of Glidants

  1. Talc
  2. Starch
  3. Colloidal silica
  4. Silicates
  5. Magnesium carbonate

11. Anti adherents

These are excipients used to prevent tablets from sticking inside or on the wall of die and from being picked by punches during compression. They are also called anti-sticking agents as a result.

Examples of Anti-adherents

  1. Starch (Cornstarch)
  2. Talc
  3. DL-Leucine
  4. Sodium lauryl sulfate
  5. Magnesium stearate (Stearates)
  6. Colloidal silicate

12. Humectants

Humectants are substances that’s attract and retain water vapour or moisture from the atmosphere. In Pharmaceutical industry, they are used in formulating products such as creams and gels as they prevent them from drying out and their package from cap locking.

Humectants are classified into

  1. Inorganic
  2. Metal organic
  3. Organic
Inorganic and metal organic are however rarely used in formulation because they often have compatibility issues and are corrosive in nature.

Examples of Humectants

  1. Glycerin
  2. Propylene glycol
  3. Sorbitol
  4. Triethanolamine
  5. Glycerol
  6. Ethylene glycol
  7. Polyethylene glycol (PEG)
  8. Diethylene glycol
  9. Dipropylene glycol
  10. Mannitol
  11. Glucose

13. Lubricants

These are Pharmaceutical excipients used in small amounts in tablets and capsules formulation for the sole purpose of friction reduction between particles, tablet’s surface and the walls of die cavity. Moreover, they facilitate tablets compression or compaction and capsules plugs consolidation.

Examples of Lubricants

  1. Magnesium stearate
  2. Calcium stearate
  3. Stearic acid and its derivatives
  4. Polyethylene glycol
  5. Glyceryl monostearate
  6. Isopropyl myristate
  7. Polyvinyl alcohol
  8. Sodium stearyl fumarate
  9. Talc

14. Plasticisers

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