Excipients & Vehicle

In this blog we are discussing about the What is an excipient in a drug, What is excipients and its types and What is called a vehicle. So read the blog till the end for full information.

What is an excipient in a drug?

 Excipient in drug the substance which are of little or no therapeutic value but are added to the formulation in order to maintain the physiochemical stability or to improve patient acceptability are called as excipients. Liquid dosage forms contains excipients like vehicles, buffers, flavours and perfumes, colours etc. 

What is excipients and its types?

a. Vehicles:

Water is most commonly used vehicle in liquids dosage forms because of its physiological compatibility and lack of toxicity. Sometimes all the ingredients are not soluble in water to form the solution. Hence, different approaches such as cosolvency, pH control, solubilization or complexation are used to increase the Aqueous solubility. If the drug is unstable in Aqueous systems then non-aqueous vehicles are used.

b. Buffers:

• It must be compatible with other excipients and should have low toxicity.

• Commonly used buffering agents are monobasic sodium acetate, sodium citrate, potassium phosphate etc.

c. Tonicity modifiers:

Sodium for injection, for application to mucous membranes and large volume solutions for ophthalmic use must be made iso-osmotic with tissue fluid to avoid pain and irritation. The most commonly used tonicity modifiers are dextrose and sodium chloride.

d. Preservatives:

Preservatives are mainly included in liquid preparations for fungistatic action. Most liquid formulations require preservatives to avoid microbial growth.

• The majority of preservatives are bacteriostatic rather than bactericidal.

• Most commonly used preservatives are benzoic acid, sodium benzoate, alcohol, chloroform, glycerin, propyl paraben and methyl paraben.

e. Antioxidants:

Oxidation may manifest as products with an unpleasant odour, taste, appearance, precipitation, discoloration or even loss of activity.

• The Oxidation of an active ingredient in an oral liquid formulation needs to be prevented using antioxidants.

• Antioxidants act as Free radical scavengers and terminators of chain reaction in auto Oxidation.

• Antioxidants suitable for Aqueous preparations include sodium sulfite, sodium bisulfite, ascorbic acid and citric acid.

f. Sweetening agents: 

sugar based sweeteners including sucrose syrup, of invert syrup are most commonly used sweeteners in oral liquid dosage form. Polyhydric alcohols such as sorbitol, mannitol and glycerol also possess sweetening power and can be included in preparations for diabetic use.

g. Flavours and perfumes:

Due to increased contact of solutions with taste buds, taste of the drug is more noticeable in its dissolved state.

• syrups, flavoured syrups, volatile oils such as cinnamon oil, lemon oil, peppermint oil and chloroform are used in the form of aromatic water, emulsion or Spirit.

• Expectorant liquid are usually flavored with anise water or liquorice extract. Paediatric liquids contain mixed fruit juice and chocolate flavours in sweetened base.

h. Colours:

Colour is added to the liquid dosage form to improve attractiveness etc. Amaranth solution BPC (red), compound tartrazine solution BPC (yellow) are commonly used colours for oral liquid dosage forms.

What is called a vehicle? vehicle use in pharmacy. 

The preferred and most commonly used vehicle in solutions for oral administration is purified water USP / I.P. due to its low cost and toxicity.

• Under normal circumstances tap (drinking) water should not be used to the possibility of chemical incompatibilities within the formulation.

What are the 5 types of water?

1. Non-potent

2. Potable (drinkable) water

3. USP purified water

4. USP water for injection (WFI)

5. USP sterile water for injection

6. LUSP sterile water for inhalation

7. USP bacteriostatic water for injection

8. USP sterile water for irritation

Out of these, purified water is used as vehicle for liquid oral formulations and water for injection for sterile liquids. Other types of water are not used in liquid oral formulations.

Purified water: 

• Used as excipients in the manufacturing of pharmaceuticals ( liquid orals and external use formulations )

• Used for equipment cleaning esp. product contact surfaces of nonsterile chemicals.

• Preparation of bulk chemicals.

• Prepared using potable water as feed.

Types of purification: 

Deionisation, Distillation, In exchange, Reverse Osmosis, Filtration.

The main features of purified water USP are as follows: 

• It should meet ionic, organic, chemical and microbial requirements.

• It is prepared by Distillation, ion exchange method or by reverse osmosis.

• The solid residue is less than 1 mg per 100 mo of evaporated sample.

• It must not be used for the preparation of parenteral formulations.

Purified water Quality Requirements: 

1. Conductivity: 3 stage measurement procedure is used.

2. Total Organic Carbon: 500 ppb limit 

3. Microbial Action Limit: 100 cfu / mo maximum - may be lower for specific process and product applications

4. TOC < 500 ppb or oxidizable substance test

In case of parenteral formulations, water for Injection BP / USP / IP must be used.

Water for injection:

• Used as excipient in the manufacturing of injections ( sterile solution ).

• Used for equipment cleaning esp. product contact surfaces of sterile products.

• Preparation of sterile bulk chemicals.

• Prepared using purified water as feed.

• Method of preparation is multicolumn distillation.

• Must Meet ionic, organic chemical, microbial and endotoxins Requirements.

Water for injection Monographic Requirements:

 1. Should meet all Requirements for purified water.

2. Produced by "distillation or purification process proven to be equal to or superior to distillation" 

3. TOC < 500 ppb 

4. Conductivity < 1.1 uS / cm at 20 °C 

5. Passes Bacterial Endotoxin test - not more than 0.25 EU / ml 

6. Microbial Action Limit: 10 cfu / 100 ml maximum - may be lower for specific process and product applications.

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