Tablet Sweeteners, Tablet Preservativies and Tablet Wetting Agents

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Tablets Colorants

1.5.6 Miscellaneous Excipients

What will you gain?

1.5.6.1 Wetting Agents

1.5.6.2 Dissolution Retardants

1.5.6.3 Dissolution Enhancers

1.5.6.4 Adsorbents

1.5.6.5 Buffers

1.5.6.6 Antioxidants

1.5.6.7 Chelating Agents

1.5.6.8 Preservatives

1.5.6.9 Colourants

1.5.6.10 Flavours

1.5.6.11 Sweeteners

1.5.6.1 Wetting Agents

Wetting Agents in tablet formulation aid water uptake and thereby enhancing disintegration and assisting in drug dissolution. Incorporation of anionic surfactant like Sodium Lauryl Sulphate (SLS) is known to enhance the dissolution.It has been established that SLS improves permeation of drug through biological membrane since it destroys the path through which drug has to pass and thus minimizing the path length for the drug to travel. Wetting agents are mainly added when hydrophobic drug is to be formulated into tablet. SLS, Sodium diisobutyl sulfosuccinate are used as wetting agent in tablet formulation.

1.5.6.2 Dissolution Retardants

Dissolution Retardants are incorporated into tablet formulation only when controlled release of drug is required. Waxy materials like stearic acid and their esters can be used as dissolution retardants.

1.5.6.3 Dissolution Enhancers

They are the agents that alter the molecular forces between ingredients to enhance the dissolution of solute in the solvent. Fructose, Povidone, Surfactants are used as dissolution enhancer.

1.5.6.4 Adsorbents (4)

Adsorbents are the agents that can retain large quantities of liquids. Therefore liquids like Vitamin E can be incorporated into tablets by addition of adsorbents .Most commonly used adsorbents in pharmaceuticals are anhydrous calcium phosphate, starch, magnesium carbonate, bentonite, kaolin, magnesium silicate, magnesium oxide and silicon dioxide. Generally the liquid to be adsorbed is first mixed with the adsorbent prior to incorporation into the formulation. Silicon dioxide when added can play as both glidant and an adsorbent role in the formula.

1.5.6.5 Buffers

Buffers are added to maintain a required pH since a change in pH may cause significant alteration in stability. Most commonly used buffering agent in tablet formulation includes sodium bicarbonate, calcium carbonate, and sodium citrate.

1.5.6.6 Antioxidants

Antioxidants are added in tablet formulation to protect drug from undergoing oxidation. Antioxidants undergo oxidation in place of drug or they block the oxidation reaction or they act as synergists to other antioxidants. Chelators may also act as antioxidant. Most commonly used antioxidants include ascorbic acid and their esters , alpha-tocopherol , ethylene diamine tetra acetic acid , sodium metabisulfite , sodium bisulfite , Butylated Hydroxy Toluene (BHT) , Butylated Hydroxy Anisole (BHA) , citric acid , and tartaric acid .

1.5.6.7 Chelating Agents

Chelating agents tend to form complexes with trace amount of heavy metal ions inactivating their catalytic activity in the oxidation of medicaments. Ethylenediamine tetracetic acid and its salts, Dihydroxy Ethyl Glycine, Citric Acid and Tartaric Acid are most commonly used chelators.

1.5.6.8 Preservatives

Preservatives may be a part of tablet formulation in order to prevent the growth of microorganisms in tablet formulation. Parabens like methyl, propyl, benzyl, butyl p-hydroxy benzoate are used as preservatives.

1.5.6.9 Colourants(1, 4,16)

Colourants neither contribute to therapeutic activity nor do they improve product bioavailability or stability but are incorporated into tablets for purposes like to facilitate identification of similar looking products with in a product line to avoid mix ups, to facilitate identification of products of similar appearance that exist in the lines of different manufacturers, to overcome colour change on aging, disguising of off-colour drugs, for brand image in the market, to enhance the aesthetic appearance of the product to have better patient acceptance. Most widely used colourants are dyes and lakes which are FD & C and D & C approved. Dyes are generally applied as solution especially in the granulating agent. Lakes are usually employed as dry powders for colouring. In general, direct compression tablets are coloured with lakes because no granulation step is used. Natural colourants can be used and generally they do not require the FDA certification before use in drug products. One of the important advantage in using lakes is reduced risk of interaction between the drug and other ingredients as well as colour development is rapid which reduces processing time .While employing wet granulation , care should be taken to prevent colour migration during drying . In any coloured tablet, the formulation should be checked for resistance to colour changes on exposure to light. Reflectance Spectrophotometry, Tristimulus Colourimetric Measurements and Microreflectance Photometer used to measure the colour uniformity and gloss on a tablet surface.

Table.20. Some Commonly Used Pharmaceutical Colourants (Synthetic)

FD & C COLOUR

COMMON NAME

Red 3

Erythrosine

Red 40

Allura red AC

Yellow 5

Tartrazine

Yellow 6

Sunset Yellow

Blue 1

Brilliant Blue

Blue 2

Indigotine

Green 3

Fast Green

1.5.6.10 Flavours(1,4)

Flavors are commonly used to improve the taste of chewable tablets as well as mouth dissolved tablets. Flavors are incorporated either as solids (spray dried flavors) or oils or aqueous (water soluble) flavors. Solids that is dry flavors are easier to handle and generally more stable than oils. Oil is usually added at the lubrication step because of its sensitivity to moisture and their tendency to volatilize when heated during drying. It may also be adsorbed onto an excipient and added during the lubrication process. The maximum amount of oil that can be added to granulation without affecting tableting characteristics is 0.5 to 0.75 %w/w. aqueous flavors are less used because of its instability on aging.

1.5.6.11 Sweeteners(1,4,45)

Sweeteners are added primarily to chewable tablets.

Table.21. Some Of The Sweeteners Used In Tablet Formulation

NATURAL SWEETENERS

ARTIFICIAL SWEETENERS

Mannitol

Lactose

Sucrose

Dextrose

Saccharin

Cyclamate

Aspartame

Saccharin is 500 times sweeter than sucrose. Its major disadvantages are that it has a bitter aftertaste and is carcinogenic. Even cyclamate is carcinogenic .Aspartame is about 180 times sweeter than sucrose. The primary disadvantage of aspartame is its lack of stability in the presence of moisture. When aspartame is used with hygroscopic components, it will be necessary to determine its stability under conditions in which the product can adsorb atmospheric moisture. Aspartame is available in market under the brand NutrasweetO manufactured and marketed by Nutrasweet Company.

Key Phrases

OOnly FD&C and D&C approved colourants can be incorporated into tablet formulation.

OFlavours and Sweeteners are one of the important ingredients of chewable and mouth dissolving tablet formulation.

About the Author

Dr.Mukesh Gohel's picture
Author: Dr.Mukesh Gohel

Dr. Mukesh Gohel is principal, professor at the LMCP, Ahmedabad served in academics for more than 40 years. He provides training in leading pharmaceutical industries in the areas of Design of Experiments and Quality by Design. His current areas of interest are direct compression and improvement of drug dissolution.

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