Excipient
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An excipient is an inactive substance used as a vehicle for medication, or an active ingredient. In addition excipients can be used to aid the process by which a product is manufactured. In general, the active substances (such as aspirin) may not be easily administered and absorbed by the human body; they need to be put in some appropriate form. The active substance is then dissolved or mixed with an excipient.
Depending on the route of administration, and medication form, various excipients may be used. For oral administration, see Tablets and Capsules. For rectal administration see suppositories.
Once the active ingredient has been purified, it cannot stay in purified form for very long. In many cases it will denature, fall out of solution, or stick to the sides of the container. To stabilize the active ingredient, excipients will be added to ensure that the active ingredient stays active, and is stable for a long period of time to ensure that the shelf-life of the product makes it competitive with other products. The formulation of these excipients in many cases is considered a trade secret.
Although drugs are chosen primarily for their active ingredients, the other ingredients (excipients) needed to make the tablet, capsule or liquid are just as important. For this reason, excipients are only used when absolutely necessary and in the smallest amounts possible.
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Types of exipients:
Binders
Binders hold the ingredients in a tablet together. Binders are usually starches, sugars, cellulose or modified cellulose such as hydroxypropyl cellulose, lactose, or sugar alcohols like xylitol, sorbitol or maltitol.
Fillers
Fillers fill out the size of a tablet or capsule, making it practical to produce and convenient for the consumer to use. Plant cellulose (pure plant filler) is a popular filler in tablets or hard gelatin capsules. Dibasic calcium phosphate is another popular tablet filler. Soybean or safflower oil is used in soft gelatin capsules.
Disintegrants
Disintegrants expand and dissolve when wet causing the tablet to break apart in the digestive tract, releasing the nutrients for absorption.
Lubricants
Lubricants prevent ingredients from clumping together and from sticking to the tablet punches or capsule filling machine. Common minerals like talc or silica, and fats, e.g. vegetable stearin, magnesium stearate or stearic acid are the most frequently used lubricants in tablets or hard gelatin capsules.
Coatings
Tablet coatings protect tablet ingredients from deterioration by moisture in the air and make large or unpleasant-tasting tablets easier to swallow. For most coated tablets, a cellulose (plant fiber) film coating is used which is free of sugar and potential allergy-causing substances. Occasionally, other coating materials are used such as synthetic polymers, or corn protein zein or other polysaccharides.
Enteric coatings or slow release coatings control the rate of drug release, or determine where the drug will be released in the digestive tract.
Sweeteners
Sweeteners are added to make the ingredients more palatable, especially in chewable tablets or liquids.
Flavors and Colors
Flavors and Colors are added to improve the taste or appearance of a formulation.
Preservatives
Some typical preservatives used in pharmaceutical formulaitons are
- anti-oxidants like vitamin A, vitamin E, vitamin C, and selenium
- the amino acids cysteine and methionine
- citric acid and sodium citrate
- synthetic preservatives like methyl paraben and propyl paraben.