Notes on Development of Formulae of Tablets

Considerations involved in developing formulae of different kinds of tablets are discussed below:

Soluble Tablets:

Soluble tablets have become much popular for administering antibiotics specially for paediatric patients. All the components of a soluble tablet base must be completely soluble, inert, nontoxic and should not contribute any taste of their own.

Lactose and glucose are generally preferred as diluents. A mixture of 4% sodium benzoate and 1% sodium acetate is suitable as lubricant. The materials employed as diluents and lubricants being water-soluble, the moisture level should be carefully controlled. Relative humidity (RH) in the working room should be maintained between 35 and 45%.

Effervescent tablets:

Effervescent tablets are based on a chemical reaction to generate carbon dioxide when a dry mixture is added to water. Thus the formula includes alkali carbonates/bicarbonates and citric/tartaric acids, which evolve carbon dioxide in presence of water. Besides these ingredients the formula may also include sweeteners such as saccharin sodium, flavours such as citrus and berry flavours, and colourants.

A formula for effervescent aspirin tablets is given below:

Lozenge tablets:

Lozenges or troches are intended to be held in the mouth for slow dissolution and release of drug, which provides prolonged (up to 30 minutes) contact for drug with the mouth and throat.

As lozenges are not intended for disintegration but slow dissolution in the oral cavity, no disintegrant is needed in the formula but the proportion of binder should be more.

Drugs administered as lozenges are primarily local anaesthetics, antiseptics, astringents or antitussives. They may also contain antihistaminics, analgesics and decongestants. Such tablets must have a very agreeable taste and flavour. The compression of lozenges is also of higher degree as compared with tablets.

A formula for penicillin lozenges is given below.

Vaginal tablets:

These are ovoid or pear shaped tablets made by compression. They are also known as inserts and are intended for insertion into the vagina where dissolution and release of the medicament take place. They may contain organic iodine such as iodochlor or iodohydroxyquinoline compounds or other antiseptics, astringents or steroids in a soluble base of lactose or sodium bicarbonate.

The tablets are usually buffered to produce the desired pH Such tablets are usually inserted by means of a plastic tube inserter with a plunger. The tablet should be placed in the upper region of the vaginal tract. Vaginal tablets are commonly used in the treatment of Trichomonas vaginitis. Flagyl and Floraquin Vaginal Inserts (Searle) are examples of such tablets.

Chewable tablets:

These tablets have a smooth, rapid disintegration and are designed to be sucked or chewed before swallowing. Mannitol is most commonly used as the tablet base Disintegrants are needed in such tablets.

The sweetener, flavouring agents and lubricant should always be added to the dried granules. Lubricants are usually selected on the basis of their taste Chewable tablets are commonly employed in the preparation of multivitamin, antacid an antibiotic tablets.

A formula for a chewable antacid tablet is given below.

Magnesium trisilicate Dried aluminium hydroxide Mannitol Sodium saccharin Starch paste (5%) Oil of peppermint Magnesium stearate Corn starch

Buccal and sublingual tablets:

These are generally flat and oval in shape intended to bedissolved in the buccal pouch (buccal tablets) or beneath the tongue (sublingual tablets). These tablets contain drugs that are often destroyed, inactivated or not absorbed in the gastrointestinal tract but are absorbed through the oral mucosa. These tablets should not disintegrate but dissolve slowly over a period of 15 to 30 minutes.

However, nitroglycerin and mannitol hexanitrate tablets should dissolve in 2 minutes beneath the tongue for providing fast relief to treat patients of angina pectoris. Steroidal hormones are generally formulated as buccal or sublingual tablets.

A formula for a sublingual tablet is given below.

Hypodermic tablets:

These are not much used in modern practice. Hypodermic tablets were popular amongst physicians who used to prepare extemporaneous injection by dissolving the tablet in ‘sterile water for injection’ and the resulting solution was injected hypodermically. The tablets are prepared either by moulding or compression. The base used should be water-soluble.