CHAPTER XXX.

COMPRESSED TABLETS AND TABLET TRITURATES.

Compressed Tablets.

THIS class of remedies, closely allied to lozenges, was introduced about fifty years ago in England, and afterward in this country, under the name "compressed pills." The name, however, is erroneously applied, as pills are understood to be made from a previously prepared plastic pill-mass. Compressed tablets have of late years grown greatly in favor with physicians, but it is questionable whether this form of administering medicines is as universally desirable as some manufacturers would claim; while, in some cases, tablets appear more convenient than pills and powders, it would seem as though the prompt action of certain remedies must be considerably impaired by firm compression. They are lenticular-shaped disks, containing one or more medicinal ingredients, obtained by compressing the substance, in the form of a granular powder, into suitable shape, by means of hand- or steam-power, in specially constructed apparatus.

The composition of all compressed tablets should be such that they will readily undergo disintegration and solution in the stomach, hence they should be made with as little adhesive excipient as possible; like pills, they are intended to be swallowed without previous mastication. When several medicinal agents are to be simultaneously exhibited in tablet-form it is essential, as in the case of lozenges and pill-masses, that they be reduced to very fine powder, in order to insure a uniform composition of the mixture, which is subsequently brought to a granular condition by moistening with a suitable excipient and pressing the damp mass through a sieve of 16 or 20 meshes to the linear inch; the granules, still damp, must be thoroughly dried before they are compressed, otherwise they will adhere to the sides of the moulds. In a few cases, when the substance to be compressed possesses no inherent adhesive properties, dilute syrup is employed as an excipient, or a slight addition of finely-powdered sugar is made, and occasionally, although rarely, finely-powdered acacia is added in the proportion of 3 or 5 per cent. of the total weight of the powdered substance. As a rule, water, various mixtures of alcohol and water, or possibly a mixture of glycerin and water, or of glucose and water, are employed as excipients.

Many substances do not require any excipient at all, and can either be bought in the required granular condition or be easily reduced by grinding in a mortar or mill; to this class belong potassium chlorate,

the alkali iodides, bromides, and chlorides, quinine bisulphate, etc. Fine powders are never adapted for compression, since the air which they carry with them when fed into the mould is confined in the small interstices between the particles, and cannot escape upward or downward; hence imperfect compression results; moreover, fine powders often have a tendency to cake, when they cannot be properly fed into the moulds.

While some substances can be compressed quite readily, others present some difficulty, and, in fact, each substance or combination of substances requires special study and treatment. No rule can be laid down as to the use of excipients, and experience alone will prove the operator's best teacher. Charcoal and substances of a similar noncohesive or spongy character require the addition of about 5 per cent. of powdered acacia, and must be well moistened with a mixture of glucose and water before they can be properly granulated; for such substances it is also preferable to use a No. 12 sieve for granulation. Some authorities recommend the addition of 25 per cent. of sugar in place of acacia; but, although this combination would yield a more soluble tablet, it has been found unsatisfactory in practice. Substances very sparingly soluble in water, such as phenacetin, acetanilid, salol, sulphonal, etc., are improved by the addition of a little starch, and alcohol will serve well to form the mass for granulations.

If tablets, upon solution, are designed to yield effervescent draughts, they may be made by first preparing the corresponding granular effervescent salts (see page 366) and compressing these, or the ingredients upon which the effervescence depends may be granulated separately (preferably in granules of the same size) and then mixed thoroughly just before compression. Thus, if effervescent tablets of lithium citrate or carbonate are wanted, the lithium salt could be granulated with the sodium bicarbonate and a little sugar, while the tartaric acid and the remainder of the sugar should be mixed and separately granulated with alcohol; when both granules are perfectly dry they may be mixed and compressed. All effervescent tablets must be carefully protected against moisture, in air-tight bottles.

Whenever tinctures or fluid extracts are to be administered in compressed tablet form they are preferably evaporated with moderate heat, on a water-bath, to a syrupy consistence, before they are mixed with the other ingredients; if no diluent powder has been prescribed, the syrupy liquid must be incorporated with a mixture of finelypowdered starch and sugar, for the purpose of granulation. Solid extracts may be used either in the form of very fine powder or softened with a little alcohol, diluted alcohol, or water, as the case may be, then incorporated with the vehicle and granulated in the same manner as the syrupy liquids above mentioned.

The preparation of compressed tablets in small quantities may be conveniently accomplished at the dispensing-counter, and various combinations readily furnished on extemporaneous prescriptions. The finely-powdered ingredients, having been intimately mixed and

properly dampened, may be quickly passed through a No. 20 or No. 30 sieve, and the granules rapidly dried by rotating them on a sheet of smooth paper placed in a sieve or on a perforated tray over a stove or other heated surface; as soon as dry the granules should be

FIG. 234.

weighed and divided into the requisite number of parts, which will then be ready for compression.

Different styles of compressors have been designed at various times to suit the purposes of dispensing pharmacists. (See Figs. 234, 235, and 236.) They are all fed on the same principle, and the mode of operating them differs but slightly. The cylinder, base, and piston are usually made of hardened steel, nickel-plated; the base, which is made to project somewhat into the cylinder, as shown in Fig. 234, having been adjusted, the granular substance is carefully fed into the cylinder from a piece of stiff paper, the piston is inserted over the granules, and compression effected either by a sharp blow from a wooden mallet, or by means of a lever, as shown in Figs. 235 and 236. When the tablet has been compressed it can be removed by lifting the cylinder from the base, the tablet adhering to the concave surface of the piston, and gently tapping the piston with the mallet or lever, which expels the tablet. The Smedley compressor (Fig. 235) is provided with a small receptacle, over which the cylinder and piston can be placed and the tablets discharged directly into it.

Simple mould for compressed tablets.

O

FIG. 235.

The Smedley pill-compressor.

The greater the pressure applied, the firmer will be the compression, but, at the same time, the slower will be the disintegration of some compressed tablets; hence only sufficient pressure should be used to cause the particles to cohere properly without crumbling when handled or breaking if allowed to fall.

FIG. 236.

Some substances show a disposition to stick in the mould, and are then removed with difficulty. This tendency can be overcome by the addition of a small quantity of purified talcum and a few drops of liquid petrolatum, which latter may be applied by spraying a solution of it in ether on the granules. By thus lubricating the surfaces of the mould the tablet is readily discharged. In a few cases plain water has been found very serviceable, provided no solvent effect is produced on the substance to be compressed, as, for instance, with phenacetin, salol, naphthalene, etc. If, at any time, a compressed tablet should become fixed in the cylinder or in the concave depression of the piston, or possibly, if fine powder having been inadvertently used, some of it should have been forced between the piston and the sides of the cylinder, and thus fastened have the piston, warm water alone should be used to relieve the trouble; but never should a sharp instrument be employed to loosen the adhering material, as this would be likely to produce rough surfaces or edges, thereby rendering the compressor unfit for use.

Whitall's compressed tablet machine.

For manufacturing compressed tablets on a large scale, special machinery has been constructed to be operated by hand- or steampower. These machines can be so adjusted that a definite quantity of material will be automatically fed into the mould; therefore, as the pressure applied is uniform, the resulting tablets must be of even weight and thickness. Of the various machines made, the Oriole Tablet Compressor (Figs. 237 and 238) possesses some advantages which adapt it also for smaller operations, such as the manufacture of 50 or 100 oneor two-grain tablets, without the loss of material. The improvement consists in a peculiarly-constructed feeder, the shape of which tends to keep the material constantly at the outlet, hence every particle of it will be discharged into the mould; to prevent any change in the character of the mixture to be compressed, an ingenious stirrer within the feeder keeps the material in constant motion toward the outlet.

In the "Oriole," as in all automatic tablet machines, the adjustment of the supply of material must be made tentatively; the die or chamber, in which the granules are compressed, is situated below the plate, its capacity being adjusted by means of a screw which controls the depth to which the lower punch shall be allowed to drop in