Capsules are used for enclosing nauseous medicaments for internal use. The following formula yields a mass for flexible capsules, which is suitable for all ordinary purposes:
|Gelatin, in thin sheets||24.00|||||4 ounces|
|Syrup, by weight||7.00|||||1 oz. 73 gr.|
|Glycerin, by weight||18.00|||||3 ounces|
|Mucilage of Gum Acacia, by weight||6.00|||||1 ounce|
|Distilled Water||45.00|||||7 ½ fl. ounces|
Mix the syrup, glycerin, mucilage, and water, and soak the gelatin in the mixture; when the gelatin has become uniformly soft, melt on a water-bath. If a softer capsule be required, the mucilage of gum acacia may be replaced by syrup, glycerin, or water, or by mixtures of these ingredients, according to the degree of hardness required.
Capsule moulds are usually oval in shape, and may be made of tin, brass, or aluminium. The stems of the moulds are about 5 centimetres (2 inches) long, and are fixed to one side of a circular or square, wooden or metal, carrier; to the centre of the other side of the carrier is fixed a stout handle. The sizes of capsules in common use are 2, 3, 6, 9, 12, 18, 35 and 53 decimils (0.2, 0.3, 0.6, 0.9, 1.2, 1.8, 3.5 and 5.3 milliliters) (3, 5, 10, 15, 20, 30, 60 and 90 minims), and it is convenient to have all the moulds on each carrier of the same size. In making the capsules, the mass is brought to a suitable consistence on a water-bath (if too hot the capsules will be too thin, and if too cold they will be unnecessarily thick), and the surface layer, if necessary, is removed or drawn to one side; the moulds are then wiped with a piece of cloth permeated with almond or olive oil, and dipped into the melted mass till they are well under the surface. They are then slowly withdrawn and rotated until the gelatin sets. When cold the capsules are drawn from the moulds with the fingers, and are then trimmed with a knife or scissors so as to leave a short length of neck.
In filling the capsules the method adopted is determined by the nature of the material employed. In the case of a dry powder, the empty capsule is simply stretched over a small glass or metal funnel fixed at a convenient height, and the weighed quantity of powder shot into the capsule, and, if necessary, pressed down with a wooden plunger. In most cases, however, the material to be capsuled is made into a mass of semi-fluid or pasty consistence. The excipient used for this purpose must have no action on the gelatin; if water or glycerin be present the amount must be very small. Almond or olive oil and wool fat are sometimes suitable, but liquid or soft paraffin or a mixture of both is the most satisfactory excipient in the majority of cases. Liquid extracts are generally capsuled so that a 6-decimil (0.6 milliliters) (10-minim) capsule represents 2 mils (30 minims) of the normal extract. The extract is prepared without spirit, concentrated to between a fourth and a third of its volume, and made up to a third with a mixture of liquid and soft paraffins. With this admixture the extract is much more easily worked, and does not readily clog the syringe. Creosote should be first mixed with one and a half times or twice its volume of almond oil before putting into soft capsules, on account of the miscibility of creosote with glycerin. Capsules of compound rhubarb powder are made by mixing the powder, made with heavy magnesia, with liquid paraffin until the mixture becomes stiff, adding a little soft paraffin to prevent separation, and filling the capsules with this mass with the aid of a syringe. Extract of ergot when ordered in capsules should be first evaporated to three-fourths of its volume and then made up to the original volume with soft paraffin. Capsules of Easton's Syrup are made by omitting the free acid and syrup, and mixing the required proportions of the salts with liquid and soft paraffin, so that 6 decimils (0.6 milliliters) (10 minims) of the mixture represents 4 mils (1 fluid drachm) of the syrup. Syrup of ferrous iodide and syrups of hypophosphites and glycerophosphates, are capsuled in a similar manner. A capsule representing ammoniated tincture of quinine may be made by omitting the alcohol and replacing the ammonia with an equivalent of ammonium carbonate, using an excipient of liquid and soft paraffins and making a mixture of which 3 decimils (0.3 milliliters) (5 minims) will represent 4 mils (1 fluid drachm) of the tincture. Certain limpid liquids are conveniently capsuled by means of a syphon of rubber tubing, terminated by a pointed glass nozzle fixed at a convenient height, the flow being controlled by a spring- or screw-clip, but fluids like castor oil and materials of a semi-fluid or pasty consistence are forced through a nozzle of the required calibre. There are various devices for applying the pressure, but the simplest arrangement is an ordinary glass syringe (the nozzle being drawn out in a gas flame, and cut so as to leave a point of suitable bore), clamped at a convenient height, when the capsule to be filled can be held under the nozzle with one hand, while the piston-rod is manipulated with the other. The filled capsules are placed in trays having cup-shaped holes or carrying pill-boxes of suitable sizes, and may be conveniently closed by heating a metal bolt in a small quantity of the capsule mass thinned down by the addition of a little water and applying to the mouth of the capsule; or a dry bolt, heated by a. small bunsen burner attached to the handle, may be used. The bolt may conveniently be the size and shape of a 10 or 12 decimil (1.0 to 1.2 milliliters) (15 or 20 minim) mould, and when applied to the mouth of a capsule carries sufficient heat to fuse the lips and sufficient gelatin mass to close the capsule. On exposure to air the capsules become drier and firmer, but are permanently flexible.
A recent form of capsule is made from two sheets of tough, gelatinous material. They are known as perles, and may be made spherical like pills, flat like tablets, or oval like the ordinary soft capsule. They are made and filled at the same time, but expensive and complicated machinery is required, which places their production beyond the domain of the pharmacist. Another capsule of American origin sometimes used is cylindrical or cup-shaped, and closed by a lid of the same material and shape which fits tightly over the open end of the capsule; it is not very suitable for liquids. Gelatin capsules are sometimes required to pass through the stomach undissolved, and to release their contents in the intestine. For this purpose they may be coated with solution of keratin, or they may be dipped in solution of formaldehyde; when prepared by the latter process they are known as "Glutoid" capsules.
- Capsulae Amylaceae - Cachets