How do they make Powder Medicine? – Dispensing Process of Power Medicine

General Compounding Methods:

The dispensing process, irrespective of the powder being in bulk or divided doses, for internal or external use or in a granular form, consists of grinding (if necessary), weighing, mixing (to provide homogeneous admixture) and wrapping.

A. Grinding (Milling)

It is presumed that a student is familiar with the process of grinding and its importance particularly the fact that the size of the particles of a drug influences its physico-chemical properties due to increase in its specific surface affecting rate of absorption.

The milling operation is usually done by the manufacturer of the drug. However, at the compounding stage a pharmacist may have to grind crystalline substances or particles that tend to form lumps. This can be done with the help of mortar and pestle.

This process of size reduction can be performed behind the counter in advance and drugs put on the dispensing shelves duly powdered to save time at the compounding stage. While grinding, excessive pressure need not be applied to the pestle as it leads to sticking of the mortar or to each other. The drug adhering to the pestle or mortar should be scrapped during the operation with the help of spatula. Generally, it is not necessary to sift the powder unless the drug is required to be in smaller size than particular sieve range.

B. Weighing

The pulverized drug is weighed to the required accuracy with the help of a suitable balance as described earlier. A watch glass or a paper with a suitable counterpoise is used for placing the drug while weighing. All ingredients are weighed one after another and kept separately. It may be reemphasized that the drug should be placed either directly from the container on the watch glass or paper or with the help of a spatula.

At no stage the drug is to be touched with hands. Similarly the weights should be removed from the box and replaced using forceps. Due care should be exercised to avoid any contact between the weights and the drugs.

C. Mixing

Mixing is an important operation and the quality of mixing determines the even and uniform distribution of each ingredient in the powders and thereby the accuracy of dosage of each drug. Mixing at the dispensing counter is not done by mechanical devices such as blenders or mixers.

Four alternative methods are available for hand mixing of the medicaments. These methods are trituration, sifting, tumbling or spatulation. The nature of the finished product is to be borne in mind before deciding upon the method. Sometimes it becomes necessary to dissolve an ingredient in a volatile solvent for even distribution e.g., iodine in alcohol using a glass mortar and pestle.

(i) Trituration

Trituration is the most common method using Wedgwood or porcelain mortar and pestle. A mortar which is large enough to hold all the ingredients leaving sufficient space above is selected for the purpose. While handling substances that are likely to react with porcelain, a glass mortar and pestle are to be used.

The ingredients are transferred to the mortar beginning with the one present in smallest quantity and mixed with the pestle with equal proportion of the drug in next higher quantity.

This process of mixing is known as geometric dilution. Geometrical mixing is suitable when potent substances are to be mixed a large amount of diluent. The potent dug is placed upon an approximately equal volume of the diluent in mortar and mixed by trituration. A second portion of diluent equal in volume to the powder mixture in mortar is added, and trituration is repeated, (e.g., 1g potent drug and 15 g diluent should be mixed in such a way :1 +1=2; 2 + 2 = 4; 4 + 4 = 8; 8 + 8 = 16 where 1 is the quantity of potent drug and other quantities represent diluent).

The geometrical dilution is essential to achieve uniform admixture resulting in a homogeneous product. This process of mixing equal quantity of two lots ensures better mixing and is referred to as trituration. If a coloured ingredient is present in the mixture, uniformity in mixing is visually apparent.

Homogeneity in colour of the powder indicates even mixing. Sometimes an edible dye in minute quantity dissolved in a volatile solvent is added to provide a tint to the product to ascertain uniform mixing. Dispensing of potent medicaments warrants dilution with an inert solid by trituration to minimize error in dosage.

(ii) Sifting

Sifting is another method used for mixing. It controls the particle size and brings about homogeneity in distribution of each ingredient.

Particle agglomerates, if any, get broken by this method. The ingredients after simple mixing are sifted through a sieve with the help of a brush or one may use standard sieves for the purpose. Household sieves of fine grade are good enough for this work.

(iii) Tumbling

Tumbling is an extremely simple and expedient method of mixing. However it is useful for sticky particles only. All the drugs are kept in a wide mouth bottle with a tight-fitting cap; taking care that the bottle is large enough to fill up to not more than half of its height with the medicaments.

The bottle is closed and tumbled up and down allowing the particles to fall freely. The process brings about an even randomization of particles of different densities after the bottle is tumbled 8 to 10 times.

(iv) Spatulation

Spatulation or mixing with the help of a spatula is an effective and expedient method when powdered drugs of similar densities are to be mixed. Perfect mixing can be achieved if the particle size range is also similar. The powdered drugs are kept on a tile or a sheet of glazed paper and mixing done with the blade of a spatula.

Most powders are dispensed in divided doses and therefore the mixed ingredients have to be divided in requisite number of doses, each powder representing uniform quantity of each ingredient. This can be achieved by any one of the three methods-

(i) Using powder measures e.g., spoons, boxes, cups etc;

(ii) Making a block of the mixture and cutting it in desired number of parts and;

(iii) Weighing each powder.

The lower edge of the length is brought under the folded edge at the top and creased.

The paper is further folded in a manner that the height of the paper after folding is a little more than the powder box.

The powder paper in this position is put over powder folder of the proper size (in little smaller than the length of the powder box).

The position of the paper ought to be such that folds of equal size are possible on both sides.

After the crease mark is made, it is carefully folded back, one fold under the other, so that the final crease is neat.

The wrapped powders are then arranged in the powder box placing one after the other with the folds up. Sometimes the powders are enclosed in envelopes of a suitable size.

There is another method of enclosing powders. The drug is placed in a small envelope of a suitable size and sealed. Such envelopes are provided with lining of a water impervious material and made of superior paper. This provides an elegant wrapping to the drug. Bulk powders are usually supplied in cylindrical boxes made of cardboard with a metallic rim both for the upper and lower edges.

Granules are an interesting form of dispensing solid medication. When the dose of a medicament is large it is convenient to present it as granules.

Granules are aggregates of particles of the drugs and can be compounded with colours and flavours to make the product attractive and tasteful so that the patient accepts even a large quantity as a single dose. Drugs that are unstable in liquid form can also be dispensed as granules to be mixed with water or another liquid before use.

Sometimes the pharmacist himself may mix granules in a liquid before use if there is the possibility of a drug relating its potency till it is consumed. In such cases the pharmacist states in the directions the period after which the medicament should not be administered.

Sometimes the granules provide effervescence on mixing with water which yields a sparkling liquid giving it a palatable appearance. Ordinary granules do not require special precautions in compounding.

The process includes weighing the ingredients, making due allowance for the loss in granulation; making a cohesive mass with a suitable liquid which evaporates in air or on heating; passing the mass through a suitable sieve; and drying the granules.

Effervescent granules however, require special care and the method is described under special procedures for powders and granules in the following text.