POWDERS AS A DOSAGE FORM

OBJECTIVES:

Upon completion of this exercise, the student should be able to:

• List and describe the different types of powders and granules.
• Describe the appropriate uses of pharmaceutical powders and granules.
• Accurately calculate, compound and dispense divided powders and bulk powders found in the handout.
• Apply the information provided in the compounding information section in the filling of prescriptions.

ASSIGNED READINGS

O'Connor, R.E., Schwartz, J.B. Powders, Chapter 37, pp.681-699, in Remington's, 20th ed., Ansel, H.C., Allen, L. V., Popovich, N.G., Powders and Granules, Chapter 6, pp. 186-203, Pharmaceutical Dosage Forms and Drug Delivery,  Systems, 8th ed., USP Pharmacist's Pharmacopeia, pp. 794-796, 1st ed.

BACKGROUND

A powder is a mixture of finely divided drugs and/or chemicals in dry form, and is derived from the Latin word pulvis. A powder may be composed entirely of solid components, or may contain a liquid which has been dispersed evenly throughout the solid components. Powders may be taken internally or applied externally. Powders which are intended for human ingestion may be dispensed in bulk form if potent or toxic drugs are not contained therein. If dose or toxicity is a concern, the pharmacist may be required to dispense the powder in divided form as powder papers or charts.  Granules are a type of powder dosage form, and consist of a mixture of powders that are wetted, dried, and passed through a screen or granulator.  Effervescent granules are an excellent  way to mask bitter or salty tasting medications.

Advantages of powders as a dosage form include flexibility in compounding and relatively good chemical stability. They can be administered to infants easily to infants and young children or adults who cannot swallow tablets or capsules. The onset of action will be rapid since disintegration is not a limiting factor. The disadvantages include the time of preparation required of the pharmacist, and the compounding problems associated with some substances which may be hygroscopic, deliquescent, or bad tasting. If accurate dosing is needed, patients cannot always be relied upon to measure an accurate dose if the powder is to be taken orally.  The product may be messy and bulky.  The patient may find it inconvenient to dose away from home.

There are two methods by which the compounding pharmacist mixes powders for prescriptions compounded on a smaller scale, such as a retail or hospital pharmacy. Spatulation involves movement of a pharmaceutical spatula through the powders on a sheet of parchment paper or on a pill tile. This method is usually reserved for prescriptions on non-toxic substances, since homogeneous mixing is not as certain as with other methods. Very little compression is involved, so this method is appropriate when mixing substances which form a eutectic. The most common and most desirable method of mixing potent drug substances is trituration in a mortar and pestle. If communition is desired, the rough interior of the Wedgewood or porcelain mortar is best. If the substances being triturated will stain a porcelain surface, the glass mortar and pestle are used. Geometric dilution is used in the mixing of all powders.  Uniform particle size is desired to ensure that the particles of the powder mixture settle uniformly.  Course, dense, or large particles will settle quicker than smaller, lighter particles, so it is desirable to attain a uniform mixture prior to dispensing.

The techniques and topics used in the preparation of powders have been covered elsewhere in the pharmaceutics laboratory curriculum. These include particle size reduction, eutectic formation, density of powders, and the preparation of uniform mixtures. These topics should be reviewed. 

Bulk powders may be dispensed in boxes manufactured for this purpose. Divided powders are dispensed in smaller boxes, and the powders weighed out by the pharmacist in individual doses, and dispensed in packets made from weighing paper (glassine) or special cellophane. The technique used to fold powder papers is illustrated in Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems, p. 174.

It should be noted that both types of dispensing containers do not conform to safety packaging standards, and the pharmacist should devise some method to ensure the safe utilization of this product. While compounded products are excluded from the usual USP storage standards, the pharmacist should be mindful of powder products containing a drug or compound which requires special storage. 

Hints for compounding powders:
(these hints are adapted from The Art, Science, and Technology of Pharmaceutical Compounding by Loyd V. Allen, Jr., Ph.D.)

• Powders of the same particle size may be mixed in a plastic bag.  This will minimize the amount of powder in the environment.  This is especially important for minimizing exposure of the pharmacist to the powder particles.  In addition, dust masks should be worn if it desirable to avoid breathing the particles.
• If powders tend to stick together, magnesium stearate can be added in a 1% concentration to promote lubrication of the powder particles.
• Some powders acquire an electrostatic charge, which can cause them to be pretty difficult to work with.  Sodium lauryl sulfate 1% can be added to minimize this problem.
• As in the preparation of ointments, a coffee grinder may be a useful device for reduction of particle size of powder components in the preparation of these products.