The general process for preparing powdered formulations includes: crushing, sieving, mixing, dividing doses, quality inspection, and packaging.
1. Crushing and Sieving
The crushing and sieving of medicinal substances are discussed in Unit 3. Based on the properties of the medicinal substances and clinical usage requirements, appropriate crushing methods are employed to obtain fine powder for use.
2. Mixing
Mixing refers to the process or operation of dispersing multiple solid powders uniformly. This operation ensures that the various medicinal components in the powdered formulation are evenly mixed and have a consistent color.
Common mixing methods include grinding and mixing, stirring and mixing, and sieving and mixing. For small-scale preparations, the method of grinding followed by sieving is often used; for large-scale preparations, stirring, sieving, and a combination of stirring followed by sieving are commonly employed. The commonly used mixing methods and operational points for powdered formulations are as follows.
(1) Base Layer and Color Coating Method: This is an empirical method for mixing medicinal powders in traditional Chinese medicine pills and powdered formulations. A small amount of dark-colored powder is first placed in the mortar as a base, known as “base layer”; then, a larger amount of light-colored powder is gradually added in portions to the mortar, lightly grinding and mixing until all powders are uniformly blended, referred to as “color coating”.
(2) Equal Increment Method: Generally, two medicinal substances with similar physical states and powder fineness that are approximately equal in quantity mix easily. However, when there is a significant difference in the proportions of the substances, uniform mixing becomes difficult. In such cases, the “equal increment method” should be used, where the smaller quantity is first mixed with an equal amount of the larger quantity, then an equal amount of the larger quantity is added again and mixed, continuing this process until all of the larger quantity is added and mixed uniformly. This method is time-efficient and effective, making it an important technique in mixing operations. During the grinding and mixing process, attention should be paid to the following issues: ① Generally, a small amount of the larger quantity should be added to the mortar first to saturate the surface energy of the mortar (i.e., filling the gaps on the mortar surface with powder) to avoid loss due to the smaller quantity being directly added and absorbed. ② When the bulk densities of the medicinal substances differ significantly, the “lighter” substance should be placed in the mortar first, followed by an equal amount of the “heavier” substance to mix uniformly, thus preventing the lighter substance from floating and the heavier substance from sinking to the bottom, which would result in uneven mixing of the powders.
3. Dividing Doses
Dividing doses refers to the operation of dividing the uniformly mixed powdered formulation into equal weight portions according to the required dosage. Depending on the properties and quantities of the powdered formulation, the following methods can be selected.
(1) Visual Estimation Method: This involves estimating the total amount of powdered formulation visually and dividing it into equal portions. This method is simple and easy to perform, suitable for small-scale preparations in pharmacies, but has a larger error margin, which can reach 10% to 20%. Toxic or expensive powdered formulations should not use this method.
(2) Weight Method: This method involves weighing each portion according to the specified dosage using a hand scale or balance. This method is accurate but has low efficiency. It is commonly used for powdered formulations containing toxic or expensive materials.
(3) Volume Method: This is currently the most widely used method for dividing doses. The common dosing device for powdered formulations is a measuring spoon made of wood, horn, metal, or plastic. Some spoons have a movable wedge inside to adjust the required dosage. For large-scale production, automatic dosing machines and packaging machines for powdered formulations are used. The volume method is suitable for general powdered formulations, is convenient, efficient, and has a smaller error margin. When using the volume method, attention should be paid to the characteristics of the powder and maintaining consistent scooping conditions to reduce errors.
4. Packaging
Due to the large specific surface area of powdered formulations, they are prone to moisture absorption, caking, discoloration, and decomposition, which can affect efficacy and consumption. Therefore, suitable packaging materials and storage conditions should be selected to delay moisture absorption. Common packaging materials include coated paper, glass paper, wax paper, glass bottles, plastic bottles, hard capsules, aluminum-plastic bags, and polyethylene plastic film bags. Dosed powdered formulations can be packaged in various types of paper into four-corner or five-corner packages, while non-dosed powdered formulations are often packaged in paper boxes or glass bottles. The storage environment for powdered formulations should be cool and dry, and they should be stored separately and checked regularly.
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