3Learning ObjectivesDefine the term extemporaneous compounding, and describe common situations in which compounding is required.Identify and describe the equipment used for the weighing, measuring, and compounding of pharmaceuticals.Use the proper technique for weighing pharmaceutical ingredients.Use the proper technique for measuring liquid volumes.
4Learning Objectives Define the term percentage of error. Explain the common methods used for comminution and blending of pharmaceutical ingredients.Explain the use of the geometric dilution method.Explain the process by which solutions, suspensions, ointments, creams, powders, suppositories, and capsules are prepared.
5NEED FOR EXTEMPORANEOUS COMPOUNDING Compounding might involve mixing a powdered active ingredient with a diluent powder and filling a given number of capsules with the combined materials.
6Compounding Issues Safety Note! Products compounded for veterinary use cannot be used in humans.
7Terms to Remember extemporaneous compounding good manufacturing practice (GMP)
8EQUIPMENT FOR WEIGHING, MEASURING, AND COMPOUNDING Balances: Balance measurements using a counterbalance are made using sets of standardized pharmaceutical weights. An electronic balance is easier to learn and use and is more accurate than other types of balances.Forceps and Spatulas: Forceps should be used when picking up weights so that moisture and oils are not transferred to the weights. Spatulas are used in compounding tasks such as preparing ointments and creams or loosening material from the surfaces of a mortar and pestle.
9EQUIPMENT FOR WEIGHING, MEASURING, AND COMPOUNDING Compounding Slab: This is an ideal surface for mixing compounds because of its nonabsorbent surface.Mortar and Pestle: The coarser the surface of the mortar and pestle, the finer the triturating, or grinding, that can be done.Graduates and Pipettes: Graduates come in two varieties: conical and cylindrical. A pipette is used for measuring liquids with a volume less than 1.5 mL
10EQUIPMENT FOR WEIGHING, MEASURING, AND COMPOUNDING Master Formula Sheet: Prepared by the pharmacist, this sheet indicates the amount of each ingredient needed, lists the procedures to follow, and provides the labeling instructions.
11TECHNIQUE FOR WEIGHING PHARMACEUTICAL INGREDIENTS Weighing of the product is one of the most essential parts of the compounding process. Weighing the exact amount prescribed is essential in compounds for several reasons: the product cannot be “checked” for content once mixed, the quantities weighed out are often very small, and a slight overage could mean a serious overdose for the patient.
14Weighing Pharmaceutical Ingredients 1. Unlock the balance and confirm that it is leveled, front to back and side to side, using the leveling screws at its base. Once this is done, the balance is ready to use. Lock the balance once again, before transferring weight to it.Table 8.1
15Weighing Pharmaceutical Ingredients 2. Place weighing papers on the two pans of the balance. These papers should be of exactly the same size and weight. The edges of the paper on the left-hand pan may be folded upward, to hold the substance to be weighed. Do not place any materials on the weighing pans without using weighing papers.Table 8.1
16Weighing Pharmaceutical Ingredients 3. Unlock the balance to confirm that the balance is still leveled, and then lock it again.Table 8.1
17Weighing Pharmaceutical Ingredients 4. Add the desired weight to the right-hand pan, using forceps to transfer the weight from the weight container.Table 8.1
18Weighing Pharmaceutical Ingredients 5. Place an approximate amount of the material to be weighed onto the left-hand pan, using a spatula to transfer it.Table 8.1
19Weighing Pharmaceutical Ingredients 6. Slowly release the beam using the unlocking device at the front of the balance, and check the balance.Table 8.1
20Weighing Pharmaceutical Ingredients 7. If the amount of the substance being weighed is too great or too small, lock the balance again and use a spatula to add or remove material (Figure 8.2a)Table 8.1
21Weighing Pharmaceutical Ingredients 8. Slowly release the beam using the unlocking device and check for equilibrium.Table 8.1
22Weighing Pharmaceutical Ingredients 9. Once a nearly precise amount of material has been transferred to the pan, a very small adjustment upward can be made by placing a small amount of material on the spatula, holding the spatula over the left pan, and lightly tapping the spatula with the forefinger to knock a bit of the substance onto the pan. This is done with the balance unlocked and the balance beam free to move.Table 8.1
23Weighing Pharmaceutical Ingredients 10. Lock the balance, close the lid, and then unlock the balance to make a final measurement. (At this point, have the pharmacist check the measurement.) (Figure 8.2b)Table 8.1
24Weighing Pharmaceutical Ingredients 11. Lock the balance before removing the measured substance. Use transfer forceps to remove the weights and return them to their storage case.Table 8.1
25Terms to Remember Class III prescription balance counterbalance spatulasforcepscompounding slabmortar and pestlepipettegraduatesmaster formula sheet
26TECHNIQUE FOR MEASURING LIQUID VOLUMES A general rule of thumb is to always select the device that will give you the most accurate volume. Selecting a container that will be at least half full when measuring, or using the smallest device that will hold the required volume, is considered good practice.
28Measuring Liquid Volumes 1. Choose a graduate with a capacity that equals or very slightly exceeds the total volume of the liquid to be measured. Doing so reduces the percentage of error in the measurement. In no case should the volume to be measured be less than 20% of the total capacity of the graduate. For example, 10 mL of liquid should not be measured in a graduate exceeding 50 mL in capacity. Again, the closer the total capacity of the graduate to the volume to be measured, the more accurate the measurement will be.Table 8.2
29Measuring Liquid Volumes 2. Bear in mind that the more narrow the column of liquid in the graduate, the less substantial any reading error will be. Thus for very small volume measurements a cylindrical graduate is preferable to a conical graduate.Table 8.2
30Measuring Liquid Volumes 3. Pour the liquid to be measured slowly into the graduate, watching the level of the liquid in the graduate as you do so. If the liquid is viscous, or thick, then you should attempt to pour it toward the center of the graduate to avoid having some of the liquid cling to the sides.Table 8.2
31Measuring Liquid Volumes 4. Wait for liquid clinging to the sides of the graduate to settle before taking a measurement.Table 8.2
32Measuring Liquid Volumes 5. Measure the level of the liquid at eye level and read the liquid at the bottom of the meniscus (see Figure 8.3).Table 8.2
33Measuring Liquid Volumes 6. When pouring the liquid out of the graduate, allow ample time for all of the liquid to drain. Bear in mind that depending on the viscosity of the liquid, more or less will cling to the sides of the graduate. For a particularly viscous liquid, some compensation or adjustment for this clinging may have to be made.Table 8.2
34Compounding Issues Safety Note! Use the smallest device that will hold the required volume when measuring a liquid.
35Compounding Issues Safety Note! Always measure liquids on a solid, level surface at eye level.
37PERCENTAGE OF ERRORError in measurement in pharmacy-prepared products is expected, and allowances are made for a certain percentage of error over or under the target measurement. This percent of error is considered to be a range both above and below the target measurement, and being over or under (i.e., positive or negative) within this range is not consequential.
38Compounding Issues Safety Note! Always work within the acceptable percentage of error range of your equipment.
39COMMINUTION AND BLENDING OF DRUGS Geometric Dilution Method: A way to combine drugs using a mortar and pestle.Examples of Compounding Preparations: The following are some common examples of compounding in the community pharmacy: solutions, suspensions, ointments and creams, powders, suppositories, and capsules.
40COMMINUTION AND BLENDING OF DRUGS Labeling, Record Keeping, and Cleanup: After compounding, the product must be labeled with a prescription label, and a careful record of the compounding operation should be kept. Once the compounding operation is finished, the equipment and area should be cleaned and everything should be returned to their proper places in storage.
45Compounding IssuesSafety Note!Compounding should never be rushed.
46Compounding Issues Safety Note! Regardless of their apparent stability, all suspensions should be dispensed with an auxiliary label reading “Shake Well.”
47Compounding Issues Safety Note! The qs abbreviation means to add “as much as necessary” to the specified amount. JCAHO recommends using text words rather than abbreviations to minimize a medication error.
48REFERENCE SOURCES FOR THE COMPOUNDING PHARMACY The pharmacy technician can refer to a standard reference work on the subject, such as Remington: The Science and Practice of Pharmacy by Gennaro. Another helpful source of information is a hospital pharmacy, especially a pediatrics hospital, where pharmacists have experience in compounding formulations (especially for neonates, infants, and pediatric patients).
49Terms to Remember blending Class III prescription balance comminution compounding slabcounterbalanceextemporaneous compoundingforceps
50Terms to Remember geometric dilution method good manufacturing practice (GMP)graduateslevigationmaster formula sheetmeniscusmortar and pestle
51Terms to Remember percentage of error pipette powder pulverization punch methodspatulasspatulation
52DiscussionExplain why using proper techniques and weighing ingredients with accuracy are important while preparing special compounds in the pharmacy.
53Discussion levigate f. tumbling punch method g. solute triturate The art of compounding uses a whole different language, and you have been asked to describe the following terms to a pharmacy student who is visiting your pharmacy. Use simple terms.levigatepunch methodtrituratespatulationdiluentf. tumblingg. soluteh. solventi. geometric dilutionj. comminution