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newSchoolWorks.com › VoTechWorks › Health & Personal Services › Pharmacy Technician › Compounding: Non-Sterile, Sterile and Hazardous (USP <795>, <797>, <800>) › Lesson 2
HLT-PHAR41-04 · Lesson 2 · 15 clock hours · lab

Non-sterile equipment and technique

Objective. Use a pharmacy balance, graduates, mortar and pestle, ointment slab and spatula correctly, including geometric dilution.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed pharmacist or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Non-Sterile Compounding Equipment and Technique

Non-sterile compounding produces preparations that are not required to be sterile—creams, ointments, oral solutions, capsules, and similar dosage forms. USP Chapter <795> sets the standards that govern this work. Accurate use of equipment and sound technique are the foundation of every safe, effective compounded preparation.

The Pharmacy Balance

Two types of balances are common in non-sterile compounding. The Class A prescription balance is a mechanical torsion balance that can weigh quantities from 120 mg up to 120 g. The electronic analytical balance (often called a digital balance) is now more widely used because it is faster and reads in smaller increments. Both types must be calibrated and zeroed before each use.

Calibration steps for an electronic balance:

1. Place the balance on a level, vibration-free surface.

2. Turn it on and allow it to warm up per the manufacturer's instructions.

3. Use certified calibration weights to verify accuracy. If the display does not match the known weight, adjust according to the manufacturer's procedure and document the calibration.

4. Place weighing paper or a tared container on the pan, then press Tare (or Zero) to subtract its weight before adding ingredients.

Always weigh the minimum weighable quantity or above. For a Class A balance the minimum is 120 mg; weighing less introduces unacceptable error. For electronic balances, follow the manufacturer's stated minimum and the facility's standard operating procedures.

Safety point: Never place chemicals directly on the balance pan—always use weighing paper or a suitable container. Keep the balance clean and covered when not in use.

Graduates and Measuring Liquids

A graduate is a cylindrical or conical vessel used to measure liquid volumes. Conical graduates are easier to use for larger volumes; cylindrical graduates are more accurate for smaller volumes because the diameter is uniform.

Key rules for liquid measurement:

Safety point: After measuring, verify the correct ingredient and volume before adding it to the preparation. Mislabeled or mis-measured liquids are a leading source of compounding error.

Mortar and Pestle

The mortar and pestle is used to grind, triturate (reduce particle size), and blend powders or semisolids. Two types are used in pharmacy:

Proper technique: Use firm, circular strokes with the pestle, working from the center outward. Keep the pestle in contact with the mortar wall to ensure thorough mixing. Scrape down the sides frequently with a spatula.

Ointment Slab and Spatula

An ointment slab (also called a pill tile) is a ground-glass or porcelain flat surface used for mixing semisolids such as ointments and creams. It can also be used for levigation (incorporating a powder into a small amount of base or levigating agent to form a smooth paste before adding the bulk base).

A spatula made of stainless steel or hard plastic is used to fold, spread, and blend materials on the slab. Use a firm but controlled back-and-forth and figure-eight motion to achieve uniform mixing. Scrape all material toward the center periodically to avoid waste and to ensure complete blending.

Safety point: Some drug substances can irritate skin or mucous membranes. Wear gloves and, where required by your facility's standard operating procedures, a mask and eye protection when working with powders.

Geometric Dilution

Geometric dilution is a technique for incorporating a small quantity of a potent drug or colorant into a larger quantity of base or diluent to ensure uniform distribution. Skipping this step and simply adding all ingredients together at once can leave the active ingredient unevenly distributed—a patient safety hazard.

How to perform geometric dilution:

1. Place the smaller quantity (the active ingredient or potent substance) in the mortar.

2. Add an approximately equal volume of the diluent or base and mix thoroughly.

3. Add another equal volume of diluent and mix again.

4. Continue doubling the amount added with each step until all the diluent is incorporated.

The result is a preparation where the active ingredient is evenly dispersed throughout the final product. This technique is especially important when the active ingredient makes up a very small percentage of the total weight.

Documentation and Cleanliness

Record every compounding step in the compounding log or batch record: weights, volumes, lot numbers of ingredients, and calibration results. Clean all equipment before and after use. Residue from one preparation can contaminate the next and harm a patient.

Always verify your work with a pharmacist before the preparation leaves the compounding area. The pharmacist performs a final check; the technician's role is to prepare—not to approve the final product.

Key terms8

TareTo zero an electronic balance after placing a container or weighing paper on the pan, so that only the weight of the ingredient being added is measured.
TriturationThe process of reducing a substance to a fine powder using a mortar and pestle, or the mixing of powders together by grinding.
MeniscusThe curved surface formed by a liquid in a graduate; for most liquids, volume is read at the bottom of the curve when the graduate is held at eye level.
Geometric dilutionA stepwise mixing method in which a small quantity of an active ingredient is mixed with an equal volume of diluent, then progressively larger equal volumes are added, to achieve a uniform distribution.
LevigationThe process of incorporating a finely ground powder into a small amount of liquid or ointment base to form a smooth paste before blending into the bulk preparation.
Minimum weighable quantityThe smallest weight that can be measured on a balance within an acceptable margin of error; for a Class A prescription balance this is 120 mg.
GraduateA calibrated glass or plastic vessel—cylindrical or conical—used to measure liquid volumes in pharmacy compounding.
Ointment slabA flat, smooth ground-glass or porcelain surface used as a working area for mixing semisolid preparations such as ointments and creams.

Worked examples4

1. A formula requires 240 mg of active ingredient mixed into 4.76 g of base using geometric dilution. List the amounts added at each step.
  1. Step 1 – Start with 240 mg of active ingredient in the mortar.
  2. Step 2 – Add approximately 240 mg of base (equal volume to the active ingredient) and mix thoroughly. Running total of base added: 240 mg.
  3. Step 3 – Add approximately 480 mg of base (equal to the current mixture mass of ~480 mg) and mix thoroughly. Running total of base added: 720 mg.
  4. Step 4 – Add approximately 960 mg of base and mix thoroughly. Running total of base added: 1,680 mg.
  5. Step 5 – Add approximately 1,920 mg of base and mix thoroughly. Running total of base added: 3,600 mg.
  6. Step 6 – Add the remaining base (~1,160 mg) and mix thoroughly. Running total of base added: 4,760 mg (4.76 g). All base is now incorporated.
  7. Verify: 240 mg active + 4,760 mg base = 5,000 mg (5 g) total preparation.
Answer: Six mixing steps are needed. The active ingredient (240 mg) is diluted into 4,760 mg of base in doubling increments, yielding a uniform 5 g preparation.
2. You need to weigh 650 mg of a powder on a Class A prescription balance. Is this within the balance's usable range? What is the percent error if the balance has a sensitivity requirement of ±6 mg?
  1. Step 1 – Confirm that 650 mg is at or above the minimum weighable quantity of 120 mg. 650 mg > 120 mg, so the weight is within range.
  2. Step 2 – Calculate percent error: Percent error = (sensitivity requirement ÷ desired weight) × 100.
  3. Step 3 – Percent error = (6 mg ÷ 650 mg) × 100 = 0.92%.
  4. Step 4 – A percent error below 5% is generally considered acceptable in pharmacy compounding. 0.92% is well within that limit.
Answer: Yes, 650 mg is within the usable range. The percent error is approximately 0.92%, which is acceptable.
3. A formula calls for 8 mL of glycerin. You have a 10 mL cylindrical graduate and a 100 mL cylindrical graduate. Which should you use, and why?
  1. Step 1 – Identify the rule: always use the smallest graduate that can contain the required volume.
  2. Step 2 – The 10 mL graduate can hold 8 mL; the 100 mL graduate can also hold 8 mL.
  3. Step 3 – The 10 mL graduate has much smaller graduation markings, so reading 8 mL on it introduces far less relative error than reading 8 mL on a 100 mL graduate where each graduation represents a larger volume.
  4. Step 4 – Select the 10 mL graduate.
Answer: Use the 10 mL cylindrical graduate because it is the smallest one that holds the required 8 mL, giving the most accurate reading.
4. A compounded ointment contains 2 g of active drug in a total weight of 60 g. What is the percent strength (w/w)?
  1. Step 1 – Percent strength (w/w) = (weight of active ingredient ÷ total weight of preparation) × 100.
  2. Step 2 – Percent strength = (2 g ÷ 60 g) × 100.
  3. Step 3 – 2 ÷ 60 = 0.03333…
  4. Step 4 – 0.03333 × 100 = 3.33%.
Answer: The ointment is 3.33% (w/w).

The math in this lesson1

Learners plan geometric dilution, doubling the added base each step from 240 mg to 480 mg to 960 mg.
F-LE.2
Brush up in the math halls at newSchoolWorks.com:
In class: Balance calibration and weighing · Measuring liquids at eye level · Geometric dilution practice
Materials: Electronic balance, graduates, mortar and pestle, slab
Check: Technique checklist: competent

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Patient Safety and Quality Assurance
1. What is the minimum weighable quantity for a Class A prescription balance?
Patient Safety and Quality Assurance
2. A technician needs to measure 3 mL of a liquid. Which graduate is the best choice?
Dispensing Process
3. When reading the volume of a clear aqueous liquid in a graduate, the technician should read:
Patient Safety and Quality Assurance
4. Geometric dilution is performed primarily to:
Dispensing Process
5. A formula calls for 500 mg of powder A mixed into 7.5 g of powder B using geometric dilution. What is the correct first step?
Dispensing Process
6. Which mortar type is most appropriate for grinding hard crystalline substances to reduce their particle size?
Dispensing Process
7. A compounded cream contains 1.5 g of active ingredient in a total preparation weight of 30 g. What is the percent strength (w/w)?
Patient Safety and Quality Assurance
8. After a technician finishes compounding a non-sterile preparation, who is responsible for the final verification that the preparation is correct before it is dispensed?
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