Hard NAPLEX Sterile Compounding Practice Questions

Concept Explanation

Sterile compounding is the process of combining, admixing, or altering ingredients to create a sterile medication for administration via routes such as intravenous, intramuscular, or ophthalmic delivery. This practice is strictly governed by USP Chapter <797>, which establishes standards for personnel training, environmental monitoring, and beyond-use dating (BUD) to prevent patient harm from microbial contamination or incorrect dosages. Mastering this topic for the NAPLEX Prep requires a deep understanding of cleanroom engineering, ISO classification, garbing sequences, and the chemical stability of compounded sterile preparations (CSPs).

The core of sterile compounding revolves around maintaining a sterile environment, typically achieved through a Primary Engineering Control (PEC) like a Laminar Airflow Workbench (LAFW), which must maintain ISO Class 5 air quality. These units are housed within a secondary engineering control (the buffer room), which must meet ISO Class 7 standards. Pharmacists must also be proficient in calculating osmolarity, milliequivalents, and displacement volumes, especially when managing complex regimens like parenteral nutrition or oncology therapeutics. Understanding the risk levels—Category 1, Category 2, and Category 3—is essential for determining the appropriate BUD based on storage temperature and the environment in which the CSP was prepared.

Solved Examples

1. Calculate the Osmolarity: A pharmacist is preparing a 1-liter bag of D5W with 40 mEq of Potassium Chloride (KCl). What is the total osmolarity (mOsm/L) of this solution? (Molecular weight of Dextrose = 180 g/mol; KCl = 74.5 g/mol; $i$ for KCl = 2).
   1. Calculate mOsm from Dextrose: D5W means 5g/100mL, so 50g/1000mL. $$\text{mOsm/L} = \frac{50 \text{ g}}{180 \text{ g/mol}} \times 1000 = 277.7 \text{ mOsm/L}$$
   2. Calculate mOsm from KCl: $$\text{mOsm/L} = \frac{40 \text{ mEq}}{1} \times 2 = 80 \text{ mOsm/L}$$ (Note: Since mEq already accounts for valence, and KCl dissociates into 2 particles, 40 mmol of KCl provides 80 mOsm).
   3. Total: $277.7 + 80 = 357.7 \text{ mOsm/L}$.
2. Garbing Sequence: Arrange the following garbing steps in the correct order according to USP <797> standards: Gown, Shoe Covers, Gloves, Mask, Head/Hair Cover.
   1. Shoe covers (dirtiest first).
   2. Head and facial hair covers.
   3. Face mask or eye shield.
   4. Hand hygiene (30 seconds with soap and water).
   5. Non-shedding gown.
   6. Alcohol-based hand sanitizer.
   7. Sterile, powder-free gloves (tucked over gown cuffs).
3. BUD Determination: A Category 2 CSP is prepared in a cleanroom using only sterile starting components and is filtered through a 0.22-micron filter into a sterile container. If stored in a refrigerator, what is the maximum BUD?
   1. Identify the preparation: Category 2, sterile-to-sterile.
   2. Consult USP <797> BUD tables: For Category 2 CSPs prepared from sterile components and cold-sterilized, the BUD is 10 days at refrigerated temperature ($2^\circ \text{C}$ to $8^\circ \text{C}$).

Practice Questions

1. A pharmacy technician is preparing a batch of 20 sterile syringes of vancomycin in a Segregated Compounding Area (SCA). According to USP <797> standards for Category 1 CSPs, what is the maximum BUD if the syringes are stored at room temperature?

2. Calculate the volume (mL) of a 23.4% Sodium Chloride solution required to provide 75 mEq of $\text{Na}^+$ for a TPN bag. (MW of NaCl = 58.5 g/mol).

3. A laminar airflow workbench (LAFW) must be certified by an expert at least how often to ensure it maintains ISO Class 5 air quality?

4. When compounding hazardous drugs like those found in oncology therapeutics, what type of pressure must be maintained in the buffer room relative to the ante-room?

5. An IV solution contains 500 mL of D5W and 20 mEq of Magnesium Sulfate ($\text{MgSO}_4$). How many milliosmoles are in this solution? (MW of $\text{MgSO}_4$ = 120.4 g/mol; assume complete dissociation).

6. According to the NIOSH list, which of the following gown materials is preferred for compounding hazardous sterile preparations?

7. A pharmacist is performing a media-fill test to assess aseptic technique. How many days must the containers be incubated at $20^\circ \text{C}$ to $25^\circ \text{C}$ before being moved to a higher temperature incubator?

8. What is the minimum frequency for performing surface sampling in the ISO Class 5 PEC according to the latest USP <797> revisions?

9. A multidose vial (MDV) of insulin is opened on June 1st. What is the maximum BUD for this vial if stored in the refrigerator, assuming the manufacturer's expiration date is December 31st of the following year?

10. During the preparation of a CSP, a pharmacist notices the HEPA filter has been blocked by a large equipment stand. This violation of "First Air" increases the risk of what specific phenomenon?

Answers & Explanations

1. 12 hours: Category 1 CSPs are those prepared in an unclassified SCA. Regardless of the number of components or sterility of the starting material, if kept at controlled room temperature, the BUD is 12 hours. (If refrigerated, it is 24 hours).
2. 18.75 mL: First, determine the concentration of 23.4% NaCl. 23.4g/100mL = 0.234g/mL. Since $\text{mEq} = \frac{ \text{mg} \times \text{valence}}{ \text{MW}}$, then $75 = \frac{ \text{mg} \times 1}{58.5}$. Total mg needed = 4387.5 mg (or 4.3875 g). $$\text{Volume} = \frac{4.3875 \text{ g}}{0.234 \text{ g/mL}} = 18.75 \text{ mL}$$.
3. Every 6 months: All PECs (LAFWs, BSCs, CAIs) must be certified upon installation and at least every 6 months thereafter. They must also be recertified if moved or if the HEPA filter is damaged.
4. Negative pressure: To protect personnel from hazardous vapors or powders, the buffer room for hazardous compounding must be maintained at a negative pressure of at least 0.01 to 0.03 inches of water column relative to the adjacent rooms.
5. 158.8 mOsm:
   • Dextrose: $\frac{25 \text{ g}}{180 \text{ g/mol}} \times 1000 = 138.8 \text{ mOsm}$.
   • $\text{MgSO}_4$: 20 mEq of $\text{MgSO}_4$ (valence 2) is 10 mmol. Since it dissociates into 2 particles ($\text{Mg}^{2+}$ and $\text{SO}_4^{2-}$), 10 mmol = 20 mOsm.
   • Total: $138.8 + 20 = 158.8 \text{ mOsm}$.
6. Disposable, non-permeable, lint-free: For hazardous compounding (USP <800>), gowns must be disposable and shown to resist permeability by hazardous drugs (often coated with laminate).
7. 7 days: Media-fill units must be incubated at $20^\circ \text{C}$ to $25^\circ \text{C}$ for at least 7 days, followed by incubation at $30^\circ \text{C}$ to $35^\circ \text{C}$ for an additional 7 days.
8. Monthly: Under the updated USP <797> standards, surface sampling in all classified areas (including the PEC) must be performed at least monthly.
9. 28 days: Unless otherwise specified by the manufacturer, the BUD for a multidose vial after it has been punctured is 28 days.
10. Turbulence or "Zone of Turbulence": Placing items between the HEPA filter and the critical site creates turbulence, which allows contaminated room air to enter the work area, compromising the sterility of the CSP.

1. Which ISO class is required for the air inside a Primary Engineering Control (PEC)?

• AISO Class 7
• BISO Class 8
• CISO Class 5
• DISO Class 6

Frequently Asked Questions

What is the difference between Category 1 and Category 2 CSPs?

Category 1 CSPs are prepared in a segregated compounding area and have shorter beyond-use dates (typically 12-24 hours). Category 2 CSPs are prepared in a full cleanroom suite and can have significantly longer BUDs depending on sterility and storage.

How often must pharmacists undergo gloved fingertip testing?

For initial training, pharmacists must pass three successful gloved fingertip tests. After initial qualification, competency must be re-evaluated every six months for those compounding Category 2 or 3 CSPs.

Can you use a needle more than once during sterile compounding?

A needle should generally be used for a single entry into a vial or container to maintain its sharpness and sterility. However, if multiple entries into the same vial are required during a single compounding session for one patient, it may be reused if not contaminated.

What is the required temperature for a cleanroom?

The buffer and ante-rooms should be maintained at a temperature of $20^\circ \text{C}$ ($68^\circ \text{F}$) or cooler to ensure the comfort of garbed personnel and to minimize microbial growth. Humidity should be kept below 60%.

What is "First Air" in a laminar flow hood?

First Air is the undisturbed air exiting the HEPA filter that is free of contaminants. Compounding must occur within this stream of air, and nothing should block the path between the HEPA filter and the critical sites of the preparation.