NAPLEX Compounding Practice Questions with Answers

Concept Explanation

NAPLEX Compounding involves the preparation of customized medications to meet the specific needs of an individual patient, encompassing both non-sterile and sterile methodologies regulated by USP standards.

Success on the NAPLEX requires a deep understanding of USP Chapter <795> (Non-sterile Compounding), USP Chapter <797> (Sterile Compounding), and USP Chapter <800> (Hazardous Drugs). Candidates must be able to calculate precise doses using techniques like alligation, displacement values, and percentage strength adjustments. For those looking to refine their skills, using an AI Exam Simulator can help mimic the high-pressure environment of the actual board exam.

Key concepts include Beyond-Use Dates (BUD), which vary based on the water activity of the preparation and storage conditions. For instance, a water-containing oral formulation generally has a BUD of 14 days when refrigerated, while a water-containing topical formulation has a BUD of 30 days. Mastering these rules, along with the correct sequencing of garbing and the use of Primary Engineering Controls (PEC), is essential for passing the NAPLEX.

Solved Examples

Example 1: Alligation Method

A pharmacist needs to prepare 500 mL of a 15% dextrose solution using 50% dextrose and 5% dextrose. How many mL of the 50% solution are required?

1. Set up the alligation grid: Higher strength (50%) at top left, lower strength (5%) at bottom left, and target strength (15%) in the center.
2. Calculate parts: $50 - 15 = 35$ parts of the 5% solution; $15 - 5 = 10$ parts of the 50% solution.
3. Total parts: $10 + 35 = 45$ parts.
4. Calculate the volume for the 50% solution: $\frac{10}{45} \times 500 \text{ mL} = 111.1 \text{ mL}$.

Example 2: Beyond-Use Date (BUD) for Non-Sterile Compounding

A pharmacist compounds a topical cream containing hydrocortisone powder, purified water, and a commercial cream base on June 1st. What is the appropriate BUD?

1. Identify the formulation type: It is a water-containing topical/dermal semisolid formulation.
2. Apply USP <795> standards: For water-containing topical formulations, the BUD is not later than 30 days.
3. Calculate the date: June 1st + 30 days = July 1st.

Example 3: Displacement Volume

A medication vial contains 1 gram of drug powder. The instructions state to add 4.5 mL of sterile water to produce a final concentration of 200 mg/mL. What is the displacement volume of the powder?

1. Calculate the total final volume: $\frac{1000 \text{ mg}}{200 \text{ mg/mL}} = 5 \text{ mL}$.
2. Identify the volume of diluent added: 4.5 mL.
3. Calculate the displacement volume: $5 \text{ mL} - 4.5 \text{ mL} = 0.5 \text{ mL}$.

Practice Questions

1. A technician is preparing a 1:5000 solution of Potassium Permanganate. What is the percentage strength of this solution?

2. How many grams of 2% hydrocortisone ointment should be mixed with 150g of 0.5% hydrocortisone ointment to produce a 1% ointment?

3. A pharmacist is compounding an oral suspension using a manufactured tablet that expires in 6 months. If the suspension is water-containing and refrigerated, what is the BUD?

4. Which ISO class environment is required for the Primary Engineering Control (PEC) used in sterile compounding?

5. A prescription calls for 60g of a 5% salicylic acid ointment. The pharmacy has 10% salicylic acid ointment and white petrolatum. How much 10% ointment is needed?

6. According to USP <797>, how often must a person who compounds low-risk sterile products pass a media-fill test?

7. A solution contains 5 mEq of $\text{Ca}^{2+}$ per 100 mL. How many milligrams of $\text{CaCl}_2$ (MW = 111) are in 500 mL of this solution?

8. What is the minimum weighable quantity for a Class A prescription balance with a sensitivity requirement of 6 mg and an acceptable error of 5%?

9. When garbing for sterile compounding, which item should be put on first?

10. An IV bag contains 500 mL of D5W with 20 mEq of KCl. If the infusion rate is 50 mL/hr, how many mEq of KCl does the patient receive per hour?

Answers & Explanations

1. 0.02%: To convert a ratio to a percentage, divide 1 by 5000 and multiply by 100. $(1 \div 5000) \times 100 = 0.02\%$.
2. 75 grams: Using alligation: $2\% - 1\% = 1$ part of 0.5%; $1\% - 0.5\% = 0.5$ parts of 2%. The ratio is 0.5:1. If 1 part is 150g, then 0.5 parts is $150 \times 0.5 = 75 \text{g}$. For more complex math, you can use the AI Question Generator to practice similar problems.
3. 14 days: Per USP <795>, water-containing oral formulations stored at controlled cold temperatures have a BUD of 14 days, provided the ingredients do not expire sooner.
4. ISO Class 5: The PEC (e.g., laminar airflow workbench or BSC) must maintain ISO Class 5 air quality during compounding.
5. 30 grams: Using the formula $C_1V_1 = C_2V_2$: $10\% \times X = 5\% \times 60 \text{g}$. $X = 300 \div 10 = 30 \text{g}$.
6. Annually: USP <797> requires annual media-fill testing for low- and medium-risk compounding and semi-annual testing for high-risk compounding. This is a common topic in medication safety reviews.
7. 1,387.5 mg: First, find mEq in 500 mL: $5 \text{ mEq} \times 5 = 25 \text{ mEq}$. Formula: $\text{mg} = ( \text{mEq} \times \text{MW}) \div \text{Valence}$. $\text{mg} = (25 \times 111) \div 2 = 1387.5 \text{ mg}$.
8. 120 mg: $\text{MWQ} = ( \text{Sensitivity Requirement} \div \text{Acceptable Error}) \times 100$. $(6 \text{ mg} \div 5) \times 100 = 120 \text{ mg}$.
9. Shoe covers: Garbing should proceed from "dirtiest" to "cleanest." According to USP <797>, shoe covers are typically applied first, followed by head/facial hair covers, then face masks.
10. 2 mEq/hr: The concentration is $20 \text{ mEq} \div 500 \text{ mL} = 0.04 \text{ mEq/mL}$. At a rate of 50 mL/hr: $50 \text{ mL} \times 0.04 \text{ mEq/mL} = 2 \text{ mEq/hr}$. Reviewing pediatric medication calculations can also help solidify these proportional reasoning skills.

Quick Quiz

Frequently Asked Questions

What is the difference between USP <795> and USP <797>?

USP <795> provides the national standards for non-sterile compounding, such as ointments and oral suspensions, while USP <797> governs sterile compounding, including IV bags and eye drops. Both chapters focus on ensuring patient safety by preventing contamination and maintaining dosage accuracy.

How do you calculate the Beyond-Use Date for a refrigerated oral liquid?

For water-containing oral formulations, the BUD is a maximum of 14 days when stored at controlled cold temperatures. However, if any ingredient in the compound expires before those 14 days, the earlier expiration date must be used as the BUD.

What is a Primary Engineering Control (PEC)?

A PEC is a device or room that provides an ISO Class 5 environment for compounding medications. Examples include laminar airflow workbenches (LAFW), biological safety cabinets (BSC), and compounding aseptic isolators (CAI).

Why is the alligation method used in pharmacy compounding?

The alligation method is a mathematical technique used to determine the proportions of two different strengths of the same ingredient needed to reach a third, intermediate strength. It is particularly useful when mixing concentrated solutions with diluents or weaker preparations.

What are the requirements for hazardous drug compounding under USP <800>?

USP <800> requires hazardous drugs to be compounded in a negative-pressure room with external venting to protect healthcare workers. Personnel must use specific personal protective equipment (PPE), including two pairs of chemotherapy-rated gloves and specialized gowns.

What is the sensitivity requirement of a balance?

The sensitivity requirement is the minimum weight change that produces a measurable change in the balance's indicator. It is used to calculate the minimum weighable quantity to ensure that the percentage of error remains within an acceptable range, usually 5%.

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