NAPLEX Quiz: Compounding Ingredient Quantities
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Compounding Ingredient QuantitiesQuestion 1 of 20

A 30-year-old female is prescribed a compounded oral solution of potassium chloride at 10 mEq/15 mL. Prepare a total of 480 mL using purified water and a suitable sweetener q.s. ad 480 mL; the prescriber requests dye-free. If potassium chloride provides 1 mEq per 74.5 mg, using a balance and graduated cylinder, how many grams of potassium chloride are needed for the total batch?

1.19 g
11.92 g
23.84 g
0.119 g
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NAPLEX Quiz

NAPLEX Quiz: Compounding Ingredient Quantities

Practice Compounding Ingredient Quantities in NAPLEX with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Compounding Ingredient Quantities, giving you a quick way to practice the rules, question types, and explanations that matter most for NAPLEX.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A 30-year-old female is prescribed a compounded oral solution of potassium chloride at 10 mEq/15 mL. Prepare a total of 480 mL using purified water and a suitable sweetener q.s. ad 480 mL; the prescriber requests dye-free. If potassium chloride provides 1 mEq per 74.5 mg, using a balance and graduated cylinder, how many grams of potassium chloride are needed for the total batch?

  1. 1.19 g
  2. 11.92 g
  3. 23.84 g (correct answer)
  4. 0.119 g
Explanation: This question tests calculation involving milliequivalents (mEq) and unit conversions for electrolyte solutions. First, determine total mEq needed: (10 mEq/15 mL) × 480 mL = 320 mEq. Then convert to mass using the given conversion factor: 320 mEq × 74.5 mg/mEq = 23,840 mg = 23.84 g. The correct answer C (23.84 g) accurately represents this calculation. Option A (1.19 g) appears to calculate for 16 mEq instead of 320, option B (11.92 g) uses half the required amount, and option D (0.119 g) divides by 200. When working with mEq calculations, first determine total mEq needed, then use the substance-specific conversion factor. Always verify unit conversions and decimal placement in multi-step calculations.

Question 2

A 45-year-old male requires a compounded topical menthol cream at 0.5% w/w for pruritus. Prepare 200 g total using a hypoallergenic cream base q.s. ad 200 g; avoid added fragrances. Using an electronic balance and ointment slab/spatula, what quantity of menthol (in grams) is needed for this formulation?

  1. 0.1 g
  2. 1 g (correct answer)
  3. 10 g
  4. 5 g
Explanation: This question assesses calculation of API for a low-concentration weight/weight (w/w) topical preparation. For 0.5% w/w in 200 g total: (0.5 g/100 g) × 200 g = 1 g. The correct answer B (1 g) represents this accurate calculation. Option A (0.1 g) divides by 10 suggesting 0.05% strength, option C (10 g) multiplies by 10 indicating 5% strength, and option D (5 g) suggests 2.5% strength. When working with fractional percentages, convert to decimal form (0.5% = 0.005) and multiply by total weight, or use the proportion method. Always double-check calculations for low-percentage preparations as small errors can significantly impact therapeutic effect.

Question 3

A 7-year-old female (25 kg) needs an oral suspension of fluconazole 10 mg/mL, total volume 90 mL, to be dispensed in an amber bottle. You have fluconazole powder available and will QS with a vehicle. How many milligrams of fluconazole are required?

  1. 90 mg
  2. 900 mg (correct answer)
  3. 9,000 mg
  4. 450 mg
Explanation: This question assesses suspension totals. The key factor is 10 mg/mL × 90 mL = 900 mg of fluconazole. The correct answer, 900 mg, fits amber bottle. Choice A (90 mg) under by 10; choice C (9,000 mg) over by 10; choice D (450 mg) halves. Total mg = concentration × volume. Amber protects from light.

Question 4

A 38-year-old female requires a compounded mouthwash: diphenhydramine 0.5% (w/v), total volume 300 mL, sugar-free. You will prepare from diphenhydramine HCl powder and purified water using a balance and graduated cylinder. How many grams of diphenhydramine HCl are needed?

  1. 0.15 g
  2. 1.5 g (correct answer)
  3. 15 g
  4. 0.5 g
Explanation: This question tests w/v for mouthwashes. The key factor is 0.5% w/v for 300 mL: (0.5/100) × 300 = 1.5 g of diphenhydramine HCl. The correct answer, 1.5 g, is sugar-free. Choice A (0.15 g) under by 10; choice C (15 g) over by 10; choice D (0.5 g) ignores volume. Grams = (percentage/100) × mL. Sugar-free aids diabetics.

Question 5

How many grams of 10% ointment are needed to make 100 g of 8% using 2% and 10%?

  1. 25 g
  2. 50 g
  3. 75 g (correct answer)
  4. 60 g
Explanation: Use alligation: 10% and 2% must be mixed in a ratio of (8-2) to (10-8), or 6 to 2, which simplifies to 3 to 1. That means 3 parts of the total 4 parts come from the 10% ointment. For 100 g total, you need 75 g of 10% ointment. The tempting wrong answer is 25 g, but that is the amount of 2% ointment you would need, not the 10%.

Question 6

How many mL of a 1:2000 w/v solution contain 5 mg of drug?

  1. 2.5 mL
  2. 10 mL (correct answer)
  3. 5 mL
  4. 20 mL
Explanation: A 1:2000 w/v solution has 1 g (1000 mg) in 2000 mL, or 0.5 mg/mL. To get 5 mg, divide 5 mg by 0.5 mg/mL, giving 10 mL. The tempting 2.5 mL comes from misreading the ratio as 2 mg/mL rather than 0.5 mg/mL.

Question 7

How many grams of drug salt are needed to make 120 mL of a 100 mg/5 mL suspension if the salt is 75% active drug?

  1. 2.4 g
  2. 4.8 g
  3. 1.8 g
  4. 3.2 g (correct answer)
Explanation: First find the active drug needed: 100 mg/5 mL is 20 mg/mL, so 120 mL requires 2,400 mg (2.4 g) of active drug. Since the salt is only 75% active, divide by 0.75: 2,400 / 0.75 = 3,200 mg = 3.2 g. The tempting error is using 2.4 g directly, which ignores that you need extra salt to deliver that much active drug.

Question 8

How many mL of 10% w/v stock are needed to make 300 mL of 0.25% w/v?

  1. 7.5 mL (correct answer)
  2. 0.75 mL
  3. 75 mL
  4. 30 mL
Explanation: You need 0.25% x 300 mL = 0.75 g of drug; the 10% w/v stock delivers 10 g per 100 mL, or 0.1 g/mL. Dividing 0.75 g by 0.1 g/mL gives 7.5 mL. The tempting 75 mL is ten times too much and would make a 2.5% solution, not 0.25%.

Question 9

How many grams of lactose are needed for 24 capsules if each contains 25 mg drug and lactose q.s. to 200 mg?

  1. 0.6 g
  2. 4.8 g
  3. 4.2 g (correct answer)
  4. 5.4 g
Explanation: Each capsule needs 200 mg total minus 25 mg drug, so 175 mg lactose per capsule. For 24 capsules: 24 × 175 mg = 4,200 mg = 4.2 g. The tempting 4.8 g comes from using 200 mg lactose per capsule without subtracting the drug.

Question 10

A 70-year-old female needs a non-sterile oral suspension of gabapentin 50 mg/mL, total volume 180 mL, to be stored refrigerated in an amber bottle. You have gabapentin 300 mg capsules and will QS with a suitable vehicle. Using a mortar/pestle and graduated cylinder, how many grams of gabapentin are needed for the entire batch?

  1. 0.9 g
  2. 9 g (correct answer)
  3. 90 g
  4. 18 g
Explanation: This question assesses total active ingredient needs for oral suspensions from capsule contents. The key calculation is 50 mg/mL × 180 mL = 9,000 mg = 9 g of gabapentin. The correct answer, 9 g, accounts for the full batch volume accurately. Choice A (0.9 g) underestimates by a factor of 10; choice C (90 g) overestimates similarly; choice D (18 g) doubles the amount. Formula: concentration in mg/mL × volume in mL = total mg, then convert to grams if needed. Refrigerated storage enhances suspension stability.

Question 11

A pediatric patient (4-year-old male, 16 kg) needs an oral suspension of amoxicillin at 50 mg/mL. You have amoxicillin powder and will compound a total volume of 150 mL using a suitable vehicle (e.g., Ora-Plus/Ora-Sweet) q.s. ad 150 mL; label to refrigerate. Using a graduated cylinder and mortar/pestle, how many grams of amoxicillin are needed to achieve the desired concentration?

  1. 3.75 g
  2. 7.5 g (correct answer)
  3. 0.75 g
  4. 15 g
Explanation: This question evaluates the calculation of API quantity for a weight/volume (mg/mL) oral suspension preparation. The calculation requires converting the desired concentration to total drug amount: 50 mg/mL × 150 mL = 7,500 mg = 7.5 g. The correct answer B (7.5 g) represents this accurate calculation. Option A (3.75 g) incorrectly uses half the volume (75 mL), option C (0.75 g) appears to be a decimal error dividing by 10, and option D (15 g) doubles the correct amount suggesting 100 mg/mL concentration. When preparing suspensions with specific mg/mL concentrations, multiply the concentration by the total volume and convert units appropriately. Always double-check unit conversions between mg and g (1 g = 1,000 mg) to avoid medication errors.

Question 12

A 58-year-old male is prescribed compounded gabapentin capsules, 225 mg per capsule, because this strength is not commercially available. The prescription is for 90 capsules; each capsule will be filled with gabapentin powder and lactose monohydrate as the diluent. Using a capsule-filling machine and balance, how many grams of gabapentin are required for the batch (do not include any overage)?

  1. 2.025 g
  2. 20.25 g (correct answer)
  3. 202.5 g
  4. 0.2025 g
Explanation: This question tests batch calculation for solid dosage form compounding, specifically capsules with a non-standard strength. The calculation involves multiplying the per-capsule dose by the total number of capsules: 225 mg × 90 capsules = 20,250 mg = 20.25 g. The correct answer B (20.25 g) accurately reflects this calculation. Option A (2.025 g) represents a decimal placement error (divided by 10), option C (202.5 g) multiplies by 10 suggesting a unit conversion error, and option D (0.2025 g) divides by 100. When compounding batches of capsules, calculate the total API needed by multiplying individual dose by quantity, then convert to appropriate weighing units. Always verify decimal placement when converting between mg and g to ensure accurate compounding.

Question 13

A 3-year-old male (14 kg) requires an oral suspension of propranolol 4 mg/mL, total volume 75 mL. You have propranolol HCl powder available and will QS with a vehicle. Using a balance and graduated cylinder, how many milligrams of propranolol HCl are needed?

  1. 30 mg
  2. 300 mg (correct answer)
  3. 3,000 mg
  4. 75 mg
Explanation: This question assesses pediatric suspension calculations. The key factor is 4 mg/mL × 75 mL = 300 mg of propranolol HCl. The correct answer, 300 mg, matches the vehicle QS. Choice A (30 mg) under by 10; choice C (3,000 mg) over by 10; choice D (75 mg) quarters. Total mg = concentration × mL. Accurate measuring prevents dosing errors.

Question 14

A dermatologist prescribes a topical cream for a 16-year-old female: clindamycin phosphate 1% (w/w) cream, total 45 g, in an oil-in-water base. You will weigh ingredients on an electronic balance. How many grams of clindamycin phosphate are required?

  1. 0.045 g
  2. 0.45 g (correct answer)
  3. 4.5 g
  4. 45 g
Explanation: This question tests w/w concentration for topical creams. The key factor is 1% w/w of 45 g: (1/100) × 45 g = 0.45 g of clindamycin phosphate. The correct answer, 0.45 g, ensures precise formulation in the oil-in-water base. Choice A (0.045 g) is too low by a factor of 10; choice C (4.5 g) too high by 10; choice D (45 g) assumes 100%. Use: (percentage/100) × total weight = grams active. Uniform mixing is key for topical efficacy.

Question 15

A 6-year-old male (22 kg) is prescribed an oral suspension of amitriptyline 2 mg/mL, total volume 150 mL. You have amitriptyline 25 mg tablets available and will QS with a suspending vehicle. Using a mortar/pestle and graduated cylinder, how many milligrams of amitriptyline are needed for the batch?

  1. 30 mg
  2. 300 mg (correct answer)
  3. 3,000 mg
  4. 75 mg
Explanation: This question tests suspension calculations from tablets. The key factor is 2 mg/mL × 150 mL = 300 mg of amitriptyline. The correct answer, 300 mg, accounts for the full volume. Choice A (30 mg) under by 10; choice C (3,000 mg) over by 10; choice D (75 mg) quarters it. Formula: total mg = concentration × volume. Flavored vehicles mask taste for pediatrics.

Question 16

A 62-year-old male needs compounded capsules because the required dose is not commercially available: levothyroxine 37.5 mcg per capsule, quantity 90 capsules. You will compound using levothyroxine powder and lactose as filler using a capsule machine. How many milligrams of levothyroxine are required to prepare the batch (ignore overage)?

  1. 0.3375 mg
  2. 3.375 mg (correct answer)
  3. 33.75 mg
  4. 337.5 mg
Explanation: This question evaluates the total active ingredient calculation for compounded capsules with a specific dose per unit and batch quantity. The key calculation is 37.5 mcg/capsule × 90 capsules = 3,375 mcg, then 3,375 mcg ÷ 1,000 = 3.375 mg of levothyroxine. The correct answer, 3.375 mg, precisely accounts for the batch size without overage, maintaining dose accuracy. Choice A (0.3375 mg) underestimates by a factor of 10, likely a decimal error; choice C (33.75 mg) overestimates similarly; choice D (337.5 mg) multiplies by an extra factor of 10. A useful tip is to convert all units to milligrams early: total = (dose in mg) × quantity, where 37.5 mcg = 0.0375 mg, so 0.0375 × 90 = 3.375 mg. In capsule compounding, uniform filling prevents dose variability.

Question 17

A 65-year-old male with lactose intolerance needs compounded capsules: omeprazole 10 mg per capsule, quantity 100, using a lactose-free filler. Using a capsule machine and omeprazole powder, how many grams of omeprazole are required (ignore overage)?

  1. 0.1 g
  2. 1 g (correct answer)
  3. 10 g
  4. 100 g
Explanation: This question assesses capsule batch totals with fillers. The key calculation is 10 mg/capsule × 100 = 1,000 mg = 1 g of omeprazole. The correct answer, 1 g, uses lactose-free filler. Choice A (0.1 g) under by 10; choice C (10 g) over by 10; choice D (100 g) by 100. Total = dose × quantity. Allergen-free fillers prevent reactions.

Question 18

A 40-year-old male requires a compounded oral rinse: lidocaine 2% (w/v) solution, total volume 200 mL, alcohol-free. You will prepare from lidocaine HCl powder and purified water using a balance and graduated cylinder. How many grams of lidocaine HCl are needed?

  1. 0.4 g
  2. 2 g
  3. 4 g (correct answer)
  4. 20 g
Explanation: This question examines w/v calculations for oral rinses. The key factor is 2% w/v for 200 mL: (2/100) × 200 = 4 g of lidocaine HCl. The correct answer, 4 g, provides the alcohol-free solution accurately. Choice A (0.4 g) undercalculates by 10; choice B (2 g) halves the volume; choice D (20 g) overestimates by 5. Formula: grams = (percentage/100) × volume in mL. Alcohol-free bases improve patient tolerance.

Question 19

A pediatric patient (2-year-old female, 12 kg) needs an oral suspension of metronidazole 25 mg/mL, total volume 100 mL. You have metronidazole benzoate powder available and will QS with a flavored vehicle. Using a balance and graduated cylinder, how many grams of metronidazole are needed?

  1. 0.25 g
  2. 2.5 g (correct answer)
  3. 25 g
  4. 250 g
Explanation: This question evaluates concentration calculations for pediatric oral suspensions. The key calculation is 25 mg/mL × 100 mL = 2,500 mg = 2.5 g of metronidazole. The correct answer, 2.5 g, matches the direct computation for the flavored vehicle. Choice A (0.25 g) underestimates by 10; choice C (25 g) overestimates by 10; choice D (250 g) by 100. Formula: total active = concentration × volume. Note potential need for equivalent adjustments if using salts like benzoate.

Question 20

A 47-year-old male needs compounded capsules: baclofen 7.5 mg per capsule, quantity 120 capsules, because 7.5 mg strength is unavailable. You will use baclofen powder with a capsule-filling machine. How many grams of baclofen are required for the batch (ignore overage)?

  1. 0.09 g
  2. 0.9 g (correct answer)
  3. 9 g
  4. 90 g
Explanation: This question evaluates capsule batch for unavailable doses. The key calculation is 7.5 mg/capsule × 120 = 900 mg = 0.9 g of baclofen. The correct answer, 0.9 g, ignores overage. Choice A (0.09 g) under by 10; choice C (9 g) over by 10; choice D (90 g) by 100. Total = dose × quantity. Machines ensure uniformity.