Pharmacology Quiz: Dose Calculations Concentration
20 questions · exam conditions
0:00
Dose Calculations ConcentrationQuestion 1 of 20

Dilute 5 mL of 20 mg/mL stock to 25 mL. Volume (mL) for 60 mg?

15 mL
3 mL
18 mL
75 mL
← Back to quizzes

Pharmacology Quiz

Pharmacology Quiz: Dose Calculations Concentration

Practice Dose Calculations Concentration in Pharmacology 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 Dose Calculations Concentration, giving you a quick way to practice the rules, question types, and explanations that matter most for Pharmacology.

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

Dilute 5 mL of 20 mg/mL stock to 25 mL. Volume (mL) for 60 mg?

  1. 15 mL (correct answer)
  2. 3 mL
  3. 18 mL
  4. 75 mL
Explanation: First find the diluted concentration: 5 mL of 20 mg/mL gives 100 mg, and diluting to 25 mL makes 100 mg / 25 mL = 4 mg/mL. To get 60 mg at 4 mg/mL, divide 60 by 4 to get 15 mL. The tempting error is using the original 20 mg/mL and calculating 60 / 20 = 3 mL, which ignores the dilution step.

Question 2

A 0.25 mg/mL solution is available. How many mL for 500 mcg?

  1. 2000 mL
  2. 0.5 mL
  3. 0.125 mL
  4. 2.0 mL (correct answer)
Explanation: Since 500 mcg equals 0.5 mg, divide the needed dose by the concentration: 0.5 mg / 0.25 mg/mL = 2 mL. The tempting wrong answer is 0.5 mL because it mistakes 0.5 mg for a volume instead of applying the 0.25 mg/mL strength.

Question 3

How many mL of a 2% w/v solution provides 40 mg?

  1. 20 mL
  2. 0.2 mL
  3. 2 mL (correct answer)
  4. 4 mL
Explanation: A 2% w/v solution contains 2 g per 100 mL, which equals 2000 mg per 100 mL or 20 mg per mL. To get 40 mg, divide 40 by 20, giving 2 mL. The tempting error is 20 mL, which incorrectly treats 2% as 2 mg per mL instead of 20 mg per mL.

Question 4

Give 0.1 mL/kg of 10 mg/mL solution. Patient weighs 25 kg. Dose (mg)?

  1. 2.5 mg
  2. 25 mg (correct answer)
  3. 10 mg
  4. 250 mg
Explanation: First find the volume to give: 0.1 mL/kg times 25 kg equals 2.5 mL. Then multiply by the concentration: 2.5 mL times 10 mg/mL equals 25 mg. The tempting wrong answer is 250 mg, which skips the 0.1 mL/kg factor and just multiplies 10 mg by 25 kg.

Question 5

16 kg child: 0.75 mg/kg/day divided q8h. Concentration is 2 mg/mL. mL/dose?

  1. 2 mL (correct answer)
  2. 6 mL
  3. 4 mL
  4. 12 mL
Explanation: Calculate the total daily dose: 0.75 mg/kg/day times 16 kg = 12 mg/day. Divide by 3 doses per day because q8h means every 8 hours, giving 4 mg per dose. At 2 mg/mL, each dose is 4 divided by 2 = 2 mL. The tempting error is using 6 mL as the daily volume without dividing by 3.

Question 6

An order is written to add 80 mEq of potassium chloride (KCl) to a 1 L bag of 0.9% sodium chloride. The pharmacy stocks KCl in vials with a concentration of 2 mEq/mL. What volume of the KCl solution must be added to the IV bag?

  1. 4 mL
  2. 16 mL
  3. 40 mL (correct answer)
  4. 80 mL
Explanation: This is a direct calculation of volume from a required dose and a given concentration. The volume of the IV bag (1 L) is extraneous information for this specific question. The required dose is 80 mEq and the concentration of the stock solution is 2 mEq/mL. Calculate the volume to add: 80 mEq÷2 mEq/mL=40 mL80 \text{ mEq} \div 2 \text{ mEq/mL} = 40 \text{ mL}.

Question 7

An order is written to prepare a dopamine infusion by adding 400 mg of dopamine to 250 mL of D5W. The pharmacy stocks dopamine in a 10 mL vial with a concentration of 80 mg/mL. What volume of the dopamine stock solution should be added to the D5W bag?

  1. 5.0 mL (correct answer)
  2. 6.25 mL
  3. 8.0 mL
  4. 10.0 mL
Explanation: The question asks for the volume of the stock solution to add to the IV bag. The key is to use the desired dose (400 mg) and the concentration of the stock vial (80 mg/mL). The volume of the IV bag (250 mL) and the volume of the stock vial (10 mL) are distractors for this step. The calculation is: 400 mg÷80 mg/mL=5.0 mL400 \text{ mg} \div 80 \text{ mg/mL} = 5.0 \text{ mL}.

Question 8

An IV infusion of 100 mL of normal saline contains 2 g of magnesium sulfate. A bolus of 500 mg of magnesium sulfate is ordered. What volume from the IV bag should be administered for the bolus?

  1. 12.5 mL
  2. 20.0 mL
  3. 25.0 mL (correct answer)
  4. 50.0 mL
Explanation: First, determine the concentration of magnesium sulfate in the IV bag in mg/mL. Convert the total drug amount to mg: 2 g=2000 mg2 \text{ g} = 2000 \text{ mg}. Calculate the concentration: 2000 mg÷100 mL=20 mg/mL2000 \text{ mg} \div 100 \text{ mL} = 20 \text{ mg/mL}. Next, calculate the volume needed for the 500 mg bolus dose: 500 mg÷20 mg/mL=25.0 mL500 \text{ mg} \div 20 \text{ mg/mL} = 25.0 \text{ mL}.

Question 9

The pharmacy has a 2 g vial of vancomycin powder. The instructions on the vial state:

  • For IV intermittent infusion, reconstitute with 20 mL of Sterile Water for Injection.
  • The resulting solution will have a concentration of 100 mg/mL.
  • Further dilute the required dose in at least 200 mL of a compatible IV fluid.

A patient weighing 80 kg is prescribed vancomycin 15 mg/kg IV. Based on the information in the passage, what volume of the reconstituted solution is needed before further dilution?

  1. 10 mL
  2. 20 mL
  3. 15 mL
  4. 12 mL (correct answer)
Explanation: When you encounter dosage calculations in pharmacology, you need to work systematically through three key values: the patient's dose requirement, the concentration of your prepared solution, and the volume needed from that solution. First, calculate the total dose needed for this 80 kg patient: 80 kg×15 mg/kg=1200 mg80 \text{ kg} \times 15 \text{ mg/kg} = 1200 \text{ mg} Next, determine how much reconstituted solution contains this dose. The passage tells you that after reconstitution, the concentration is 100 mg/mL. Using the formula: Volume = Dose ÷ Concentration, you get: 1200 mg100 mg/mL=12 mL\frac{1200 \text{ mg}}{100 \text{ mg/mL}} = 12 \text{ mL} Therefore, D) 12 mL is correct. Here's why the other options are wrong: A) 10 mL would only provide 1000 mg of vancomycin (10 mL × 100 mg/mL), which is 200 mg short of the required dose. B) 20 mL represents the total volume of diluent used for reconstitution, not the volume needed for the patient's dose—this would deliver 2000 mg, significantly overdosing the patient. C) 15 mL might seem tempting since it matches the mg/kg dose, but this would provide 1500 mg of vancomycin, which is 300 mg more than needed. The key strategy here is to never skip the dose calculation step, even when the numbers seem to align coincidentally. Always calculate the patient's total dose first, then determine the volume needed based on the final concentration after reconstitution.

Question 10

A patient receives a daily 750 mg dose of an antibiotic. The medication is supplied in a 20 mL multi-dose vial with a concentration of 300 mg/mL. How many full daily doses can be obtained from one vial?

  1. 7 doses
  2. 8 doses (correct answer)
  3. 9 doses
  4. 10 doses
Explanation: First, calculate the total amount of medication in the vial: 20 mL×300 mg/mL=6000 mg20 \text{ mL} \times 300 \text{ mg/mL} = 6000 \text{ mg}. Next, divide the total amount of medication by the amount per dose to find the number of doses: 6000 mg÷750 mg/dose=8 doses6000 \text{ mg} \div 750 \text{ mg/dose} = 8 \text{ doses}. Since the result is a whole number, 8 full doses can be obtained.

Question 11

An order is written to prepare a dopamine infusion by adding 400 mg of dopamine to 250 mL of D5W. The pharmacy stocks dopamine in a 10 mL vial with a concentration of 80 mg/mL. What volume of the dopamine stock solution should be added to the D5W bag?

  1. 5.0 mL (correct answer)
  2. 6.25 mL
  3. 8.0 mL
  4. 10.0 mL
Explanation: The question asks for the volume of the stock solution to add to the IV bag. The key is to use the desired dose (400 mg) and the concentration of the stock vial (80 mg/mL). The volume of the IV bag (250 mL) and the volume of the stock vial (10 mL) are distractors for this step. The calculation is: 400 mg÷80 mg/mL=5.0 mL400 \text{ mg} \div 80 \text{ mg/mL} = 5.0 \text{ mL}.

Question 12

A pharmacist needs to prepare a 100 mL solution of a medication with a final concentration of 2 mg/mL. The available stock solution has a concentration of 5% w/v. How many milliliters of the stock solution are required?

  1. 4.0 mL (correct answer)
  2. 10.0 mL
  3. 25.0 mL
  4. 40.0 mL
Explanation: This is a dilution calculation requiring a concentration conversion. First, convert the stock solution's concentration from % w/v to mg/mL. 5% w/v means 5 g/100 mL. 5 g=5000 mg5 \text{ g} = 5000 \text{ mg}, so the concentration is 5000 mg/100 mL=50 mg/mL5000 \text{ mg} / 100 \text{ mL} = 50 \text{ mg/mL} (C1). The desired final concentration is 2 mg/mL (C2) and the final volume is 100 mL (V2). Use the dilution formula C1V1=C2V2C_1V_1 = C_2V_2: (50 mg/mL)×V1=(2 mg/mL)×(100 mL)(50 \text{ mg/mL}) \times V_1 = (2 \text{ mg/mL}) \times (100 \text{ mL}). Solving for V1 gives V1=200/50=4.0 mLV_1 = 200 / 50 = 4.0 \text{ mL}.

Question 13

A patient is to receive a loading dose of 1 g of phenytoin. The available concentration is 50 mg/mL. To minimize adverse effects, the total volume must be split into three equal doses administered 2 hours apart. What is the volume of each individual dose?

  1. 6.7 mL (correct answer)
  2. 10.0 mL
  3. 16.7 mL
  4. 20.0 mL
Explanation: First, convert the total dose from grams to milligrams: 1 g=1000 mg1 \text{ g} = 1000 \text{ mg}. Next, calculate the total volume required for the loading dose: 1000 mg÷50 mg/mL=20 mL1000 \text{ mg} \div 50 \text{ mg/mL} = 20 \text{ mL}. Finally, divide the total volume by three to find the volume of each individual dose: 20 mL÷3=6.66... mL20 \text{ mL} \div 3 = 6.66... \text{ mL}, which rounds to 6.7 mL.

Question 14

A patient in anaphylactic shock requires an intramuscular injection of 0.3 mg of epinephrine. The available stock is a vial labeled "Epinephrine 1:1000". What volume should be drawn into the syringe for administration?

  1. 0.03 mL
  2. 0.3 mL (correct answer)
  3. 3 mL
  4. 30 mL
Explanation: First, interpret the ratio concentration. A 1:1000 ratio means 1 gram of solute per 1000 mL of solvent. Convert grams to milligrams: 1 g=1000 mg1 \text{ g} = 1000 \text{ mg}. Therefore, the concentration is 1000 mg/1000 mL, which simplifies to 1 mg/mL. Next, calculate the volume required for the 0.3 mg dose: 0.3 mg÷1 mg/mL=0.3 mL0.3 \text{ mg} \div 1 \text{ mg/mL} = 0.3 \text{ mL}.

Question 15

The pharmacy has a 2 g vial of vancomycin powder. The instructions on the vial state:

  • For IV intermittent infusion, reconstitute with 20 mL of Sterile Water for Injection.
  • The resulting solution will have a concentration of 100 mg/mL.
  • Further dilute the required dose in at least 200 mL of a compatible IV fluid.

A patient weighing 80 kg is prescribed vancomycin 15 mg/kg IV. Based on the information in the passage, what volume of the reconstituted solution is needed before further dilution?

  1. 10 mL
  2. 20 mL
  3. 15 mL
  4. 12 mL (correct answer)
Explanation: When you encounter dosage calculations in pharmacology, you need to work systematically through three key values: the patient's dose requirement, the concentration of your prepared solution, and the volume needed from that solution. First, calculate the total dose needed for this 80 kg patient: 80 kg×15 mg/kg=1200 mg80 \text{ kg} \times 15 \text{ mg/kg} = 1200 \text{ mg} Next, determine how much reconstituted solution contains this dose. The passage tells you that after reconstitution, the concentration is 100 mg/mL. Using the formula: Volume = Dose ÷ Concentration, you get: 1200 mg100 mg/mL=12 mL\frac{1200 \text{ mg}}{100 \text{ mg/mL}} = 12 \text{ mL} Therefore, D) 12 mL is correct. Here's why the other options are wrong: A) 10 mL would only provide 1000 mg of vancomycin (10 mL × 100 mg/mL), which is 200 mg short of the required dose. B) 20 mL represents the total volume of diluent used for reconstitution, not the volume needed for the patient's dose—this would deliver 2000 mg, significantly overdosing the patient. C) 15 mL might seem tempting since it matches the mg/kg dose, but this would provide 1500 mg of vancomycin, which is 300 mg more than needed. The key strategy here is to never skip the dose calculation step, even when the numbers seem to align coincidentally. Always calculate the patient's total dose first, then determine the volume needed based on the final concentration after reconstitution.

Question 16

A patient is prescribed 40 mg of furosemide IV. The medication is available in a solution of 10 mg/mL. The medication is to be diluted in 50 mL of normal saline and infused over 15 minutes. What volume of the furosemide solution should be drawn from the vial to be added to the normal saline?

  1. 0.4 mL
  2. 2.5 mL
  3. 4.0 mL (correct answer)
  4. 10.0 mL
Explanation: The question asks for the volume of furosemide solution to be drawn from the vial. The information about dilution volume (50 mL) and infusion time (15 minutes) is not needed for this calculation. The required dose is 40 mg, and the available concentration is 10 mg/mL. The calculation is: 40 mg÷10 mg/mL=4.0 mL40 \text{ mg} \div 10 \text{ mg/mL} = 4.0 \text{ mL}.

Question 17

A pharmacist needs to prepare an oral suspension for a child prescribed 45 mg of amoxicillin. The stock bottle is a powder that, when reconstituted, has a final concentration of 125 mg per 5 mL. What volume, in mL, should the pharmacist instruct the parent to administer per dose?

  1. 1.4 mL
  2. 1.8 mL (correct answer)
  3. 2.2 mL
  4. 2.8 mL
Explanation: First, determine the concentration in mg/mL. The concentration is 125 mg per 5 mL, so 125 mg÷5 mL=25 mg/mL125 \text{ mg} \div 5 \text{ mL} = 25 \text{ mg/mL}. Next, calculate the volume needed for the 45 mg dose: 45 mg÷25 mg/mL=1.8 mL45 \text{ mg} \div 25 \text{ mg/mL} = 1.8 \text{ mL}.

Question 18

A patient is ordered to receive 250 mcg of digoxin IV push. The available stock solution has a concentration of 0.5 mg/mL. What is the correct volume to administer?

  1. 0.05 mL
  2. 0.5 mL (correct answer)
  3. 1.25 mL
  4. 5.0 mL
Explanation: This calculation requires a unit conversion. First, convert the ordered dose from micrograms (mcg) to milligrams (mg): 250 mcg÷1000 mcg/mg=0.25 mg250 \text{ mcg} \div 1000 \text{ mcg/mg} = 0.25 \text{ mg}. Then, calculate the volume to administer using the available concentration: 0.25 mg÷0.5 mg/mL=0.5 mL0.25 \text{ mg} \div 0.5 \text{ mg/mL} = 0.5 \text{ mL}.

Question 19

A patient requires a local anesthetic block and is prescribed 75 mg of bupivacaine. The medication is available as a 0.5% solution. How many milliliters of the solution are required to deliver the correct dose?

  1. 1.5 mL
  2. 3.75 mL
  3. 15 mL (correct answer)
  4. 37.5 mL
Explanation: First, convert the percentage concentration to mg/mL. A 0.5% solution means 0.5 g per 100 mL. Convert grams to milligrams: 0.5 g=500 mg0.5 \text{ g} = 500 \text{ mg}. So, the concentration is 500 mg/100 mL, which simplifies to 5 mg/mL. Then, calculate the volume needed for the 75 mg dose: 75 mg÷5 mg/mL=15 mL75 \text{ mg} \div 5 \text{ mg/mL} = 15 \text{ mL}.

Question 20

An order is written to add 80 mEq of potassium chloride (KCl) to a 1 L bag of 0.9% sodium chloride. The pharmacy stocks KCl in vials with a concentration of 2 mEq/mL. What volume of the KCl solution must be added to the IV bag?

  1. 4 mL
  2. 16 mL
  3. 40 mL (correct answer)
  4. 80 mL
Explanation: This is a direct calculation of volume from a required dose and a given concentration. The volume of the IV bag (1 L) is extraneous information for this specific question. The required dose is 80 mEq and the concentration of the stock solution is 2 mEq/mL. Calculate the volume to add: 80 mEq÷2 mEq/mL=40 mL80 \text{ mEq} \div 2 \text{ mEq/mL} = 40 \text{ mL}.