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Pharmacological and Parenteral Therapies

NCLEX Dosage Calculation Practice Questions

Quick answer

Dosage calculation questions test whether you can turn a provider order into a safe, measurable dose using the supply on hand. They sit under Pharmacological and Parenteral Therapies (13 to 19 percent of the exam) and usually appear as fill-in-the-blank items, so there is no multiple choice to lean on.

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Most students know the formulas. What trips them up is the setup: writing the order and the supply in different units and never noticing, or rounding halfway through instead of at the end. The exam also likes to bury the weight in pounds when the order is in mg/kg, so the first thing to do with every calculation is line up the units before you touch a number. Work each problem on paper the way you would at the medication cart, label every step, and check the final answer against common sense (0.4 mL of morphine is believable, 40 mL is not). The questions below cover every calculation type the NCLEX draws from, and each rationale shows the full working so you can see exactly where a wrong answer comes from.

Practice questions

1

A client with postoperative pain has an order for morphine 4 mg IV push. The vial on hand is labeled 10 mg/mL. How many mL should the nurse draw up?

  1. A0.25 mL
  2. B0.4 mL
  3. C2.5 mL
  4. D4 mL
Show answer

Answer: B

Use desired dose divided by dose on hand, times the volume: 4 mg divided by 10 mg equals 0.4, times 1 mL equals 0.4 mL. Draw up 0.4 mL in a 1 mL syringe so the measurement is accurate.

Why the others are wrong

0.25 mL would deliver 2.5 mg, which underdoses the client. 2.5 mL comes from flipping the fraction (10 divided by 4) and would deliver 25 mg, a dangerous overdose. 4 mL ignores the concentration entirely and would deliver 40 mg.

2

A client is ordered metoprolol tartrate 75 mg PO twice daily. The pharmacy supplies 50 mg scored tablets. How many tablets should the nurse give per dose?

  1. A0.5 tablet
  2. B1 tablet
  3. C1.5 tablets
  4. D2 tablets
Show answer

Answer: C

Desired 75 mg divided by on hand 50 mg equals 1.5 tablets. The tablet is scored, so giving one whole tablet plus one half is acceptable.

Why the others are wrong

0.5 tablet is 25 mg, one third of the order. 1 tablet is 50 mg and leaves the client 25 mg short. 2 tablets is 100 mg, 25 mg over the ordered dose.

3

The nurse is to infuse 1,000 mL of 0.9% sodium chloride over 8 hours by gravity. The tubing drop factor is 15 gtt/mL. At how many gtt/min should the nurse set the drip?

  1. A21 gtt/min
  2. B31 gtt/min
  3. C42 gtt/min
  4. D125 gtt/min
Show answer

Answer: B

Convert hours to minutes first: 8 hours equals 480 minutes. Then total volume times drop factor divided by minutes: 1,000 mL times 15 gtt/mL equals 15,000 gtt, divided by 480 minutes equals 31.25, rounded to 31 gtt/min. Drops are always rounded to a whole number because you cannot count a fraction of a drop.

Why the others are wrong

21 gtt/min is the answer with a 10 gtt/mL drop factor, not 15. 42 gtt/min is the answer with a 20 gtt/mL set. 125 is the mL/hr rate, not drops per minute, and would run the bag in far too fast on this tubing.

4

Ceftriaxone 1 g in 100 mL of 0.9% sodium chloride is ordered to infuse over 30 minutes through an infusion pump. At what rate in mL/hr should the nurse program the pump?

  1. A50 mL/hr
  2. B100 mL/hr
  3. C150 mL/hr
  4. D200 mL/hr
Show answer

Answer: D

Pumps are set in mL per hour, so convert the time: 100 mL divided by 30 minutes equals 3.33 mL/min, times 60 minutes equals 200 mL/hr. A shortcut is 100 mL divided by 0.5 hour equals 200 mL/hr. The pump will run for 30 minutes and then alarm when the 100 mL is complete.

Why the others are wrong

50 mL/hr would take 2 hours to deliver the dose. 100 mL/hr is the common error of entering the bag volume as the rate, which doubles the infusion time to 1 hour. 150 mL/hr delivers the dose in 40 minutes, which is not what was ordered.

5

A client who weighs 176 lb is ordered enoxaparin 1 mg/kg subcutaneously every 12 hours. The prefilled syringes on hand are 100 mg/mL. How many mg should the nurse give per dose?

  1. A80 mg
  2. B88 mg
  3. C160 mg
  4. D176 mg
Show answer

Answer: A

Convert pounds to kilograms by dividing by 2.2: 176 lb divided by 2.2 equals 80 kg. Then 1 mg/kg times 80 kg equals 80 mg per dose, which is 0.8 mL from the 100 mg/mL syringe.

Why the others are wrong

88 mg comes from dividing by 2 instead of 2.2, a very common slip. 160 mg is the 24 hour total, not the per-dose amount. 176 mg treats the weight in pounds as if it were kilograms, which more than doubles the dose.

6

A client is ordered levothyroxine 0.075 mg PO daily. The tablets available are 25 mcg each. How many tablets should the nurse administer?

  1. A0.3 tablet
  2. B1 tablet
  3. C3 tablets
  4. D30 tablets
Show answer

Answer: C

Convert the order to the same unit as the supply. 1 mg equals 1,000 mcg, so 0.075 mg times 1,000 equals 75 mcg. Then 75 mcg divided by 25 mcg per tablet equals 3 tablets.

Why the others are wrong

0.3 tablet is what you get if you forget to convert and divide 0.075 by 0.25. 1 tablet would give only 25 mcg, one third of the dose. 30 tablets comes from moving the decimal one place too far (750 mcg) and would be a tenfold overdose.

7

A 44 lb child is prescribed ibuprofen 250 mg PO every 6 hours as needed for fever. The drug reference lists the safe dose as 5 to 10 mg/kg/dose. Which action should the nurse take first?

  1. AGive the dose as ordered because it is within the safe range
  2. BGive half the dose and document the reason
  3. CHold the dose and contact the provider because the dose exceeds the safe range
  4. DGive the dose and recheck the temperature in 1 hour
Show answer

Answer: C

Convert the weight: 44 lb divided by 2.2 equals 20 kg. Safe range: 5 mg times 20 kg equals 100 mg, and 10 mg times 20 kg equals 200 mg per dose. The ordered 250 mg is above the 200 mg upper limit, so the nurse holds it and calls the provider for a corrected order.

Why the others are wrong

The dose is not within range, so giving it as ordered is unsafe. A nurse cannot change a prescribed dose independently, so giving half is practicing outside scope. Giving the dose and rechecking the temperature still delivers an overdose.

8

A client is receiving a heparin infusion from a bag labeled 25,000 units in 250 mL of D5W. The order is heparin 1,400 units/hr. At what rate in mL/hr should the nurse set the pump?

  1. A5.6 mL/hr
  2. B11 mL/hr
  3. C14 mL/hr
  4. D56 mL/hr
Show answer

Answer: C

Find the concentration first: 25,000 units divided by 250 mL equals 100 units/mL. Then 1,400 units/hr divided by 100 units/mL equals 14 mL/hr. Always double check heparin rates with a second nurse because it is a high alert medication.

Why the others are wrong

5.6 mL/hr would deliver only 560 units/hr. 11 mL/hr delivers 1,100 units/hr, which is under the order. 56 mL/hr delivers 5,600 units/hr, four times the ordered dose and a serious bleeding risk.

9

At 0900 the nurse hangs a 500 mL bag of lactated Ringer's at 80 mL/hr on an infusion pump. At what time should the nurse expect the bag to be finished?

  1. A1300
  2. B1515
  3. C1530
  4. D1700
Show answer

Answer: B

Time equals volume divided by rate: 500 mL divided by 80 mL/hr equals 6.25 hours. Convert the fraction of an hour to minutes: 0.25 times 60 equals 15 minutes, so the infusion takes 6 hours 15 minutes. 0900 plus 6 hours 15 minutes equals 1515.

Why the others are wrong

1300 would require a rate of 125 mL/hr. 1530 is the result of reading 0.25 hours as 30 minutes, a very common slip. 1700 would be an 8 hour infusion, which matches a rate of 62.5 mL/hr.

10

A parent is being discharged with a prescription for cephalexin oral suspension 375 mg PO every 8 hours for their child. The bottle is labeled 250 mg/5 mL. Which statement by the parent shows correct understanding of the teaching?

  1. A"I will give 5 mL with the oral syringe three times a day."
  2. B"I will give one and a half teaspoons from our kitchen spoon set."
  3. C"I will give 7.5 mL with the oral syringe three times a day."
  4. D"I will give 12.5 mL with the oral syringe three times a day."
Show answer

Answer: C

Desired 375 mg divided by on hand 250 mg equals 1.5, times 5 mL equals 7.5 mL per dose. Every 8 hours is three doses a day, and an oral syringe or dosing cup gives an accurate measurement.

Why the others are wrong

5 mL delivers only 250 mg per dose. One and a half teaspoons is the right volume on paper, but household spoons vary widely in size, so teaching must direct the parent to a marked oral syringe. 12.5 mL delivers 625 mg, well over the ordered dose.

Quick tips

  • Write the order and the supply side by side and convert them to the same unit before you do anything else. Most wrong answers on this topic are unit errors, not math errors.
  • Divide pounds by 2.2 to get kilograms. Dividing by 2 looks close but changes a mg/kg dose by 10 percent, which is enough to fail a question.
  • Round only at the final step. For gtt/min round to a whole number. For mL on a 1 mL syringe you can go to two decimal places (0.4 mL), and for mL/hr on a pump go to a whole number unless the facility allows tenths.
  • Sanity check the answer against the dosage form. More than 3 tablets, more than 1 mL into a child's thigh, or a heparin rate over 30 mL/hr should make you redo the math.
  • For every pediatric order, calculate the safe range in mg per dose first, then compare the order to it. Knowing the dose is too high is only half the question; the exam wants you to hold it and call the provider.

Related topics

FAQ

How many dosage calculation questions are on the NCLEX?

There is no fixed number. Most candidates report between 2 and 6 fill-in-the-blank calculations in a single exam, and they are spread across pharmacology, IV therapy and pediatrics rather than grouped together.

Can I use a calculator on the NCLEX for dosage questions?

Yes. An on-screen calculator is built into the exam for every fill-in-the-blank item. You still need to set the problem up yourself, and the exam tells you how to round, so read that instruction before you type the answer.

What is the easiest formula for dosage calculations?

Desired dose divided by dose on hand, times the volume it comes in, covers most oral and injectable problems. For IV rates use volume divided by time (in hours for mL/hr, in minutes with the drop factor for gtt/min). Dimensional analysis works just as well if you prefer it; pick one method and use it every time.

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