NCLEX dosage calculation practice questions

Write the formula, convert units first, and check if the answer makes clinical sense before you choose it.

1. Question 1

   A child who weighs 22 lb is prescribed amoxicillin 40 mg/kg/day orally, divided into 2 equal doses every 12 hours. The suspension contains 250 mg/5 mL. How many mL should the nurse give for each dose?

   • A.1.6 mL
   • B.2 mL
   • C.8 mL
   • D.4 mL
   Show answer and explanation

   Answer: D

   Step 1: 22 lb ÷ 2.2 = 10 kg. Step 2: daily dose = 40 mg/kg × 10 kg = 400 mg/day. Step 3: per dose = 400 mg ÷ 2 = 200 mg. Step 4: volume = 200 mg ÷ 250 mg × 5 mL = 4 mL. Measure with an oral syringe for accuracy.

   • A. 1.6 mL comes from dividing the daily dose by 250 (400 ÷ 250) and forgetting to multiply by 5 mL. It would deliver only 80 mg.
   • B. 2 mL contains only 100 mg, half of the dose needed.
   • C. 8 mL contains 400 mg, which is the full daily dose given at once instead of half.
   • D. Correct. 22 lb ÷ 2.2 = 10 kg. 40 mg × 10 kg = 400 mg/day. 400 ÷ 2 doses = 200 mg per dose. 200 mg ÷ 250 mg × 5 mL = 4 mL.

   Key concept: For mg/kg/day orders, find the daily total first, then divide by the number of doses.

   Tip: Per day ÷ doses per day = per dose. Do not stop at the daily total.

2. Question 2

   A client with acute decompensated heart failure who weighs 176 lb is prescribed dobutamine at 5 mcg/kg/min. The premixed bag contains dobutamine 250 mg in 250 mL. At what rate should the nurse set the pump?

   • A.0.4 mL/hour
   • B.40 mL/hour
   • C.2.4 mL/hour
   • D.24 mL/hour
   Show answer and explanation

   Answer: D

   Step 1: 176 lb ÷ 2.2 = 80 kg. Step 2: 5 mcg/kg/min × 80 kg = 400 mcg/min. Step 3: × 60 = 24,000 mcg/hour. Step 4: concentration = 250 mg ÷ 250 mL = 1 mg/mL = 1,000 mcg/mL. Step 5: 24,000 ÷ 1,000 = 24 mL/hour. The nurse monitors heart rate, rhythm and blood pressure because dobutamine can cause tachycardia and dysrhythmias.

   • A. This forgets to convert mcg/min to an hourly amount (400 ÷ 1,000).
   • B. 40 mL/hour would deliver about 8.3 mcg/kg/min.
   • C. This uses 10,000 mcg/mL as the concentration, a tenfold error.
   • D. Correct. 80 kg × 5 mcg = 400 mcg/min × 60 = 24,000 mcg/hour ÷ 1,000 mcg/mL = 24 mL/hour.

   Key concept: mcg/kg/min × kg × 60 ÷ mcg per mL = mL/hour.

   Tip: With a 1 mg/mL bag, mL/hour = mcg/kg/min × kg × 0.06.

3. Question 3

   A unit of packed red blood cells with a volume of 350 mL is to be infused over 3 hours. The blood administration set has a drop factor of 10 gtt/mL. How many drops per minute should the nurse set? Round to the nearest whole number.

   • A.19 gtt/min
   • B.117 gtt/min
   • C.12 gtt/min
   • D.29 gtt/min
   Show answer and explanation

   Answer: A

   gtt/min = volume × drop factor ÷ time in minutes. 350 mL × 10 gtt/mL = 3,500 gtt. 3 hours × 60 = 180 minutes. 3,500 ÷ 180 = 19.4, rounded to 19 gtt/min. The transfusion is started slowly for the first 15 minutes while the nurse watches for a reaction, then set to this rate, and must finish within 4 hours. This assumes the full 350 mL runs evenly over 3 hours; if the first 15 minutes run slower, the rate for the remaining volume is recalculated.

   • A. Correct. 350 mL ÷ 180 minutes × 10 gtt/mL = 19.4, rounded to 19 gtt/min.
   • B. 117 is the rate in mL/hour (350 ÷ 3 = 116.7), not drops per minute.
   • C. 12 gtt/min would deliver only about 216 mL in 3 hours.
   • D. 29 gtt/min would result from using a drop factor of 15 gtt/mL.

   Key concept: Use the blood set's drop factor (often 10 gtt/mL) when calculating gravity transfusion rates.

   Tip: Volume × drop factor ÷ minutes.

4. Question 4

   A child who weighs 33 lb has a fever. The prescription is acetaminophen 15 mg/kg orally every 6 hours as needed. The oral suspension contains 160 mg/5 mL. How many mL should the nurse give? Round to the nearest whole mL.

   • A.5 mL
   • B.7 mL
   • C.15 mL
   • D.10 mL
   Show answer and explanation

   Answer: B

   Step 1: 33 lb ÷ 2.2 = 15 kg. Step 2: 15 mg/kg × 15 kg = 225 mg. Step 3: 225 mg ÷ 160 mg × 5 mL = 7.03 mL, which rounds to 7 mL. The nurse uses an oral syringe and checks that the total does not exceed 75 mg/kg/day (1,125 mg for this child).

   • A. 5 mL contains 160 mg, which is less than the 225 mg prescribed.
   • B. Correct. 33 lb ÷ 2.2 = 15 kg. 15 mg × 15 kg = 225 mg. 225 mg ÷ 160 mg × 5 mL = 7.03 mL, rounded to 7 mL.
   • C. 15 mL contains 480 mg, which is more than double the dose.
   • D. 10 mL contains 320 mg, which is almost 100 mg more than the 225 mg dose.

   Key concept: Convert pounds to kilograms first, calculate the mg dose, then convert to mL using the concentration.

   Tip: Pounds ÷ 2.2 = kg, every time, before any mg/kg math.

5. Question 5

   A child who weighs 26.4 lb is prescribed gentamicin 45 mg IV every 8 hours. The pediatric drug reference lists a dose of 2.5 mg/kg every 8 hours. What should the nurse do?

   • A.Give the dose because it is within the safe range
   • B.Give the dose and request a trough level before the next dose
   • C.Hold the dose and contact the provider because it exceeds the recommended dose
   • D.Give 30 mg instead of 45 mg
   Show answer and explanation

   Answer: C

   Step 1: 26.4 lb ÷ 2.2 = 12 kg. Step 2: 2.5 mg/kg × 12 kg = 30 mg per dose. The prescription of 45 mg is 15 mg too high. Gentamicin is nephrotoxic and ototoxic, so an overdose in a child can cause permanent harm. The nurse holds the dose and clarifies with the provider.

   • A. The safe dose for this child is 30 mg. 45 mg is 1.5 times that amount.
   • B. A trough level does not make an overdose safe. The dose should be clarified before it is given.
   • C. Correct. 26.4 lb ÷ 2.2 = 12 kg. 2.5 mg × 12 kg = 30 mg every 8 hours. The prescribed 45 mg is too high.
   • D. The nurse cannot change a prescription independently. The provider must revise the order.

   Key concept: Always check pediatric doses against the weight-based safe range before giving them.

   Tip: Calculate, compare, clarify.