Pharmacology: Pharmacology: Dosage Calculation Practice Questions
Test yourself on Pharmacology: Dosage Calculation with 12 original NCLEX-RN practice questions. Pick an answer to see instant feedback and a full explanation.
Free original practice questions for study purposes. Open Exam Prep is an independent study resource and is not affiliated with, endorsed by, or sponsored by the makers of NCLEX-RN.
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Answer the questions below — you get instant feedback and a full explanation for each.
1. A provider orders 500 mg of an antibiotic PO. The pharmacy supplies tablets labeled 250 mg each. How many tablets should the nurse administer?
Explanation. Use Desired/Have: 500 mg / 250 mg = 2 tablets. Always confirm whether tablets are scored if a fractional dose were needed, but here a whole-number answer results.
2. An order reads 0.125 mg of digoxin PO daily. The available elixir is 0.05 mg/mL. How many milliliters should the nurse administer?
Explanation. Desired/Have x Volume: (0.125 mg / 0.05 mg) x 1 mL = 2.5 mL. Set up units carefully so mg cancels, leaving mL.
3. A child weighs 22 lb. The order is for a drug dosed at 5 mg/kg/day in two divided doses. What is each individual dose? (1 kg = 2.2 lb)
Explanation. 22 lb / 2.2 = 10 kg. Daily dose = 10 kg x 5 mg = 50 mg/day. Divided into 2 doses = 25 mg per dose.
4. An IV of 1000 mL is to infuse over 8 hours. The tubing delivers 15 gtt/mL. What is the flow rate in gtt/min? (Round to the nearest whole drop.)
Explanation. gtt/min = (volume x drop factor) / time in minutes = (1000 x 15) / (8 x 60) = 15000/480 = 31.25, rounds to 31 gtt/min.
5. Heparin 25,000 units in 250 mL D5W is ordered to infuse at 1000 units/hr. At what rate (mL/hr) should the infusion pump be set?
Explanation. Concentration = 25,000 units / 250 mL = 100 units/mL. To give 1000 units/hr: 1000 / 100 = 10 mL/hr.
6. An order is for 1.5 g of a medication IV. The vial is labeled 500 mg/mL. How many milliliters should be drawn up?
Explanation. Convert 1.5 g to 1500 mg. Then 1500 mg / 500 mg = 3 mL. Remember 1 g = 1000 mg before calculating.
7. A medication is ordered at 2 mcg/kg/min for a patient weighing 70 kg. The drip is 400 mg in 250 mL. What is the infusion rate in mL/hr? (Round to the nearest whole number.)
Explanation. Dose = 2 mcg x 70 kg = 140 mcg/min = 8400 mcg/hr = 8.4 mg/hr. Concentration = 400 mg/250 mL = 1.6 mg/mL. Rate = 8.4/1.6 = 5.25, rounds to 5 mL/hr.
8. An order reads 60 mg PO. The bottle reads 'oral solution 100 mg per 5 mL.' How many mL should the nurse give?
Explanation. Set up ratio: 100 mg/5 mL = 60 mg/x. x = (60 x 5)/100 = 300/100 = 3 mL.
9. A patient is to receive 1 L of normal saline over 12 hours via an electronic pump. What rate (mL/hr) should the nurse program? (Round to the nearest whole number.)
Explanation. 1 L = 1000 mL. 1000 mL / 12 hr = 83.3, rounds to 83 mL/hr. Electronic pumps are programmed in mL/hr.
10. Insulin is ordered as 12 units of regular insulin subcutaneously. The vial reads U-100 (100 units/mL). The nurse should draw up which volume using a U-100 insulin syringe?
Explanation. With a U-100 insulin syringe, units are read directly on the syringe; the nurse draws to the 12-unit mark. Mathematically 12 units / 100 units/mL = 0.12 mL, but insulin is always measured in units, not by calculating mL with a regular syringe.
11. An order is for 0.6 mg of atropine IM. The ampule contains 0.4 mg/mL. How many milliliters should be administered?
Explanation. Desired/Have x Volume: (0.6 / 0.4) x 1 mL = 1.5 mL.
12. A medication's safe dose range is 10-15 mg/kg/day. A patient weighs 80 kg and the provider orders 1200 mg/day. Is this dose safe, and what is the maximum safe daily dose?
Explanation. Min = 10 x 80 = 800 mg/day; Max = 15 x 80 = 1200 mg/day. The ordered 1200 mg/day falls within (at the top of) the safe range, so it is safe to administer.
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FAQ
What formula should I rely on for most NCLEX dosage problems?
The Desired/Have x Quantity (volume) formula handles most simple problems. For IV drip rates use (volume x drop factor)/time in minutes for gtt/min, and volume/time for mL/hr. Dimensional analysis (label and cancel units) is the safest method to avoid setup errors.
Do I always need to convert units first?
Yes. Make sure the ordered dose and the available supply are in the same units before calculating (e.g., convert g to mg, mcg to mg, lb to kg). Forgetting conversions is the most common source of dosage errors on the exam.
How should I handle rounding on the NCLEX?
Follow the question's instructions. IV pump rates (mL/hr) and drop rates (gtt/min) are usually rounded to the nearest whole number. Tablets, mL by syringe, and pediatric doses may be carried to tenths or hundredths as indicated. Always include the unit label in your answer.