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Here's a comprehensive set of drug calculation examples covering all major types tested in nursing exams:

Nursing Drug Calculation Examples - All Types

TYPE 1: Oral Tablet/Capsule Dosage

Formula: Dose required ÷ Dose available × Tablet strength

Question: A patient is prescribed Amoxicillin 750 mg orally. On hand you have Amoxicillin 250 mg capsules. How many capsules should you administer?

Solution:

Tablets to give = (Dose ordered ÷ Dose on hand) × Quantity on hand

= (750 mg ÷ 250 mg) × 1 capsule

= 3 capsules ✅

TYPE 2: Oral Liquid Dosage

Formula: (Dose ordered ÷ Dose on hand) × Volume on hand

Question: A doctor orders Paracetamol 375 mg oral suspension. The bottle reads 250 mg per 5 mL. How many mL should you give?

Solution: = (375 ÷ 250) × 5 mL

= 1.5 × 5

= 7.5 mL ✅

TYPE 3: Weight-Based Dosage (mg/kg)

Formula: Dose per kg × Patient's weight = Total dose required

Question: A child weighs 24 kg. The doctor orders Gentamicin 2.5 mg/kg IV. How many mg should be given?

Solution: = 2.5 mg/kg × 24 kg

= 60 mg ✅

Follow-up: The vial contains 40 mg/mL. How many mL do you draw up?

= (60 ÷ 40) × 1 mL = 1.5 mL ✅

TYPE 4: IV Flow Rate (mL/hr)

Formula: Volume (mL) ÷ Time (hours) = Flow rate (mL/hr)

Question: A patient is to receive 1,000 mL of Normal Saline over 8 hours. What should the IV pump be set at in mL/hr?

Solution: = 1,000 mL ÷ 8 hours

= 125 mL/hr ✅

TYPE 5: IV Drop Rate (drops/min)

Formula: (Volume in mL × Drop factor) ÷ Time in minutes = drops/min

Question: Infuse 500 mL of Dextrose 5% over 4 hours using a giving set with a drop factor of 20 drops/mL. Calculate the drip rate in drops per minute.

Solution: Time in minutes = 4 × 60 = 240 minutes

= (500 × 20) ÷ 240

= 10,000 ÷ 240

= 41.67 ≈ 42 drops/min ✅

TYPE 6: IV Concentration / Drug in Solution

Formula: (Dose ordered ÷ Concentration available) × Volume = mL to give

Question: A patient requires Dopamine 400 mcg/min IV. The bag contains 800 mg of Dopamine in 250 mL of D5W. At what rate (mL/hr) should the infusion run?

Step 1 - Find concentration: 800 mg = 800,000 mcg in 250 mL Concentration = 800,000 ÷ 250 = 3,200 mcg/mL

Step 2 - Convert dose/min to dose/hr: 400 mcg/min × 60 = 24,000 mcg/hr

Step 3 - Calculate mL/hr: = 24,000 ÷ 3,200 = 7.5 mL/hr ✅

TYPE 7: Heparin Infusion (Units/hr)

Formula: (Units ordered ÷ Units available) × Volume = mL/hr

Question: A patient is on a Heparin drip at 1,200 units/hr. The bag reads 25,000 units in 500 mL NS. At what rate do you set the pump?

Step 1 - Concentration: 25,000 units ÷ 500 mL = 50 units/mL

Step 2 - mL/hr: = 1,200 ÷ 50 = 24 mL/hr ✅

TYPE 8: Insulin Dosage

Question: A sliding scale orders Regular insulin for a blood glucose of 280 mg/dL: give 8 units subcutaneously. The insulin pen contains U-100 insulin (100 units/mL). How many mL do you draw?

Solution: = 8 units ÷ 100 units/mL

= 0.08 mL ✅

(Note: On an insulin syringe, this reads as 8 units - no conversion needed if using an insulin syringe)

TYPE 9: Reconstitution of Powder

Question: You have a vial of Cefazolin 1 g powder. The instructions say to add 3.4 mL of sterile water to yield a concentration of 225 mg/mL. The order is for 500 mg IV. How many mL do you draw up?

Solution: = (500 mg ÷ 225 mg) × 1 mL

= 2.22 mL ✅

TYPE 10: Percentage Concentration

Formula: % concentration = grams per 100 mL

Question: You have a 500 mL bag of 0.9% Normal Saline. How many grams of sodium chloride does it contain?

Solution: 0.9% = 0.9 g per 100 mL

= 0.9 × (500 ÷ 100)

= 0.9 × 5

= 4.5 g of NaCl ✅

TYPE 11: Pediatric Dose Safety Check (mg/kg range)

Question: A child weighs 15 kg. The doctor orders Ibuprofen 150 mg orally. The safe dose range is 5-10 mg/kg/dose. Is this dose safe?

Solution: Minimum safe dose: 5 × 15 = 75 mg Maximum safe dose: 10 × 15 = 150 mg

Ordered dose: 150 mg - falls within range

= Safe to administer ✅

TYPE 12: Unit Conversion (mcg to mg, etc.)

Question: A patient needs 0.125 mg of Digoxin. Tablets available are 62.5 mcg. How many tablets?

Step 1 - Convert: 0.125 mg = 125 mcg

Step 2 - Calculate: = 125 ÷ 62.5 = 2 tablets ✅

Quick Reference - Key Formulas

Calculation Type	Formula
Tablets/Liquid	(Ordered ÷ On Hand) × Quantity
mg/kg dose	Weight × Dose per kg
IV rate (mL/hr)	Volume ÷ Time (hrs)
Drop rate (gtt/min)	(Volume × Drop factor) ÷ Time (min)
Concentration check	Dose ordered ÷ Concentration
% solution	g per 100 mL

Exam Tip: Always check units before calculating. Convert everything to the same unit (mg, mcg, mL) before applying any formula. When in doubt, use dimensional analysis - it catches unit errors automatically.

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