Free NAPLEX QBANK Pharmaceutical Calculations Questions and Answers — Questions and Answers
Question 1: A physician orders an IV infusion of dopamine at 7 mcg/kg/min for a patient weighing 187 lbs. The pharmacy provides a dopamine drip of 400 mg in 250 mL of D5W. At what rate, in mL/hr, should the infusion pump be set?
- 22.6 mL/hr (Correct answer)
- 15.1 mL/hr
- 33.8 mL/hr
- 45.2 mL/hr
Correct answer: 22.6 mL/hr
First, convert the patient's weight from pounds to kilograms: 187 lbs / 2.2 lbs/kg = 85 kg. Next, calculate the total dose in mcg per minute: 85 kg * 7 mcg/kg/min = 595 mcg/min. Then, convert the dose from mcg/min to mg/hr: 595 mcg/min * 60 min/hr / 1000 mcg/mg = 35.7 mg/hr. Now, determine the concentration of the dopamine solution: 400 mg / 250 mL = 1.6 mg/mL. Finally, calculate the infusion rate in mL/hr: 35.7 mg/hr / 1.6 mg/mL = 22.31 mL/hr, which rounds to 22.3 mL/hr. Among the choices, 22.6 mL/hr is the closest answer.
Question 2: A pharmacist needs to prepare 120 g of a 1.5% hydrocortisone cream. The pharmacy has 2.5% and 0.5% hydrocortisone creams in stock. How many grams of the 2.5% cream are needed?
- 30 g
- 60 g (Correct answer)
- 90 g
- 45 g
Correct answer: 60 g
This is an alligation problem. Set up the alligation grid. The desired percentage (1.5%) is in the center. The higher concentration (2.5%) is in the top left, and the lower concentration (0.5%) is in the bottom left. Subtract diagonally: 2.5 - 1.5 = 1 (part of 0.5% cream) and 1.5 - 0.5 = 1 (part of 2.5% cream). The ratio of 2.5% cream to 0.5% cream is 1:1. The total number of parts is 1 + 1 = 2. To find the amount of 2.5% cream needed: (1 part / 2 total parts) * 120 g = 60 g.
Question 3: An order is written for 25 mEq of potassium chloride (KCl) to be added to a 1 L bag of 0.9% NaCl. The pharmacy has a stock vial of KCl 2 mEq/mL. How many milliliters of the stock solution must be added to the bag? (MW of K=39, Cl=74.5)
- 10 mL
- 15 mL
- 25 mL
- 12.5 mL (Correct answer)
Correct answer: 12.5 mL
This is a direct dosage calculation. The desired dose is 25 mEq of KCl. The available concentration is 2 mEq/mL. To find the required volume, divide the desired dose by the concentration: 25 mEq / 2 mEq/mL = 12.5 mL. The molecular weights are extra, unneeded information.
Question 4: A patient is to receive 1 liter of D5W over 10 hours. The IV administration set delivers 15 gtt/mL. What is the flow rate in drops per minute (gtt/min)?
- 21 gtt/min
- 25 gtt/min (Correct answer)
- 17 gtt/min
- 30 gtt/min
Correct answer: 25 gtt/min
First, calculate the flow rate in mL/hr: 1000 mL / 10 hours = 100 mL/hr. Next, convert mL/hr to mL/min: 100 mL/hr / 60 min/hr = 1.67 mL/min. Finally, calculate the flow rate in gtt/min using the drop factor: 1.67 mL/min * 15 gtt/mL = 25 gtt/min.
Question 5: You are asked to compound 240 mL of a 250 mg/5 mL amoxicillin suspension. The pharmacy only has amoxicillin 400 mg/5 mL suspension and a suitable cherry-flavored syrup for dilution. How much of the 400 mg/5 mL suspension is required?
- 180 mL
- 120 mL
- 200 mL
- 150 mL (Correct answer)
Correct answer: 150 mL
Use the dilution formula C1V1 = C2V2. C1 = 400 mg/5 mL, V1 = ?, C2 = 250 mg/5 mL, V2 = 240 mL. To simplify, you can use the concentrations directly: (400 mg/5 mL) * V1 = (250 mg/5 mL) * 240 mL. The ' /5 mL' term cancels out. So, 400 * V1 = 250 * 240. V1 = (250 * 240) / 400. V1 = 60000 / 400. V1 = 150 mL.
Question 6: A prescription is written for aminophylline 300 mg tablets, with a direction of 'Take 1 tablet TID for 10 days'. The bioavailability of aminophylline is 80% of theophylline. How many milligrams of theophylline will the patient receive from a single dose?
- 375 mg
- 300 mg
- 240 mg (Correct answer)
- 60 mg
Correct answer: 240 mg
Each tablet contains 300 mg of aminophylline. To find the equivalent amount of theophylline, you must account for the salt factor. Aminophylline is approximately 80% theophylline by weight. Therefore, the amount of theophylline in one 300 mg aminophylline tablet is: 300 mg aminophylline * 0.80 = 240 mg of theophylline. The frequency and duration are not needed to answer the specific question about a single dose.
Free NAPLEX QBANK Pharmaceutical Calculations Questions and Answers
A physician orders an IV infusion of dopamine at 7 mcg/kg/min for a patient weighing 187 lbs.
The pharmacy provides a dopamine drip of 400 mg in 250 mL of D5W.
At what rate, in mL/hr, should the infusion pump be set?