NAPLEX QBANK Pharmaceutical Calculations Questions and Answers — Questions and Answers
Question 1: A patient is to receive an IV infusion of 0.9% NaCl with 20 mEq of KCl over 8 hours. The total volume of the IV bag is 1000 mL. The IV administration set delivers 15 gtt/mL. What is the correct flow rate in drops per minute (gtt/min)?
- 21 gtt/min
- 15 gtt/min
- 31 gtt/min (Correct answer)
- 125 gtt/min
Correct answer: 31 gtt/min
First, calculate the flow rate in mL/hr: 1000 mL / 8 hours = 125 mL/hr. Next, convert mL/hr to mL/min: 125 mL / 60 min = 2.083 mL/min. Finally, use the administration set's drop factor to find the rate in gtt/min: 2.083 mL/min * 15 gtt/mL = 31.25 gtt/min. Rounding to the nearest whole number gives 31 gtt/min.
Question 2: A pharmacist needs to prepare 120 g of a 2.5% hydrocortisone cream by mixing 1% and 5% hydrocortisone creams. How many grams of the 5% cream are required?
- 45 g (Correct answer)
- 75 g
- 60 g
- 30 g
Correct answer: 45 g
This is an alligation problem. Set up the alligation grid. The desired percentage (2.5%) is in the center. The higher (5%) and lower (1%) concentrations are on the left. Subtract diagonally: 2.5 - 1 = 1.5 (parts of 5% cream) and 5 - 2.5 = 2.5 (parts of 1% cream). The total parts are 1.5 + 2.5 = 4 parts. The proportion of the 5% cream needed is 1.5/4. Calculate the amount needed: (1.5 / 4) * 120 g = 45 g.
Question 3: A prescription for a pediatric patient weighing 44 lbs is for amoxicillin 30 mg/kg/day, divided into two daily doses. The pharmacy has amoxicillin oral suspension with a concentration of 250 mg/5 mL. How many mL should be dispensed for each dose?
- 12 mL
- 6 mL (Correct answer)
- 15 mL
- 7.5 mL
Correct answer: 6 mL
First, convert the patient's weight from pounds to kilograms: 44 lbs / 2.2 lbs/kg = 20 kg. Next, calculate the total daily dose in mg: 20 kg * 30 mg/kg/day = 600 mg/day. Since the dose is divided into two daily doses, each dose is 600 mg / 2 = 300 mg. Finally, calculate the volume in mL for each dose using the suspension's concentration: (300 mg / 250 mg) * 5 mL = 6 mL.
Question 4: Which of the following represents the correct calculation for the osmolarity (mOsmol/L) of a 3% hypertonic saline (NaCl) solution? (MW of Na = 23, MW of Cl = 35.5)
- (30 g/L / 58.5 g/mol) * 1 * 1000
- (3 g/L / 58.5 g/mol) * 2 * 1000
- (30 g/L / 58.5 g/mol) * 2 * 1000 (Correct answer)
- (30 g/L / 94.5 g/mol) * 2 * 1000
Correct answer: (30 g/L / 58.5 g/mol) * 2 * 1000
Osmolarity (mOsmol/L) = (Concentration in g/L / MW in g/mol) * number of species * 1000. A 3% solution is 3 g/100 mL, which is 30 g/L. The molecular weight (MW) of NaCl is 23 + 35.5 = 58.5 g/mol. NaCl dissociates into 2 species (Na+ and Cl-). Therefore, the correct calculation is (30 g/L / 58.5 g/mol) * 2 * 1000.
Question 5: A patient's creatinine clearance is calculated to be 45 mL/min. The standard dose of Drug X is 500 mg every 12 hours for patients with a CrCl > 60 mL/min. The dosing guidelines recommend a 50% dose reduction for patients with a CrCl between 30-60 mL/min. What is the appropriate adjusted daily dose for this patient?
- 500 mg (Correct answer)
- 1000 mg
- 250 mg
- 750 mg
Correct answer: 500 mg
The standard total daily dose is 500 mg/dose * 2 doses/day = 1000 mg/day. The patient's CrCl of 45 mL/min falls into the 30-60 mL/min range, which requires a 50% dose reduction. The adjusted daily dose is 1000 mg * 0.50 = 500 mg/day.
Question 6: You are asked to compound 240 mL of a 1:500 (w/v) solution. The drug is available as a pure powder. How many milligrams of the drug powder are needed?
- 120 mg
- 240 mg
- 480 mg (Correct answer)
- 500 mg
Correct answer: 480 mg
A 1:500 w/v solution means there is 1 gram of solute in every 500 mL of solution. To find out how much drug is needed for 240 mL, a proportion can be set up: (1 g / 500 mL) = (x g / 240 mL). Solving for x gives: x = (1 * 240) / 500 = 0.48 g. To convert grams to milligrams, multiply by 1000: 0.48 g * 1000 mg/g = 480 mg.
NAPLEX QBANK Pharmaceutical Calculations Questions and Answers
A patient is to receive an IV infusion of 0.9% NaCl with 20 mEq of KCl over 8 hours.
The total volume of the IV bag is 1000 mL.
The IV administration set delivers 15 gtt/mL.
What is the correct flow rate in drops per minute (gtt/min)?