Pharmacy Dosage Calculations 3 — Questions and Answers
Question 1: A patient weighs 88 kg and is prescribed 5 mg/kg/day of a medication divided into two doses. What is each dose in mg?
- 110 mg
- 176 mg
- 220 mg (Correct answer)
- 440 mg
Correct answer: 220 mg
Daily dose: 88 kg × 5 mg/kg = 440 mg/day. Each dose: 440 ÷ 2 = 220 mg.
Question 2: How many grams of dextrose are in 500 mL of D5W (5% dextrose in water)?
- 5 g
- 10 g
- 25 g (Correct answer)
- 50 g
Correct answer: 25 g
5% means 5 g per 100 mL. In 500 mL: 5 g/100 mL × 500 mL = 25 g.
Question 3: A prescription reads: metformin 1,000 mg PO BID × 30 days. How many tablets of 500 mg strength are needed to fill this prescription?
- 60 tablets
- 90 tablets
- 120 tablets (Correct answer)
- 180 tablets
Correct answer: 120 tablets
1,000 mg ÷ 500 mg/tab = 2 tabs per dose. BID = 2 doses/day. 2 × 2 × 30 = 120 tablets.
Question 4: An ointment requires 3% salicylic acid. The pharmacy has 6% and 1% preparations. Using alligation, what ratio of 6% to 1% is needed?
- 1:1
- 2:3 (Correct answer)
- 2:1
- 3:2
Correct answer: 2:3
Alligation: higher (6%) – desired (3%) = 3 parts of lower; desired (3%) – lower (1%) = 2 parts of higher. Ratio 6%:1% = 2:3.
Question 5: Convert 2.5 tablespoons to mL. (1 tablespoon = 15 mL)
- 25 mL
- 30 mL
- 37.5 mL (Correct answer)
- 45 mL
Correct answer: 37.5 mL
2.5 tbsp × 15 mL/tbsp = 37.5 mL.
Question 6: A solution contains 250 mcg/mL. A patient needs 0.5 mg. How many mL should be administered?
- 0.5 mL
- 1 mL
- 2 mL (Correct answer)
- 5 mL
Correct answer: 2 mL
0.5 mg = 500 mcg. 500 mcg ÷ 250 mcg/mL = 2 mL.
Pharmacy Dosage Calculations 3
A patient weighs 88 kg and is prescribed 5 mg/kg/day of a medication divided into two doses.
What is each dose in mg?