Pharmaceutical Calculations Flashcards

A TPN bag contains 500 mL of 50% dextrose. How many grams of dextrose and how many kilocalories does this provide? (1 g dextrose = 3.4 kcal)

Answer: 250 g, 850 kcal

50% × 500 mL = 250 g dextrose; 250 g × 3.4 kcal/g = 850 kcal.

A physician orders 40 mEq of KCl IV over 4 hours. KCl is available as 2 mEq/mL. How many mL of KCl should be added to the IV bag?

Answer: 20 mL

40 mEq ÷ 2 mEq/mL = 20 mL of KCl solution.

What is the osmolarity of a 0.9% NaCl (normal saline) solution? (NaCl MW = 58.5 g/mol; assume complete dissociation into Na⁺ and Cl⁻)

Answer: 308 mOsm/L

9 g/L ÷ 58.5 g/mol = 0.1538 mol/L × 2 ions × 1000 = 308 mOsm/L.

Vancomycin 1500 mg is to be infused over 1.5 hours using a concentration of 5 mg/mL. What volume and rate should be set?

Answer: 300 mL at 200 mL/hr

Volume = 1500 mg ÷ 5 mg/mL = 300 mL; Rate = 300 mL ÷ 1.5 hr = 200 mL/hr.

Using Young's rule [Child dose = Age/(Age + 12) × Adult dose], what is the dose for an 8-year-old child when the adult dose is 500 mg?

Answer: 200 mg

8 ÷ (8 + 12) × 500 = 8/20 × 500 = 0.4 × 500 = 200 mg.

Which ratio strength is equivalent to a 0.02% (w/v) solution?

Answer: 1:5000

0.02% = 0.02 g per 100 mL = 1 g per 5000 mL = 1:5000.

A drug has an elimination half-life of 6 hours. If a patient receives a 400 mg dose, how much drug remains after 18 hours?

Answer: 50 mg

18 hours ÷ 6 hours/half-life = 3 half-lives; 400 → 200 → 100 → 50 mg.