PEBC Pharmaceutical Calculations 3

Question 1

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)

Accepted Answer

250 g, 850 kcal

Answer

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

Question 2

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?

Accepted Answer

20 mL

Answer

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

Question 3

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⁻)

Accepted Answer

308 mOsm/L

Answer

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

Question 4

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?

Accepted Answer

300 mL at 200 mL/hr

Answer

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

Question 5

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?

Accepted Answer

200 mg

Answer

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

PEBC - Pharmacy Examining Board of Canada Practice Test