PEBC Pharmaceutical Calculations 5

Question 1

A medication has a half-life of 6 hours. If a patient receives a 500 mg dose, approximately how much drug remains in the body after 24 hours?

Accepted Answer

31.25 mg

Answer

24 hours = 4 half-lives; 500 × (1/2)^4 = 500 ÷ 16 = 31.25 mg.

Question 2

A total parenteral nutrition (TPN) bag contains 500 mL of 50% dextrose and 500 mL of 10% amino acids. What is the final dextrose concentration in the combined 1000 mL solution?

Accepted Answer

25%

Answer

Dextrose content = 500 mL × 0.50 = 250 g; final concentration = 250 g ÷ 1000 mL = 0.25 = 25%.

Question 3

A physician orders vancomycin 15 mg/kg IV every 12 hours for a 70 kg patient. The pharmacy has vancomycin 500 mg/10 mL vials. How many mL are needed per dose?

Accepted Answer

21 mL

Answer

Dose = 15 mg/kg × 70 kg = 1050 mg; concentration = 500 mg/10 mL = 50 mg/mL; volume = 1050 ÷ 50 = 21 mL.

Question 4

An oral solution contains 125 mg of active ingredient per 5 mL. A patient is prescribed 0.375 g twice daily. How many mL should the patient take per dose?

Accepted Answer

15 mL

Answer

0.375 g = 375 mg; volume = (375 mg ÷ 125 mg) × 5 mL = 15 mL per dose.

Question 5

A pharmacy receives an order for potassium chloride 20 mEq IV in 100 mL NS. KCl is available as 2 mEq/mL. How many mL of KCl solution should be added to the bag?

Accepted Answer

10 mL

Answer

Volume = 20 mEq ÷ 2 mEq/mL = 10 mL.

PEBC - Pharmacy Examining Board of Canada Practice Test

PEBC - Pharmacy Examining Board of Canada Practice Test

PEBC Pharmaceutical Calculations 5