CAOP Pharmaceutical Calculations 5

Question 1

A drug has a Vd of 0.5 L/kg and F = 1. What loading dose achieves a plasma concentration of 15 mg/L in a 70-kg patient?

Accepted Answer

525 mg

Answer

LD = Vd × Cp ÷ F = (0.5 × 70) L × 15 mg/L = 525 mg.

Question 2

A drug has an elimination rate constant of 0.1155 h⁻¹. What is its half-life?

Accepted Answer

6 hours

Answer

t½ = 0.693 ÷ k = 0.693 ÷ 0.1155 = 6 hours.

Question 3

Assuming first-order elimination, what percentage of a drug remains after 4 half-lives?

Accepted Answer

6.25%

Answer

(1/2)⁴ = 1/16 = 6.25% remaining.

Question 4

A solution contains 0.0005% w/v of an impurity. What is that in parts per million?

Accepted Answer

5 ppm

Answer

1% = 10,000 ppm, so 0.0005% × 10,000 = 5 ppm.

Question 5

250 mg of a drug is dissolved in enough water to make 50 mL. What is the % w/v concentration?

Accepted Answer

0.5%

Answer

0.25 g ÷ 50 mL × 100 = 0.5% w/v.

CAOP - Competency Assessment of Overseas Pharmacist Practice Test