APC Pharmaceutical Calculations 3

Question 1

Using the alligation method, what volume of 70% alcohol is needed to prepare 500 mL of 50% alcohol using 70% and 30% alcohol?

Accepted Answer

250 mL

Answer

Alligation gives equal parts (20:20), so each concentration contributes 250 mL to make 500 mL total.

Question 2

A morphine infusion is prepared as 50 mg in 50 mL of normal saline running at 3 mL/hour. How many mg/hour is the patient receiving?

Accepted Answer

3 mg/hr

Answer

Concentration = 50 mg ÷ 50 mL = 1 mg/mL; dose rate = 1 mg/mL × 3 mL/hr = 3 mg/hr.

Question 3

A patient's creatinine clearance is 30 mL/min. Normal gentamicin dosing is every 24 hours (based on normal CrCl of 120 mL/min). If the interval is extended proportionally, what is the new interval?

Accepted Answer

96 hours

Answer

New interval = 24 hr × (120 ÷ 30) = 24 × 4 = 96 hours.

Question 4

A prescription requires a 1:200 w/v solution. How many milligrams of solute are contained in 400 mL of this solution?

Accepted Answer

2000 mg

Answer

1:200 w/v = 1 g per 200 mL; in 400 mL: (400 ÷ 200) × 1 g = 2 g = 2000 mg.

Question 5

A powder for injection contains 1.5 g. After reconstitution, the final volume is 60 mL. What is the final concentration in mg/mL?

Accepted Answer

25 mg/mL

Answer

Concentration = 1500 mg ÷ 60 mL = 25 mg/mL.

(APC) Australian Pharmacy Council Practice Test

(APC) Australian Pharmacy Council Practice Test

APC Pharmaceutical Calculations 3