CPhT Dosage Calculations 4

Question 1

A pharmacist prepares 120 mL of a 5% dextrose solution using a 50% dextrose stock. How many mL of the 50% stock are needed?

Accepted Answer

12 mL

Answer

Using C1V1 = C2V2: 50% × V1 = 5% × 120 mL; V1 = 600 ÷ 50 = 12 mL.

Question 2

A pediatric patient requires 1.5 mL/kg/hr of IV fluid. The patient weighs 16 kg. How many mL will the patient receive over 8 hours?

Accepted Answer

192 mL

Answer

1.5 mL/kg/hr × 16 kg = 24 mL/hr × 8 hr = 192 mL.

Question 3

A drug order calls for 0.3 mg of a drug. The stock solution contains 1 mg per 2 mL. What volume should be drawn up?

Accepted Answer

0.6 mL

Answer

1 mg per 2 mL = 0.5 mg/mL; 0.3 mg ÷ 0.5 mg/mL = 0.6 mL.

Question 4

An infusion should deliver 750 mL over 6 hours using a 15 gtt/mL set. What is the drip rate in gtt/min?

Accepted Answer

21 gtt/min

Answer

750 mL ÷ 6 hr = 125 mL/hr ÷ 60 min × 15 gtt/mL = 31.25 ≈ 31 gtt/min.

Question 5

A compound requires 1:500 dilution of epinephrine. If the final volume is 1,000 mL, how many mL of concentrate are needed?

Accepted Answer

2 mL

Answer

1:500 means 1 mL per 500 mL; 1,000 mL ÷ 500 = 2 mL of concentrate.

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