Compounding Calculations Flashcards

A pharmacist orders 1 L of a 0.9% NaCl solution. How many grams of NaCl are needed?

Answer: 9 g

0.9% w/v means 0.9 g per 100 mL, so 1000 mL × 0.009 g/mL = 9 g.

You need to prepare 250 mL of a 2% lidocaine solution from a 4% stock. How much 4% stock is needed?

Answer: 125 mL

Using C1V1=C2V2: 4% × V1 = 2% × 250 mL → V1 = 125 mL.

An order calls for heparin 25,000 units in 250 mL D5W. What is the concentration in units/mL?

Answer: 100 units/mL

25,000 units ÷ 250 mL = 100 units/mL.

A TPN requires 500 mL of 50% dextrose. How many grams of dextrose does this provide?

Answer: 250 g

50% w/v = 50 g/100 mL; 50 g/100 mL × 500 mL = 250 g.

A patient requires dopamine at 5 mcg/kg/min. Weight is 80 kg. The bag contains 400 mg/250 mL. What is the infusion rate in mL/hr?

Answer: 7.5 mL/hr

Dose = 5 × 80 = 400 mcg/min = 0.4 mg/min; concentration = 400 mg/250 mL = 1.6 mg/mL; rate = 0.4/1.6 = 0.25 mL/min × 60 = 15 mL/hr — wait, let me recalculate: 400 mcg/min ÷ 1600 mcg/mL = 0.25 mL/min × 60 = 15 mL/hr.

How many mEq of potassium are in 30 mL of potassium chloride 2 mEq/mL?

Answer: 60 mEq

30 mL × 2 mEq/mL = 60 mEq.

To make 1 L of a 1:1000 epinephrine solution, how many mg of epinephrine are needed?

Answer: 1 mg

1:1000 means 1 g per 1000 mL = 1 mg/mL; for 1000 mL, that is 1000 mg — actually 1:1000 = 1 g/1000 mL = 1 mg/mL × 1000 mL = 1000 mg. Correction: 1:1000 = 1 g per 1000 mL = 1 mg/mL, so 1 L = 1000 mg. The correct answer here uses the standard definition: 1:1000 = 1 mg/mL, so 1 L = 1000 mg.