Sterile Compounding Calculations 1 Flashcards

A 500 mL bag of 0.9% sodium chloride is ordered to infuse over 4 hours using a 15 gtt/mL administration set. What is the required flow rate in drops per minute?

Answer: 31 gtt/min

Flow rate (gtt/min) = (Volume × drop factor) ÷ time in minutes = (500 mL × 15 gtt/mL) ÷ (4 hr × 60 min/hr) = 7,500 ÷ 240 = 31.25, rounded to 31 gtt/min.

A ceftriaxone 1 g powder vial is reconstituted with 9.6 mL of sterile water for injection, yielding a total volume of 10 mL. What is the resulting concentration?

Answer: 100 mg/mL

Concentration = amount of drug ÷ final volume = 1,000 mg ÷ 10 mL = 100 mg/mL. Always use the final reconstituted volume, not the diluent volume added.

A patient is ordered a heparin infusion at 1,200 units/hr. The bag is prepared as 25,000 units of heparin in 500 mL D5W. At what rate should the infusion pump be set?

Answer: 24 mL/hr

First find the concentration: 25,000 units ÷ 500 mL = 50 units/mL. Then rate = dose ÷ concentration = 1,200 units/hr ÷ 50 units/mL = 24 mL/hr.

How many mL of a 70% dextrose solution must be mixed with sterile water for injection to prepare 500 mL of a 10% dextrose solution?

Answer: 71.4 mL

Using alligation: parts of 70% = (10 − 0) = 10 parts; parts of water = (70 − 10) = 60 parts; total = 70 parts. Volume of 70% solution = (10 ÷ 70) × 500 mL = 71.4 mL.

A 60-kg patient requires gentamicin 2 mg/kg IV every 8 hours. The available vial is labeled 40 mg/mL. How many mL should be drawn up for each dose?

Answer: 3.0 mL

Step 1 — calculate the dose: 2 mg/kg × 60 kg = 120 mg. Step 2 — calculate the volume: 120 mg ÷ 40 mg/mL = 3 mL per dose.

A TPN order calls for a continuous infusion at 80 mL/hr for 24 hours. How many 1,000 mL bags will the pharmacy need to prepare?

Answer: 2 bags

Total volume needed = 80 mL/hr × 24 hr = 1,920 mL. Dividing by 1,000 mL per bag = 1.92 bags, which must be rounded up to 2 bags to cover the full 24-hour infusion.