Following the described dilution, what is the final volume and concentration of phenylephrine produced when 1 mL of 1% phenylephrine is diluted with 9 mL of IV fluid?

• A. 20 mL at 50 mcg/mL
• B. 10 mL at 100 mcg/mL
• C. 10 mL of solution at 100 mcg/mL
• D. 10 mL at 1000 mcg/mL

Answer: (C)

The main idea is that dilution changes concentration but not the total amount of drug. Use the dilution equation C1V1 = C2V2.

Starting with 1% phenylephrine, that’s 10 mg per mL. You take 1 mL, so you have 10 mg of drug. Dilute with 9 mL of IV fluid, giving a final volume of 10 mL. The total amount stays 10 mg, so the final concentration is 10 mg / 10 mL = 1 mg/mL, which is 1000 mcg/mL.

Therefore, the final product is 10 mL at 1000 mcg/mL.