A solution with a concentration of 2 mg/mL is used to deliver a 12 mg dose. How many milliliters are required?

A solution with a concentration of 2 mg/mL is used to deliver a 12 mg dose. How many milliliters are required?

• A. 4 mL
• B. 6 mL
• C. 8 mL
• D. 12 mL

Answer: (B)

Understanding how to convert a dose to a volume is the key here. The relationship is dose = concentration × volume, so to find the volume you divide the dose by the concentration. With a dose of 12 mg and a concentration of 2 mg per mL, the volume needed is 12 mg ÷ (2 mg/mL) = 6 mL. This also checks out by thinking each milliliter delivers 2 mg, and 6 mL × 2 mg/mL equals 12 mg. If you used less than 6 mL, you'd get less than 12 mg (for example, 4 mL would be 8 mg). If you used more, you'd exceed the dose (8 mL would be 16 mg, 12 mL would be 24 mg), so 6 mL is the correct amount.

Understanding how to convert a dose to a volume is the key here. The relationship is dose = concentration × volume, so to find the volume you divide the dose by the concentration. With a dose of 12 mg and a concentration of 2 mg per mL, the volume needed is 12 mg ÷ (2 mg/mL) = 6 mL. This also checks out by thinking each milliliter delivers 2 mg, and 6 mL × 2 mg/mL equals 12 mg. If you used less than 6 mL, you'd get less than 12 mg (for example, 4 mL would be 8 mg). If you used more, you'd exceed the dose (8 mL would be 16 mg, 12 mL would be 24 mg), so 6 mL is the correct amount.