A vial contains 1.5 mg/mL; you need to deliver 6 mg. How many milliliters should be drawn?

A vial contains 1.5 mg/mL; you need to deliver 6 mg. How many milliliters should be drawn?

• A. 2 mL
• B. 3 mL
• C. 4 mL
• D. 6 mL

Answer: (C)

When you have a drug concentration, you convert the prescribed dose into the volume to draw using Volume = Dose ÷ Concentration. Here, the vial provides 1.5 mg for every 1 mL. To get 6 mg, divide 6 by 1.5, which equals 4. So drawing 4 mL delivers 6 mg (4 × 1.5 mg). Drawing less would give less than 6 mg, and drawing more would give more than 6 mg, so 4 mL is the exact amount.

When you have a drug concentration, you convert the prescribed dose into the volume to draw using Volume = Dose ÷ Concentration. Here, the vial provides 1.5 mg for every 1 mL. To get 6 mg, divide 6 by 1.5, which equals 4. So drawing 4 mL delivers 6 mg (4 × 1.5 mg). Drawing less would give less than 6 mg, and drawing more would give more than 6 mg, so 4 mL is the exact amount.