A vial contains 100 mg in 4 mL. If the prescribed dose is 25 mg, how many mL should be drawn?

A vial contains 100 mg in 4 mL. If the prescribed dose is 25 mg, how many mL should be drawn?

• A. 1 mL
• B. 0.5 mL
• C. 2 mL
• D. 4 mL

Answer: (B)

This tests converting a prescribed dose to the volume using the vial’s concentration. The vial has 100 mg in 4 mL, so the concentration is 25 mg per mL. To obtain a 25 mg dose, draw volume = 25 mg ÷ 25 mg/mL = 1 mL. So the correct drawn volume is 1 milliliter. A smaller volume (0.5 mL) would yield 12.5 mg, a larger volume (2 mL) would yield 50 mg, and 4 mL would yield 100 mg, none matching the prescribed dose.

This tests converting a prescribed dose to the volume using the vial’s concentration. The vial has 100 mg in 4 mL, so the concentration is 25 mg per mL. To obtain a 25 mg dose, draw volume = 25 mg ÷ 25 mg/mL = 1 mL. So the correct drawn volume is 1 milliliter. A smaller volume (0.5 mL) would yield 12.5 mg, a larger volume (2 mL) would yield 50 mg, and 4 mL would yield 100 mg, none matching the prescribed dose.