A medication label lists 250 mg per 5 mL. If ordered 500 mg, how many milliliters are required?

A medication label lists 250 mg per 5 mL. If ordered 500 mg, how many milliliters are required?

• A. 5 mL
• B. 10 mL
• C. 15 mL
• D. 20 mL

Answer: (B)

The key idea is that dose and volume are proportional for a fixed concentration. The label shows 250 mg in 5 mL, which is a concentration of 50 mg per mL. To reach 500 mg, you need twice as much medication, so you need twice the volume: 2 × 5 mL = 10 mL. Calculated another way, 500 mg × (5 mL / 250 mg) = 10 mL, with the milligram units canceling out. So the required volume is 10 mL. If you used 5 mL, you’d get 250 mg; 15 mL would give 750 mg; 20 mL would give 1000 mg.

The key idea is that dose and volume are proportional for a fixed concentration. The label shows 250 mg in 5 mL, which is a concentration of 50 mg per mL. To reach 500 mg, you need twice as much medication, so you need twice the volume: 2 × 5 mL = 10 mL. Calculated another way, 500 mg × (5 mL / 250 mg) = 10 mL, with the milligram units canceling out. So the required volume is 10 mL. If you used 5 mL, you’d get 250 mg; 15 mL would give 750 mg; 20 mL would give 1000 mg.