If an order is 160 mg and the concentration is 160 mg per 5 mL, how many milliliters should be given?

If an order is 160 mg and the concentration is 160 mg per 5 mL, how many milliliters should be given?

• A. 5 mL
• B. 2.5 mL
• C. 10 mL
• D. 1 mL

Answer: (A)

Understanding concentration as mg per mL lets you convert the prescribed amount into a volume. Here, the solution has 160 mg in every 5 mL, so each milliliter contains 160/5 = 32 mg. To deliver 160 mg, you need 160 / 32 = 5 mL. So you should administer 5 mL. If you gave 2.5 mL, you’d deliver 80 mg; 10 mL would deliver 320 mg; 1 mL would deliver 32 mg. The 5 mL amount is correct because it provides the exact 160 mg at this concentration.

Understanding concentration as mg per mL lets you convert the prescribed amount into a volume. Here, the solution has 160 mg in every 5 mL, so each milliliter contains 160/5 = 32 mg. To deliver 160 mg, you need 160 / 32 = 5 mL. So you should administer 5 mL. If you gave 2.5 mL, you’d deliver 80 mg; 10 mL would deliver 320 mg; 1 mL would deliver 32 mg. The 5 mL amount is correct because it provides the exact 160 mg at this concentration.