A medication is supplied at 1 mg/mL. If the desired dose is 0.25 mg, what volume should be drawn?

• A. 0.25 mL
• B. 0.025 mL
• C. 2.5 mL
• D. 0.5 mL

Answer: (A)

Converting dose to volume using concentration is the key. If the drug is 1 mg per 1 mL, then each milliliter holds 1 mg. To deliver 0.25 mg, you need 0.25 mL because 0.25 mg divided by 1 mg/mL equals 0.25 mL. In general, Volume = Dose ÷ Concentration.

So drawing 0.25 mL provides the desired 0.25 mg. If you drew less or more (for example, 0.025 mL, 0.5 mL, or 2.5 mL), you would administer different amounts of the drug (0.025 mg, 0.5 mg, or 2.5 mg respectively).