A patient needs 125 mg. The suspension concentration is 250 mg per 5 mL. What volume in mL should be given?

A patient needs 125 mg. The suspension concentration is 250 mg per 5 mL. What volume in mL should be given?

• A. 2.5 mL
• B. 5 mL
• C. 1 mL
• D. 0.5 mL

Answer: (A)

To dose from a suspension, convert the labeled strength to mg per mL, then use that to find the required volume. The suspension has 250 mg in 5 mL, which equals 250 ÷ 5 = 50 mg per mL. To deliver 125 mg, you need 125 ÷ 50 = 2.5 mL. You can also see this with a proportion: 125 mg / x mL = 250 mg / 5 mL; cross-multiplying gives x = (125 × 5) / 250 = 2.5 mL. Sanity check: 125 mg is half of 250 mg, so you use half of 5 mL, which is 2.5 mL.

To dose from a suspension, convert the labeled strength to mg per mL, then use that to find the required volume. The suspension has 250 mg in 5 mL, which equals 250 ÷ 5 = 50 mg per mL. To deliver 125 mg, you need 125 ÷ 50 = 2.5 mL. You can also see this with a proportion: 125 mg / x mL = 250 mg / 5 mL; cross-multiplying gives x = (125 × 5) / 250 = 2.5 mL. Sanity check: 125 mg is half of 250 mg, so you use half of 5 mL, which is 2.5 mL.