A 25 mg dose is prescribed. The suspension concentration is 25 mg per 5 mL. What volume in mL is needed?

A 25 mg dose is prescribed. The suspension concentration is 25 mg per 5 mL. What volume in mL is needed?

• A. 1 mL
• B. 3 mL
• C. 5 mL
• D. 7 mL

Answer: (C)

The key idea is to use the suspension’s concentration to convert the desired dose into a volume. The suspension has 25 mg in 5 mL, which is 25 mg ÷ 5 mL = 5 mg per mL. To deliver 25 mg, you need a volume that contains 25 mg at 5 mg per mL, so 25 mg ÷ 5 mg/mL = 5 mL. Therefore, 5 mL is needed. If you used 1 mL, you’d administer 5 mg; 3 mL would give 15 mg; 7 mL would give 35 mg, none of which match the 25 mg dose.

The key idea is to use the suspension’s concentration to convert the desired dose into a volume. The suspension has 25 mg in 5 mL, which is 25 mg ÷ 5 mL = 5 mg per mL. To deliver 25 mg, you need a volume that contains 25 mg at 5 mg per mL, so 25 mg ÷ 5 mg/mL = 5 mL. Therefore, 5 mL is needed. If you used 1 mL, you’d administer 5 mg; 3 mL would give 15 mg; 7 mL would give 35 mg, none of which match the 25 mg dose.