A dose of 0.25 g is prescribed. The stock solution provides 125 mg per 5 mL. How many milliliters should be administered?

A dose of 0.25 g is prescribed. The stock solution provides 125 mg per 5 mL. How many milliliters should be administered?

• A. 5 mL
• B. 2 mL
• C. 10 mL
• D. 20 mL

Answer: (C)

To dose using a stock solution, convert the prescribed amount to the same units as the solution’s concentration and then divide by the concentration per milliliter. The order is 0.25 g, which is 250 mg. The stock provides 125 mg in 5 mL, which is 25 mg per mL. So how many milliliters deliver 250 mg? 250 mg ÷ 25 mg/mL = 10 mL. Cross-check: if you set up 125 mg/5 mL = 250 mg/X mL, then X = (5 × 250) / 125 = 10 mL. Five milliliters would give only 125 mg, and twenty milliliters would give 500 mg, so ten milliliters is the correct amount to administer.

To dose using a stock solution, convert the prescribed amount to the same units as the solution’s concentration and then divide by the concentration per milliliter.

The order is 0.25 g, which is 250 mg. The stock provides 125 mg in 5 mL, which is 25 mg per mL. So how many milliliters deliver 250 mg? 250 mg ÷ 25 mg/mL = 10 mL.

Cross-check: if you set up 125 mg/5 mL = 250 mg/X mL, then X = (5 × 250) / 125 = 10 mL.

Five milliliters would give only 125 mg, and twenty milliliters would give 500 mg, so ten milliliters is the correct amount to administer.