A physician prescribes 400,000 units of penicillin G benzathine. The medication label shows 300,000 units per 10 mL. How many milliliters should the nurse administer? Round to the nearest whole number.

A physician prescribes 400,000 units of penicillin G benzathine. The medication label shows 300,000 units per 10 mL. How many milliliters should the nurse administer? Round to the nearest whole number.

• A. 10 mL
• B. 13 mL
• C. 15 mL
• D. 20 mL

Answer: (B)

Start with the concentration: 300,000 units in 10 mL means 30,000 units per 1 mL. To deliver 400,000 units, divide the prescribed amount by the units per mL: 400,000 ÷ 30,000 = 13.333 mL. Rounding to the nearest whole number gives 13 mL. Therefore, 13 mL should be administered. (Note: this is a relatively large injection volume and may require consideration of injection sites or dividing the dose in practice.)

Start with the concentration: 300,000 units in 10 mL means 30,000 units per 1 mL. To deliver 400,000 units, divide the prescribed amount by the units per mL: 400,000 ÷ 30,000 = 13.333 mL. Rounding to the nearest whole number gives 13 mL. Therefore, 13 mL should be administered. (Note: this is a relatively large injection volume and may require consideration of injection sites or dividing the dose in practice.)