A child weighing 13 kg has an order for vancomycin 50 mg/kg/day divided into three doses. The vial contains 500 mg in 100 mL of 0.9% saline. How many milliliters should be administered per dose?

• A. 14 mL
• B. 43 mL
• C. 86 mL
• D. 215 mL

Answer: (B)

Calculating the dose from weight and converting to a volume using the vial’s concentration.

First, total daily dose: 13 kg × 50 mg/kg/day = 650 mg per day. Since it’s given in three divided doses, each dose is 650 ÷ 3 ≈ 216.7 mg.

The vial concentration is 500 mg in 100 mL, which is 5 mg/mL. To deliver 216.7 mg, the required volume is 216.7 mg ÷ 5 mg/mL ≈ 43.3 mL per dose. Rounding to the nearest whole mL gives about 43 mL per dose.

Thus, the per-dose administration is approximately 43 mL. The other volumes would deliver far more or far less medication (for example, 14 mL = ~70 mg per dose; 86 mL = ~430 mg per dose), which doesn’t match the calculated per-dose requirement.