In a pediatric patient, calculate the per-dose volume for a methylprednisolone dose of 0.5 mg/kg/day for a 25 kg child, given in two divided doses daily, with a 20 mg/mL vial. What is the per-dose volume rounded to the nearest tenth of a milliliter?

• A. 0.2 mL
• B. 0.3 mL
• C. 0.4 mL
• D. 0.5 mL

Answer: (B)

Understanding how to convert a mg/kg dose to a mL dose using the vial’s concentration is the key. Start by finding the total daily dose: 0.5 mg per kg per day times 25 kg gives 12.5 mg daily. Since the dose is split into two administrations, each dose is 12.5 mg ÷ 2 = 6.25 mg per dose. With a concentration of 20 mg/mL, the volume for each 6.25 mg dose is 6.25 mg ÷ 20 mg/mL = 0.3125 mL. Rounding to the nearest tenth gives 0.3 mL per dose. So the per-dose volume is 0.3 mL.