A clinician orders methylprednisolone at 1.5 mg/kg for a child weighing 75 pounds. The available vial is 125 mg in 2 mL. What volume (in mL) should be administered?

A clinician orders methylprednisolone at 1.5 mg/kg for a child weighing 75 pounds. The available vial is 125 mg in 2 mL. What volume (in mL) should be administered?

• A. 0.41 ml
• B. 0.82 ml
• C. 1.64 ml
• D. 1.23 ml

Answer: (B)

Start with converting weight to kilograms, then apply the mg/kg dose, and finally convert the required milligrams to milliliters using the vial’s concentration. 75 lb ÷ 2.2 ≈ 34.1 kg. At 1.5 mg/kg, the total dose needed is 34.1 × 1.5 ≈ 51 mg. The vial provides 125 mg in 2 mL, which is 62.5 mg per mL. To find the volume: 51 mg ÷ 62.5 mg/mL ≈ 0.818 mL, which rounds to 0.82 mL. So the correct volume to administer is about 0.82 mL. Why the other numbers don’t fit: 0.41 mL would deliver roughly 25.6 mg, half the required dose; 1.23 mL would deliver about 76.9 mg, well above the needed 51 mg; 1.64 mL would deliver about 102.5 mg, also too high.

Start with converting weight to kilograms, then apply the mg/kg dose, and finally convert the required milligrams to milliliters using the vial’s concentration.

75 lb ÷ 2.2 ≈ 34.1 kg. At 1.5 mg/kg, the total dose needed is 34.1 × 1.5 ≈ 51 mg. The vial provides 125 mg in 2 mL, which is 62.5 mg per mL. To find the volume: 51 mg ÷ 62.5 mg/mL ≈ 0.818 mL, which rounds to 0.82 mL. So the correct volume to administer is about 0.82 mL.

Why the other numbers don’t fit: 0.41 mL would deliver roughly 25.6 mg, half the required dose; 1.23 mL would deliver about 76.9 mg, well above the needed 51 mg; 1.64 mL would deliver about 102.5 mg, also too high.