A medication is supplied as 50 mg/mL. The dose is 1 mg/kg for a 9 kg child. How many mL should be given?

• A. 0.09 mL
• B. 0.18 mL
• C. 0.27 mL
• D. 0.36 mL

Answer: (B)

Start with converting the weight-based dose to a total milligram dose, then convert the milligrams to milliliters using the concentration. The child is 9 kg and the dose is 1 mg/kg, so total dose = 9 mg. With a concentration of 50 mg per mL, each mL provides 50 mg. To get 9 mg, you need 9 ÷ 50 = 0.18 mL. So the correct administration volume is 0.18 mL. If you used 0.09 mL, you’d give 4.5 mg; 0.27 mL would be 13.5 mg; 0.36 mL would be 18 mg—none match the 9 mg required.