A nurse is preparing to administer cephalexin 50 mg/kg/day PO divided in equal doses every 6 hr to a preschooler who weighs 37 lb. Available is cephalexin suspension 250 mg/5 mL. How many mL should the nurse administer per dose? (Round the answer to the nearest tenth. Use a leading zero if it applies. Do not use a trailing zero.)

Calculation: Convert the preschooler's weight from pounds (lb) to kilograms (kg) using the conversion factor of 2.2 lb/kg. Patient's weight in kg = 37 lb / 2.2 lb/kg = 16.8181 kg. Calculate the total daily dose in milligrams (mg) for the child. Total daily dose = Ordered dose (mg/kg/day) × Patient's weight (kg) = 50 mg/kg/day × 16.8181 kg = 840.905 mg/day. Calculate the dose per administration (every 6 hr, which is 4 doses per day). Dose per administration = Total daily dose (mg/day) / 4 doses/day = 840.905 mg / 4 = 210.226 mg/dose. Determine the concentration of the available medication. The available concentration is 250 mg in 5 mL. Concentration = 250 mg / 5 mL = 50 mg/mL. Calculate the volume in milliliters (mL) to administer per dose. Volume (mL) = Dose per administration (mg) / Concentration (mg/mL) = 210.226 mg / 50 mg/mL = 4.2045 mL. Round the answer to the nearest tenth. = 4.2 mL.