Weight-based dosing (e.g., mg/kg/day) is common for pediatric patients. The daily dose is calculated by multiplying 2 mg/kg/day x 45 kg (the child’s weight) = 90 mg/day; the kg units cancel each other out. Note that in this case, the patient’s weight is provided in kilograms, which matches the weight-based dosing calculation; if the patient’s weight was listed in pounds, then converting from pounds to kilograms would have been necessary before plugging numbers into the equation.