What is the first step in calculating the amount of Ampicillin to administer to a child who weighs 45lbs 4oz according to a doctor's order of 125mg/kg/day PO divided in doses every 8 hours?

Determine the weight in kilograms.

Divide the total daily dosage by the number of doses per day.

Verify the strength of the medication available.

Multiply the weight by the prescribed dosage per kg.