What is the safe daily dosage of phenytoin for a child weighing 18 kg, given the recommended dosage of 5 mg/kg/day?

To determine the safe daily dosage of phenytoin for a child weighing 18 kg, you multiply the child's weight by the recommended dosage of 5 mg/kg/day.

Calculating this gives:

18 kg * 5 mg/kg/day = 90 mg/day.

This indicates that the safe daily dosage for a child of this weight is 90 mg. The correct answer effectively translates the dosage recommendation into a specific amount that matches the child's weight, ensuring that the administration of the drug is appropriate and within safe limits based on official guidelines.

In this case, the other options provided do not align with the calculated dosage. They either underdose or overdose the medication, which could lead to ineffective treatment or increased risk of side effects, emphasizing the importance of using the correct calculation.