When administering phenytoin at 100 mg, how many mL of a suspension at 125 mg/5 mL should a nurse prepare?

To determine the volume of the phenytoin suspension needed to administer a dose of 100 mg, it is essential to use the concentration of the suspension, which is 125 mg in 5 mL.

First, calculate how many mg are present in 1 mL of the suspension:

125 mg / 5 mL = 25 mg/mL.

Next, to find out how many mL are required to achieve the desired dose of 100 mg, use the following proportion:

100 mg ÷ 25 mg/mL = 4 mL.

This calculation indicates that to deliver 100 mg of phenytoin, the nurse must prepare 4 mL of the suspension. Therefore, the correct answer is associated with this calculated volume of 4 mL, confirming that the nurse should prepare this amount to ensure the patient receives the appropriate dosage.