Final answer:
0.5 mL of naloxone should be administered.
Step-by-step explanation:
To calculate the amount of naloxone (narcan) to be administered, we can use the following formula:
Amount (mL) = Dose ordered (mg) / Concentration (mg/mL)
Plugging in the values:
Amount (mL) = 0.2 mg / 0.4 mg/mL
Amount (mL) = 0.5 mL
Therefore, 0.5 mL of naloxone should be administered.