What is the nurse's first action after realizing a medication error was made with phenytoin instead of meperidine?

The first action for the nurse after realizing that a medication error has occurred, such as administering phenytoin instead of meperidine, is to check the client's vital signs. This action is critical because it assesses the immediate impact of the medication error on the patient's physiological status.

In the case of a medication like phenytoin, which is an anticonvulsant, the patient could experience adverse effects that might compromise their health, including changes in vital signs like blood pressure, heart rate, or respiratory status. By establishing a baseline of the client’s current condition, the nurse can provide necessary information for further evaluation and treatment.

Checking the vital signs also allows the nurse to quickly identify any urgent changes that may require immediate intervention, which is essential for ensuring patient safety. After assessing the patient's condition, the nurse can then take appropriate further steps, such as notifying the healthcare provider or administering the correct medication if it is indicated after the assessment.