A nurse is caring for four clients. After administering morning medications, she realizes that the nifedipine prescribed for one client was inadvertently administered to another client. Which of the following actions should the nurse take first?

The correct answer is D: Check the client's vital signs. The first action the nurse should take is to assess the client's vital signs to monitor for any potential adverse effects of the medication. Nifedipine is a calcium channel blocker that can cause hypotension and other cardiovascular effects. By checking the vital signs first, the nurse can promptly identify any signs of distress and take immediate action to ensure the client's safety. This step is crucial in prioritizing the client's well-being and addressing any potential harm caused by the medication error.

Summary:
A: Filling out an occurrence form can be done later but is not the immediate priority.
B: Administering the medication to the correct client is not appropriate as it may cause harm.
C: Notifying the client's provider is important but not as urgent as assessing the client's vital signs.
D: Checking the client's vital signs is the first and most critical step to ensure client safety.