Final answer:
The nurse manager's first action should be to communicate with the assigned nurse to verify the client's claim about not receiving medications and understand the reasons behind it.
Step-by-step explanation:
When a client informs the nurse manager that they have not received their medications throughout the shift, the first action the nurse manager should take is to communicate: discuss the client's statement with the assigned nurse. This initial step is crucial as it allows the nurse manager to gather information regarding the situation before making any changes or taking further action. It's important to verify the client's statement, understand why this occurred, and ensure the client receives their medication promptly while maintaining a professional and respectful approach.