A nurse is planning to administer a controlled substance to a client who is experiencing pain. Which of the following actions should the nurse plan to take first?

The correct answer is C: Identify the client using two identifiers. This should be the first action because it ensures the right medication is being given to the right patient, which is crucial for patient safety. By confirming the client's identity with two identifiers (such as name and date of birth), the nurse minimizes the risk of medication errors. Documenting the administration of the medication (A) should come after ensuring the correct patient is receiving it. Comparing medication amounts to inventory (B) and removing medication from the cabinet (D) are important steps but not as critical as confirming the patient's identity.