Final answer:
Before administering metoprolol, a beta blocker for hypertension, the nurse must measure the patient's vital signs to ensure safe medication administration.
Step-by-step explanation:
The priority assessment a nurse should make before administering the beta blocker metoprolol (Lopressor) to a patient with hypertension is to measure the vital signs. This is crucial because beta blockers can significantly affect heart rate and blood pressure. Measuring vital signs, particularly blood pressure and heart rate, provides essential information on the patient's cardiovascular status and helps ensure the safe administration of the medication.