Prior to administering metoprolol tartrate (Lopressor), a nurse should measure which parameter?

• A. Urine output
• B. Capillary refill
• C. Body weight
• D. Heart rate

Answer: (D)

Metoprolol tartrate is a beta-blocker that slows the heart rate and reduces myocardial contractility. Before giving it, you need a baseline heart rate because a low pulse indicates the drug could push the heart rate into bradycardia and potentially lower cardiac output. If the heart rate is too slow (for example, below about 60 bpm) you would typically hold the dose and reassess or notify the prescriber.

Urine output, capillary refill, and body weight don’t directly reflect how this medication will affect cardiac rhythm or conduction, so they’re not the primary safety check for a beta-blocker at the bedside. The heart rate is the key parameter to monitor to prevent an adverse effect and to guide safe administration.