In which instance should a nurse be most concerned when a client is prescribed a beta-blocker?

A nurse should be particularly concerned when a client has a heart rate that is below the normal range and is prescribed a beta-blocker. Beta-blockers are primarily used to manage conditions such as hypertension, heart rhythm disorders, and heart failure by slowing the heart rate and decreasing the workload on the heart. If a client's heart rate is already low, administering a beta-blocker could exacerbate bradycardia, potentially leading to serious health complications such as fainting or worsening heart function.

In contrast, while elevated blood pressure is a common reason for prescribing a beta-blocker, it is not an immediate concern if the drug is deemed appropriate for that condition. Fatigue can be a side effect of beta-blockers, but it doesn't necessarily indicate a need for immediate intervention. Lastly, while a client expressing a desire to exercise is important for creating a well-rounded health plan, it would not create as urgent a concern in the context of beta-blocker therapy as a significantly low heart rate would. Therefore, monitoring the heart rate is critical, making it the most immediate concern in this scenario.