Which of the following medications poses a significant risk to patients with heart failure?

In patients with heart failure, certain medications can exacerbate the condition or lead to adverse effects. Ephedrine is a sympathomimetic agent that can increase heart rate and blood pressure by stimulating the cardiovascular system. This stimulation can lead to increased myocardial oxygen demand, which is detrimental for patients with heart failure who already have compromised cardiac function. The use of such stimulants is risky because they can exacerbate symptoms, increase the workload on the heart, and potentially lead to heart failure exacerbation.

The other medications listed do not carry the same level of risk for exacerbating heart failure symptoms. Acetaminophen is generally safe in patients with heart failure as it does not impact cardiovascular function. Metformin is used for managing diabetes and has a favorable safety profile in heart failure patients, although caution is advised in cases of renal impairment. Ibuprofen, while it can pose risks due to its nonsteroidal anti-inflammatory properties, primarily in terms of fluid retention and potential kidney effects, does not have the immediate stimulatory effects on the heart that ephedrine does. Therefore, it is crucial for healthcare providers to avoid using ephedrine in patients with heart failure to prevent any exacerbations of their condition.