Which medication would be a poor choice for controlling diabetes in a patient with heart failure?

Pioglitazone, which is a thiazolidinedione, is associated with fluid retention and weight gain, both of which can exacerbate heart failure symptoms. This medication works by increasing insulin sensitivity but may lead to increased sodium retention, which can worsen edema and heart failure status. The use of pioglitazone in patients with existing heart failure is typically avoided or approached with caution due to these potential side effects.

In contrast, other medications such as exenatide, glyburide, and insulin may not have the same degree of adverse effects related to heart failure. Exenatide, as a GLP-1 receptor agonist, generally has a favorable safety profile in this regard. Glyburide, a sulfonylurea, acts by increasing insulin secretion from the pancreas and, while it requires monitoring for hypoglycemia, is not primarily associated with fluid retention. Insulin is also commonly used in managing diabetes without the same risk of fluid retention as thiazolidinediones.

Thus, pioglitazone's mechanism and associated risks make it a poor choice for controlling diabetes in a patient with heart failure.