What is a key safety alert associated with warfarin use?

The key safety alert associated with warfarin use is gastrointestinal bleeding. Warfarin is an anticoagulant medication that increases the risk of bleeding. This is a significant concern because it can lead to serious and potentially life-threatening complications. Patients taking warfarin must be closely monitored for any signs of bleeding, particularly gastrointestinal bleeding, which can manifest as abdominal pain, nausea, vomiting blood, or the presence of blood in the stool.

The other options, while they may be associated with other conditions or medications, do not represent the primary safety concern focused on with warfarin use. For instance, calciphylaxis relates more to patients with significant renal impairment or those on dialysis, kidney failure is more a consequence of underlying conditions rather than a direct alert associated with warfarin itself, and heart attacks are influenced by various cardiovascular factors unrelated to the specific effects of warfarin.