Which medication can increase the risk of gastrointestinal bleeding when used with warfarin?

The correct choice is associated with the potential increase in gastrointestinal bleeding risk when used concurrently with warfarin. Proton Pump Inhibitors (PPIs) are medications used to reduce stomach acid production. While PPIs are often prescribed to protect the gastric mucosa in patients taking warfarin, they have been shown to interact with the metabolism of warfarin and may affect its anticoagulant effect.

Warfarin's effectiveness is monitored through its effect on the INR (International Normalized Ratio), and any changes in its absorption or metabolism can lead to increased risks of bleeding, including in the gastrointestinal tract. Although the primary purpose of PPIs is to prevent bleeding by mitigating ulcer formation, their interaction with warfarin can ultimately lead to an increased risk when the warfarin's anticoagulant effect is altered—making the patient more susceptible to bleeding complications when other risk factors are also present.

The other medications listed do not have the same direct impact on the risk of gastrointestinal bleeding when used with warfarin, either due to their mechanisms of action or because they do not significantly alter warfarin metabolism or effect on coagulation.