Which cephalosporin should not be prescribed to a patient taking Coumadin?

Ceftriaxone is the cephalosporin that should be avoided in a patient taking Coumadin, primarily due to its potential to displace warfarin from its protein-binding sites. Warfarin is highly protein-bound, and when displaced, it can lead to increased free levels of warfarin in the bloodstream, thus heightening the risk of bleeding complications.

Additionally, ceftriaxone can also have effects on vitamin K metabolism and may interfere with the coagulation process, further complicating the management of patients on anticoagulants like Coumadin.

While other cephalosporins such as cefazolin, cefepime, and cefuroxime may have a lower risk of these interactions, ceftriaxone's distinctive pharmacokinetic profile poses a significant risk, necessitating caution or avoidance in patients on anticoagulant therapy.