Suspected interaction: warfarin and erythromycin.

The patient described had a markedly enhanced response to warfarin when he was given erythromycin concomitantly. Before the initiation of erythromycin, his warfarin anticoagulation had been well controlled. After withdrawal of erythromycin, his response to warfarin returned to normal. These findings and previously reported clinical and laboratory data lead to the conclusion that, at least in some patients, a potentially serious interaction between erythromycin and warfarin can occur.