We describe a 79-year-old man with spondylodiscitis and unknown pathogen, treated with cefazolin and rifampicin. He developed a massive digestive hemorrhage. Prothrombin time was prolonged with severe vitamin-K-dependent clotting-factor deficiency. Severe bleeding can occur during cefazolin and rifampicin use. This deficiency should be assessed before prescribing cefazolin-rifampicin and prothrombin time monitored.