To identify risk factors that may predispose patients to rifampin- and cefazolin-induced coagulopathy.

An 86-year-old man with a history of rheumatoid arthritis on chronic prednisone and stage 3 chronic kidney disease, notably not on warfarin, presented to the hospital with a 10-day history of right hip pain, swelling, and drainage after a recent right total-hip arthroplasty. The patient underwent a combination of surgical intervention and medication therapy with rifampin and ceftriaxone. After discharge and at postoperative day 9, ceftriaxone was changed to cefazolin due to increasing alkaline phosphatase levels. Four weeks after the initial debridement, antibiotics, and implant retention, the patient underwent a second irrigation and debridement due to persistent infection. Cefazolin and rifampin therapy was extended. Three days later, the patient presented to the emergency room with significant bleeding at the surgical site and a profoundly elevated prothrombin time and international normalized ratio (INR). No potential contributors were identified. The Naranjo adverse drug reaction probability scale identified cefazolin and rifampin as the probable cause of elevated INR. The Liverpool adverse drug reaction avoidability assessment tool classified this adverse event as “definitely avoidable.”

Rifampin-containing regimens are often recommended to treat staphylococcal prosthetic joint infections when the implant is retained. In methicillin-susceptible staphylococcal infections, cefazolin is routinely employed as the β-lactam backbone of definitive antimicrobial regimens. Although rifampin- and cefazolin-induced hypoprothrombinemia seems to be rare, adverse consequences of its occurrence may be prevented with appropriate monitoring.