DISCUSSION: Rivaroxaban is one of the newer agents that has revolutionized the approach to treatment of VTE in recent years. Bioavailability of Rivaroxaban is dose dependent and the metabolism of rivaroxaban is mediated by CYP3A4. Beside the drug interactions submitted to the FDA by manufacturers, there is paucity of published trials or case reports of drug interactions especially between Rifampin (a CYP3A4 inducer) and Rivaroxaban. Our case highlights a critical issue pertaining to use of Rivaroxaban and use of CYP3A4 inducer. Although, our patient had no apparent contra-indication to use of rivaroxaban; he was on Rifampin for hip infection which may have decreased the concentration of Rivaroxaban. Although dose adjustment is suggested; higher dose of Rivaroxaban is not approved by FDA at this time. The indication for monitoring of drug levels of newer anticoagulants remains a matter of ongoing discussion and target therapeutic ranges are not established nor validated. While traditional anticoagulant, warfarin, is also reported to have several drug interactions; the ability to monitor its effect makes it a reasonable option.