Weekly warfarin dosage, INR values, and concurrent rifampin therapy over time. The x-axis represents time in relation to the dates of the patient’s anticoagulation clinic appointments. The left y-axis represents the prescribed warfarin dosage in milligrams/week, which is shown by the vertical bars. The right y-axis represents the INR values, which are depicted by the black points (therapeutic range: 2.0-3.0). The time period of the concurrent rifampin therapy is shown as a horizontal dark bar.