Fig. 1

This graph represents the daily warfarin dose, INR, and concomitant rifampin therapy over time. The x-axis represents time when the INR was measured. The left y-axis represents the INR units and is shown by the black diamond points. The right Y-axis represents warfarin dose administered in milligrams/day and is shown by the vertical bars. The therapeutic range is indicated between the two dotted lines (2.5–3.5). The time period of concomitant rifampin administration is shown as the horizontal solid 2-way arrow