Chapter 12 FIG. 3. A plasma concentration-effect plot for pain relief (VAS) data from a cancer patient who received a continuous intravenous infusion (20 mg/hr) of morphine sulfate. The solid line indicates data obtained during the infusion, the arrow indicates the point at which the infusion was discontinued, and the broken line indicates data collected during the postinfusion phase. Note the counterclockwise hysteresis (lag loop) for pain relief produced by morphine. (From ref. 9.) Click here to see the graphic at a different resolution