Fig. 7. Time course of buprenorphine concentration in plasma (  dashed line ) and biophase (  solid line ) in a typical healthy volunteer after intravenous bolus administration of 0.4 mg/70 kg buprenorphine. The  dotted line represents the apparent  in vivo fractional receptor occupancy of buprenorphine. The elimination of buprenorphine from brain is slower than from plasma. The  thick dashed–dotted line represents the K^Dvalue of 1.244 ng/ml. Note that most observed buprenorphine concentrations are below the estimated K^Dvalue.