Figure 1. The mean (+/- SD; n = 20) plasma concentration-time profiles of morphine (upper panel), M-6-G (middle), and morphine-3-glucuronide (lower panel) after intravenous administration of morphine and M-6-G. Dosage A ([circle, open]): M-6-G-bolus of 0.015 mg/kg plus infusion of 0.0072 mg [center dot] kg sup -1 [center dot] h sup -1, dosage B ([square, open]): M-6-G-bolus of 0.029 mg/kg plus infusion of 0.014 mg [center dot] kg sup -1 [center dot] h sup -1, dosage C (open triangle): M-6-G-bolus of 0.044 mg/kg plus infusion of 0.022 mg [center dot] kg sup -1 [center dot] h sup -1, dosage D ([lozenge, filled]): morphine-bolus of 0.14 mg/kg plus infusion of 0.05 mg [center dot] kg sup -1 [center dot] h sup -1 for 4 h, dosage E (closed inverted triangle): M-6-G combined with morphine (doses A + D). After administration of M-6-G, neither morphine-3-glucuronide nor morphine was detected in plasma. Note the different scaling of the ordinates for clarification.