Figure 11-13 Mean plasma concentrations (± SEM) of morphine, morphine-6-glucuronide (M-6-G), and morphine-3-glucuronide (M-3-G) after intravenous and oral administration of morphine. (From Osborne R, Joel S, Trew D, Slevin M: Morphine and metabolite behavior after different routes of morphine administration: demonstration of the importance of the active metabolite morphine-6-glucuronide. Clin Pharmacol Ther 47:12–9, 1990.)