METHODS	Blood for determination of plasma concentration of morphine ( M ) and its 3 - and 6-glucuronides ( M3G , M6G ) was collected , and area under the plasma concentration-time curve ( AUC ) 0-12 h , peak plasma concentration ( Cmax ) , time to reach Cmax ( tmax ) , and CO and C12 of M , M6G and M3G were determined on day 5 and day 10 .\