<qa>  What is the CYP2B6 gene associated with?This proposed investigation will test the following hypotheses: 1 Enzymatic activity of CYP2B6 characterized by the formation clearance of methadone to EDDP CLf,EDDP, is directly related to both gestational and postnatal age; 2 variations in the CYP2B6 gene SNPs are associated with variable activity of the CYP2B6 enzyme as measured by the formation clearance, CLf,EDDP, and 3 the elimination rate of methadone and its major metabolite EDDP in neonates is dependent on the glomerular filtration rate and therefore on the stage of development defined by both gestational and postnatal age. The investigators propose to develop a PK model for methadone dosing in neonates that takes into account both developmental stage and genetic variability. The long-term goal of the proposed investigations is to improve dosing of methadone in neonates exposed to opioids in utero or post-natally, leading to improved control of their withdrawal syndrome and decreased adverse drug reactions associated with the current use of methadone in these vulnerable patients. More immediately, the investigators will develop a PK model for methadone dosing based on relevant developmental and genetic characteristics. The acquired knowledge based on the proposed study will lead to a more efficacious treatment of pain or opiate withdrawal syndrome in newborn infants with a decreased chance of adverse drug reactions. 