This research study will determine if genetic variation in CYP2B6 affects how the body metabolizes methadone.

This investigation determined the influence of CYP2B6 genetic variation, specifically CYP2B6*6 polymorphism, on clinical methadone plasma concentrations, clearance, and metabolism. The hypothesis was that CYP2B6*6 heterozygotes or homozygotes would have reduced metabolism and clearance. A secondary objective was to evaluate other less common genotypic variants, when encountered. Healthy volunteers in genotype cohorts CYP2B6*1/*1, CYP2B6*1/*6 , and CYP2B6*6/*6, and also CYP2B6*4 and CYP2B6*5 carriers, received single doses of IV and oral methadone. Plasma and urine methadone and metabolite concentrations were determined by tandem mass spectrometry. The primary outcome measure was methadone metabolism, measured as plasma metabolite/patent area under the concentration-time curve ratio and metabolite formation clearance.

Inclusion Criteria:

Each subject must meet all of the following criteria:

• 18-50 yr old
• CYP2B6*1/*1, CYP2B6*1/*6 or CYP2B6*6/*6 genotype
• Good general health with no remarkable medical conditions
• BMI < 33
• Provided informed consent

Exclusion Criteria:

Subjects will not be enrolled if any of the following criteria exist:

• Known history of liver or kidney disease
• Use of prescription or non prescription medications, herbals or foods known to be metabolized by or affect CYP2B6
• Females who are pregnant or nursing
• Known history of drug or alcohol addiction (prior or present addiction or treatment for addiction)
• Direct physical access to and routine handling of addicting drugs in the regular course of duty (this is a routine exclusion from studies of drugs with addiction potential)

3 subjects with non-evaluable PK data