CYP2B6 metabolizes about 10% of all drugs in current clinical use. There is strong evidence that certain genetic variants may affect the metabolism of efavirenz (Sustiva®), bupropion (Wellbutrin SR®), and methadone (Dolophine®). Patients who are initiating these therapies, or have a history of adverse effects or treatment failure, should be considered for CYP2B6 genotyping. CYP2B6 is primarily expressed in the liver and is involved in the first-pass metabolism of ingested drugs. It has also been detected in several tissues outside the liver, including the brain, kidney, and intestine.  Clinically relevant genetic alleles tested for CYP2B6 are *2,*4,*5,*6,*7,*9,*16,*18, and *28.
Indication for CYP2B6 Testing
Patients with a personal or family history of adverse drug reactions or treatment failures to efavirenz, bupropion, methadone, or other medications metabolized by CYP2B6 are good candidates for testing. CYP2B6 genotyping is also useful to confirm or rule out the presence of genetic variations that may impact how a patient will metabolize the medications above.
Testing may potentially allow prescribers to optimize efavirenz therapy, better predict bupropion efficacy, and identify methadone users at increased risk of developing QTc prolongation.