Efavirenz / drug metabolism (CYP2B6*6)

CYP2B6 breaks down several medicines, including the HIV drug efavirenz, the antidepressant bupropion, and methadone. A common variant (*6) lowers its activity, so these drugs can build up to higher levels in carriers.

Possible results

Normal CYP2B6 activity. You have the normal-function version of CYP2B6, the enzyme that breaks down drugs like the HIV medicine efavirenz, bupropion and methadone. You clear them at the usual rate, so standard dosing generally fits.

Reduced CYP2B6 activity. You carry one reduced-function (*6) copy of CYP2B6, so you break down efavirenz and some other drugs a bit more slowly, which can raise their blood levels. It mainly matters if you take those specific medicines, where a lower dose is sometimes considered.

Low CYP2B6 activity. You have two reduced-function (*6) copies of CYP2B6, so drugs like efavirenz can build up to noticeably higher levels and cause more side effects. If you're ever prescribed efavirenz (or bupropion, methadone), this is worth flagging, since a lower dose may be appropriate.

Evidence & sources

Across global populations, about 7% of people carry two copies of this variant, and about 56% carry none.

CPIC provides dosing guidance for efavirenz based on this gene.

Related

Abacavir hypersensitivity (HLA-B*57:01) · CYP2C19 metabolizer status (clopidogrel & others) · Fluoropyrimidine (5-FU) toxicity risk · Hepatitis C treatment response (IL28B) · Opioid receptor response (OPRM1 A118G) · Thiopurine metabolism (TPMT and NUDT15 genes) · Warfarin dose sensitivity