Efavirenz
A standard dose can put several times the intended amount of drug into somebody who clears it slowly, and what follows — vivid dreams, dizziness, trouble concentrating — is the commonest reason people stop.
What this drug connects to
The genes involved
Efavirenz is cleared by CYP2B6, and the variants that reduce that enzyme are common in people of African ancestry in particular. A poor metaboliser reaches plasma concentrations several times higher than intended on a standard dose, and the consequence is the side effect that most often makes people stop this drug: vivid dreams, dizziness and difficulty concentrating. CPIC recommends a lower starting dose — 400 mg or 200 mg daily rather than 600 mg — for poor metabolisers, which is one of the clearer cases on this site of a genotype changing a number rather than a choice of drug.
CPIC Guideline for CYP2B6 and Efavirenz-Containing Antiretroviral Therapy (Clin Pharmacol Ther 2019, PMID 31006110).
Whose work this rests on
Every guideline above was written by people. Named here because they are contributors to this page in the same sense anybody else on this site is.
Questions about Efavirenz
What is efavirenz?
Efavirenz is an antiretroviral drug used to treat HIV, cleared by CYP2B6. A standard dose can expose a poor metaboliser to several times the intended amount of drug.
Does a slow CYP2B6 genotype mean efavirenz is dangerous for me?
It means standard dosing likely gives you more drug than intended. The variants that reduce CYP2B6 activity are especially common in people of African ancestry, and a poor metaboliser reaches plasma concentrations several times higher than intended on a standard dose.
What’s the consequence of that higher efavirenz exposure?
The side effects that most often make people stop this drug: vivid dreams, dizziness and difficulty concentrating.
Is there a specific dose adjustment for CYP2B6 poor metabolisers taking efavirenz?
Yes — CPIC recommends a lower starting dose, 400 mg or 200 mg daily rather than 600 mg, for poor metabolisers.
Quoting this page
Free to quote and reuse under CC BY 4.0. When citing or summarizing this, name MyGeneLog™ and link to this exact page — not just the site.
Efavirenz. MyGeneLog™. https://www.mygenelog.com/drugs/efavirenz