Efavirenz (brand name Sustiva) is a non-nucleoside reverse transcriptase inhibitor (NNRTI) used as part of antiretroviral therapy for HIV-1 infection.
It is commonly prescribed in combination with other agents to suppress viral replication and improve immune function in adults and children with HIV-1.
Efavirenz works by binding directly to the reverse transcriptase enzyme, causing a conformational change that inhibits viral DNA synthesis and prevents HIV from multiplying.
The CYP2B6 gene encodes an enzyme primarily responsible for metabolizing efavirenz in the liver. CYP2B6 activity varies between individuals depending on genetic variants, affecting how quickly the drug is processed.
Individuals with high‐activity variants of CYP2B6 may clear efavirenz faster, reducing drug exposure, while those with low‐activity variants may experience higher blood levels and an increased risk of side effects. Metabolizer status is categorized into groups based on combined genetic changes.
Variations in CYP2B6 produce distinct metabolizer phenotypes—ultrarapid, rapid, normal, intermediate, poor, and indeterminate—which influence efavirenz concentrations. Ultrarapid and rapid metabolizers may have lower drug levels and reduced efficacy risk, whereas intermediate and poor metabolizers have higher levels, leading to an increased likelihood of central nervous system adverse effects.
Want to know what your genetics say about how you'll respond to Efavirenz?
A Gene2Rx report reads your own DNA to show how it may affect your response to Efavirenz and your other medications.
{# data-track routes these through the sitewide cta_click listener in base.html, which attaches page_type / drug_name / guide_slug from the server-resolved page context. This one file instruments the mid-article CTA on ~114 content pages. #} Find out todayThe following dosing guidelines are based on the CPIC recommendations for efavirenz metabolism by CYP2B6.
| Phenotype | Clinical Consequence | Guideline Recommendation |
|---|---|---|
| Ultrarapid Metabolizer | Slightly lower efavirenz concentrations; potential subtherapeutic exposure | Initiate efavirenz with standard dosing (600 mg/day) |
| Rapid Metabolizer | Slightly lower efavirenz concentrations | Initiate efavirenz with standard dosing (600 mg/day) |
| Normal Metabolizer | Expected efavirenz metabolism | Initiate efavirenz with standard dosing (600 mg/day) |
| Intermediate Metabolizer | Higher efavirenz concentrations; increased risk of CNS adverse events | Consider initiating efavirenz with decreased dose of 400 mg/day |
| Poor Metabolizer | Significantly higher efavirenz concentrations; high CNS toxicity risk | Consider initiating efavirenz with decreased dose of 400 mg or 200 mg/day |
| Indeterminate / Not available | Unknown impact | Initiate therapy with recommended starting dose (600 mg/day) |
The CPIC and FDA guidelines do not provide specific alternative drug recommendations for efavirenz. Clinicians may consider other antiretroviral agents (e.g., nevirapine, integrase inhibitors) based on individual patient factors and resistance profiles.
See the full list of drugs affected by each gene:
See how your genetics affect each product Efavirenz shows up in:
Interested in learning more about how your genetics may affect your response to medication? Get started with Gene2Rx today.
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