Yes — the active ingredient is metabolized by a gene known to vary between individuals.
Relevant genes: HLA-B
Used for: HIV infection (as part of combination antiretroviral therapy)Ziagen (abacavir) is a foundational example of how pharmacogenetics has changed prescribing practice. Shortly after abacavir was introduced for HIV treatment, a hypersensitivity reaction was identified in roughly 5 to 8 percent of patients, sometimes severe enough to be fatal on re-exposure. In 2008, a large prospective study established that screening for a single HLA allele, HLA-B*57:01, before starting abacavir could nearly eliminate the reaction. The FDA immediately updated the abacavir label to recommend universal pre-prescribing genetic screening. Since then, HLA-B*57:01 testing has become a de facto requirement before starting any abacavir-containing regimen (including the fixed-dose combinations Epzicom, Trizivir, and Triumeq).
Abacavir itself is a nucleoside reverse transcriptase inhibitor with standard antiviral pharmacology. The HLA-B*57:01 association isn't about how the drug is metabolized; it's about how the immune system recognizes abacavir-modified peptides on cell surfaces. In carriers, the reaction typically develops within 6 weeks of starting the drug and presents with fever, rash, gastrointestinal symptoms, and respiratory complaints. Re-exposure after a reaction can be rapidly fatal. Screening is essentially 100 percent sensitive: patients who test negative for HLA-B*57:01 do not develop the reaction.
Read the full abacavir genetics guide →Published guidance from FDA on how abacavir should be dosed or substituted based on your HLA-B phenotype.
| Phenotype | What it means | Recommendation | Evidence |
|---|---|---|---|
|
*57:01
HLA-B
|
You carry a gene variant that puts you at high risk for a serious allergic reaction to abacavir. This drug should not be used. |
FDA
Do not use abacavir in patients positive for HLA-B*57:01 due to risk of serious hypersensitivity reaction.
|
Strong |
Source: FDA
HLA-B variants don't affect how drugs are metabolized. They affect your immune system's reaction to them. Specific HLA-B alleles are strongly linked to severe skin reactions to drugs like abacavir (HIV), carbamazepine (seizures, bipolar), and allopurinol (gout).
Screening for HLA-B*57:01 before abacavir, and HLA-B*15:02 before carbamazepine in at-risk populations, is now standard of care in much of the world.
If you've been prescribed an abacavir-containing HIV regimen, your HLA-B*57:01 result should already be on file before you fill the prescription. If you're ever offered abacavir again after a prior abacavir-associated reaction, do not take it, even briefly. The re-exposure reaction is much more severe than the first one and has been fatal in documented cases. The HLA-B*57:01 test is one of the cleanest wins in clinical pharmacogenetics: cheap, fast, and it actually changes outcomes.
All patients who may be prescribed abacavir, yes. Because abacavir is used in so many first-line and fixed-dose combinations, testing is effectively routine for anyone starting treatment. Patients on regimens that don't include abacavir (such as tenofovir-based combinations) don't strictly need the test, but many HIV clinics order it proactively to preserve flexibility in future regimen changes.
No. Once a patient has had an abacavir hypersensitivity reaction, they should be considered allergic for life, regardless of what any subsequent HLA testing shows. The HLA-B*57:01 test is for prospective risk stratification, not for clearing a patient who has already reacted.
Prevalence varies by ancestry. It's present in about 5 to 8 percent of people of European descent, around 2 percent of people of African descent, and less than 1 percent of most East Asian populations. No population has zero prevalence, so universal screening is the clinical standard rather than ancestry-based testing.
This page describes the general pharmacogenetics. A Gene2Rx report analyzes your own DNA to tell you which metabolizer group you fall into, across every medication.
Get your report Look up another medicationInformational only — not medical advice. Pharmacogenetic guidance describes population-level patterns; your individual response depends on many factors. Never start, stop, or change a medication without talking to your prescribing clinician.