UGT1A1

Drugs affected by UGT1A1

UDP Glucuronosyltransferase Family 1 Member A1

6 medications 9 brand products

About UGT1A1

UGT1A1 clears bilirubin (the molecule that builds up in jaundice) and several drugs including irinotecan and nilotinib.^[1] A variant called *28, common in people of all ancestries, reduces UGT1A1 activity. It's the cause of Gilbert's syndrome, a benign condition, but it also makes cancer patients much more susceptible to severe side effects from irinotecan-based chemotherapy.^[2]

Oncology dosing of irinotecan is often adjusted down for patients carrying two copies of the UGT1A1*28 variant.

What we test for UGT1A1

Gene2Rx uses definitions covering 8 named UGT1A1 star alleles, built from 7 variants in Gene2Rx definitions. Results depend on the variants available in your upload.

Star alleles

Defined variants

Gene2Rx definitions

Source

GRCh38

Genome build

Normal Function 2 Increased Function 1 Decreased Function 4 Unknown Function 1

Notable UGT1A1 alleles

*1 Normal Function

Reference allele — normal UGT1A1 glucuronidation activity.

*28 Decreased Function

A decreased-function TA-repeat allele linked to Gilbert syndrome and irinotecan neutropenia.

~35% in Europeans

*6 Decreased Function

A decreased-function missense allele common in East Asian populations.

What are star alleles?

Star alleles (like *1, *2, *4) are standardized names for distinct versions of a pharmacogene. *1 is the reference; other numbers identify distinct allele definitions. A higher number does not mean lower function.

You inherit one allele from each parent, so your genotype is a pair (e.g. *1/*4). The pair determines your predicted phenotype — for example, whether you metabolize a drug at a normal, decreased, or no-function rate.

PharmVar is the international registry that defines and curates these allele names. Gene2Rx uses the supported definitions summarized here. Coverage depends on the variants present in your input; this is not a guarantee that every cataloged allele can be identified.

Medications with UGT1A1 information

This list contains 6 medications with UGT1A1 information from the sources shown below. Evidence and report eligibility differ by drug; each page explains its scope and limitations.

antiretrovirals

Atazanavir CPIC

chemotherapies →

Belinostat FDA Irinotecan FDA Nilotinib FDA Pazopanib FDA Sacituzumab Govitecan Hziy FDA

Brand products containing a UGT1A1-affected ingredient

These branded medications include at least one active ingredient whose metabolism or action involves UGT1A1. Each links to its full pharmacogenetic breakdown.

sacituzumab govitecan-hziy

Votrient

pazopanib

References

U.S. Food and Drug Administration. Table of Pharmacogenomic Biomarkers in Drug Labeling (2024). fda.gov
PharmGKB / Stanford University. PharmGKB: The Pharmacogenomics Knowledge Base. pharmgkb.org

Explore UGT1A1 in your report

A Gene2Rx report interprets supported variants in the context of your data and purchased report. Missing or uncertain calls may prevent an assessment.

Get your report Look up a medication

Informational only, not medical advice. The presence of a UGT1A1 pharmacogenetic guideline does not mean every patient needs to change their dose. Never start, stop, or change a medication without talking to your prescribing clinician.