Is Welireg affected by genetics?

Yes — the active ingredient is metabolized by a gene known to vary between individuals.

Relevant genes: CYP2C19

Welireg is affected by pharmacogenetics through the CYP2C19 gene. Your genotype for this gene can change how your body processes Welireg, which can affect both how well it works and how well you tolerate it. The strongest evidence level on this page is Moderate, based on CPIC or FDA guidelines.

What's in Welireg

belzutifan affected by CYP2C19

Affected by CYP2C19 · FDA · Moderate evidence

Read the full belzutifan genetics guide →

Belzutifan phenotype recommendations

Published guidance from FDA on how belzutifan should be dosed or substituted based on your CYP2C19 phenotype.

Phenotype	What it means	Recommendation	Evidence
Ultrarapid Metabolizer CYP2C19	Your body processes belzutifan at a normal rate. The standard dose should work as expected.	FDA Initiate therapy with recommended starting dose.	—
Rapid Metabolizer CYP2C19	Your body processes belzutifan at a normal rate. The standard dose should work as expected.	FDA Initiate therapy with recommended starting dose.	—
Normal Metabolizer CYP2C19	Your body processes belzutifan at a normal rate. The standard dose should work as expected.	FDA Initiate therapy with recommended starting dose.	—
Intermediate Metabolizer CYP2C19	Your body processes belzutifan at a normal rate. The standard dose should work as expected.	FDA Initiate therapy with recommended starting dose.	—
Poor Metabolizer CYP2C19	Your body breaks down belzutifan more slowly than normal, causing higher drug levels. This increases the risk of side effects like anemia and low oxygen levels, so closer monitoring is needed.	FDA Initiate at standard dose with enhanced monitoring for anemia and hypoxia due to higher systemic concentrations.	Moderate
Likely Intermediate Metabolizer CYP2C19	Your body likely processes belzutifan at a near-normal rate. The standard dose should work as expected.	FDA Initiate therapy with recommended starting dose.	—
Likely Poor Metabolizer CYP2C19	Your body likely breaks down belzutifan more slowly than normal, causing higher drug levels. This increases the risk of side effects like anemia and low oxygen levels, so closer monitoring is needed.	FDA Initiate at standard dose with enhanced monitoring for anemia and hypoxia due to higher systemic concentrations.	Moderate
Indeterminate CYP2C19	The impact of your genotype on response to this drug is unknown	FDA Initiate therapy with recommended starting dose.	—
Not available CYP2C19	The impact of your genotype on response to this drug is unknown	FDA Initiate therapy with recommended starting dose.	—

Source: FDA

The gene behind the guidance

CYP2C19 Cytochrome P450 2C19

CYP2C19 handles several SSRIs (citalopram, escitalopram, sertraline), proton pump inhibitors (omeprazole, esomeprazole), and the blood thinner clopidogrel. About 2 to 5 percent of people of European descent and 15 to 20 percent of people of East Asian descent are poor metabolizers. Another 30 percent carry a rapid-metabolizer variant.

Rapid metabolizers clear affected drugs before they reach therapeutic levels. Poor metabolizers accumulate the drug and feel stronger effects.

See all drugs affected by CYP2C19 →

Browse the full drug-class: Chemotherapy agents.

Related medications

Find out how your genetics affect Welireg

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.

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Informational 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.