Yes — the active ingredient is metabolized by a gene known to vary between individuals.
Relevant genes: DPYD
carac is affected by pharmacogenetics through the DPYD gene. Your genotype for this gene can change how your body processes carac, which can affect both how well it works and how well you tolerate it. The strongest evidence level on this page is Strong, based on CPIC or FDA guidelines.
Published guidance from CPIC and FDA on how fluorouracil should be dosed or substituted based on your DPYD phenotype.
| Phenotype | What it means | Recommendation | Evidence |
|---|---|---|---|
|
Normal Metabolizer
DPYD
|
"Your genetic test shows you have a normal ability to process the drug fluorouracil. This means you are at typical risk of side effects, and your doctor is likely to suggest the standard dosage." |
CPIC
Based on genotype, there is no indication to change dose or therapy. Use label-recommended dosage and administration
FDA
Initiate therapy with recommended starting dose.
|
Strong |
|
Intermediate Metabolizer
DPYD
|
"Your genetic test indicates that your body might process the drug fluorouracil more slowly, potentially increasing side effects. Therefore, your doctor may start you on a lower dose and then adjust it based on your body's response to the medicine." |
CPIC + CPIC
Reduce starting dose by 50% followed by titration of dose based on toxicity or therapeutic drug monitoring (if available).
Patients with the c.[2846A>T];[2846A>T] genotype may require >50% reduction in starting dose.
FDA
Use with extreme caution. No safe dose has been established. Withhold or discontinue if severe side effects occur.
|
Strong |
|
Poor Metabolizer
DPYD
|
"Your genetic results suggest that your body may not process the medication fluorouracil as expected, leading to strong side effects. Your doctor may choose not to use this drug, or if there is no suitable alternative, they may lower the dose and monitor its effect closely." |
CPIC + CPIC
Activity score 0.5: Avoid use of 5- fluorouracil or 5-fluorouracil prodrug-based regimens. In the event, based on clinical advice, alternative agents are not considered a suitable therapeutic option, 5-fluorouracil should be administered at a strongly reduced dose with early therapeutic drug monitoring.l
Activity score 0: Avoid use of 5-fluorouracil or 5-fluorouracil prodrug-based regimens.
FDA
Do not use fluorouracil. No safe dose exists for poor metabolizers. Use an alternative treatment.
|
Strong |
|
Indeterminate
DPYD
|
The impact of your genotype on response to this drug is unknown |
CPIC + FDA
Initiate therapy with recommended starting dose.
|
— |
|
Not available
DPYD
|
The impact of your genotype on response to this drug is unknown |
CPIC + FDA
Initiate therapy with recommended starting dose.
|
— |
DPYD breaks down fluoropyrimidine chemotherapy drugs (5-FU, capecitabine). A small percentage of people carry reduced-function variants that cause the drug to accumulate to toxic levels. This is one of the few pharmacogenetic tests that is mandatory in many oncology guidelines before starting treatment.
Partial DPYD deficiency calls for a 25 to 50 percent dose reduction. Complete deficiency is a contraindication: standard-dose fluoropyrimidine can be fatal.
Browse the full drug-class: Chemotherapy agents.
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.