CYP2C9*3 — markedly reduced warfarin metabolism
One copy of the CYP2C9*3 reduced-function variant detected.
You have one working copy and one much-less-active copy of the CYP2C9 gene.
Intermediate to poor metabolizer for warfarin. Dose reduction is typical; clinical INR monitoring is essential.
Your body clears the blood-thinner warfarin much more slowly than average. If you're ever prescribed it, your doctor will reduce the dose and watch your blood-clotting levels (INR) carefully.
What this means
*3 has a larger effect on enzyme activity than *2 and is the more clinically important of the two reduced-function CYP2C9 alleles. Phenytoin sensitivity is also increased — *3 carriers can develop toxicity at standard doses. Sulfonylurea (gliclazide, glipizide) clearance is reduced, increasing hypoglycemia risk.
The *3 version of the CYP2C9 gene has a larger effect than the *2 version — it produces an enzyme that's substantially less active. That matters most for the blood-thinner warfarin, where carriers need much lower doses than average to avoid bleeding. The anti-seizure drug phenytoin also builds up and can reach toxic levels at a standard dose. And some diabetes medicines (gliclazide, glipizide) clear from your system more slowly, which can push blood sugar too low. All of this is important information for a doctor prescribing any of these medicines.
Caveats
- Most relevant if warfarin, phenytoin, or sulfonylureas are prescribed.
- The clinical effect is highly actionable but only if a prescriber knows about it.
- Combining with VKORC1 status improves warfarin dose estimates.