CYP2C19 metabolizer status (clopidogrel & others)

CYP2C19 activates the anti-clotting drug clopidogrel (Plavix) and clears several others, including some antidepressants, acid-reflux PPIs and the antifungal voriconazole. Two common variants set your speed: *2 switches the enzyme off and *17 speeds it up. Reading both together gives your overall metabolizer status, the way clinical dosing does, rather than judging one variant alone.

What CYP2C19 does

CYP2C19 is a liver enzyme that activates some drugs and clears others, which makes the direction of its effect depend entirely on which drug you are taking. The panel reads the two commonest variants: *2, which produces no working enzyme, and *17, which increases expression.

That gives a spectrum from poor metabolizer, with two non-functional copies, through intermediate and normal, to rapid and ultrarapid with one or two *17 copies.

Clopidogrel, where the direction is counterintuitive

Clopidogrel is a prodrug: it does nothing until CYP2C19 converts it into its active form. Poor metabolizers therefore get less antiplatelet effect, not more, and have higher rates of cardiovascular events after stenting and acute coronary syndromes.

The FDA added a boxed warning to clopidogrel in 2010 on exactly this point, and CPIC's 2022 guideline recommends considering an alternative antiplatelet such as prasugrel or ticagrelor for poor metabolizers undergoing percutaneous coronary intervention, where there is no contraindication. Poor metabolizers make up roughly 2% of white, 4% of Black and 14% of Chinese populations.

The other drugs this enzyme governs

Proton pump inhibitors such as omeprazole are cleared by CYP2C19, so ultrarapid metabolizers can get less acid suppression at standard doses, and poor metabolizers more. Several antidepressants, including citalopram, escitalopram and sertraline, are also substrates, and CPIC publishes guidance for them. Voriconazole, an antifungal, has a CPIC guideline as well and is one of the clearer cases.

The pattern to notice is that the same genotype means opposite things depending on whether the drug needs activating, as clopidogrel does, or clearing, as the others do.

The gap this panel has in East Asian ancestry

The *3 allele, another complete loss-of-function variant, is common in East Asian populations and rare elsewhere, and it is not read here. Someone of East Asian ancestry carrying *3 would be classified as a normal metabolizer by this panel while actually being intermediate or poor.

That matters because poor metabolizer status is most common in exactly that group. Clinical CYP2C19 panels include *3, which is one reason a consumer result should not be treated as a substitute.

What this panel does not tell you

It cannot tell you whether clopidogrel is working, which platelet function testing addresses directly, and it does not cover the many other reasons antiplatelet therapy succeeds or fails, including adherence, interacting drugs and the reason it was prescribed.

No one should change or stop an antiplatelet drug on a consumer genotype. Stopping clopidogrel after stenting carries serious risk, and any change belongs with the cardiologist who prescribed it.

What each CYP2C19 result means

Poor metabolizer (CYP2C19*2 ×2). You have two non-working copies of CYP2C19 (*2/*2), so you're a poor metabolizer. You activate very little of the anti-clotting drug clopidogrel (Plavix), so it may protect you much less, and doctors often choose a different antiplatelet drug. The flip side is that some other CYP2C19-cleared drugs (certain antidepressants, acid-reflux PPIs) can build up to higher levels. Worth flagging if any of these are ever prescribed.

Intermediate metabolizer (CYP2C19*2 ≥1). You carry one non-working copy of CYP2C19 (*2), making you an intermediate metabolizer. You activate the anti-clotting drug clopidogrel less well than usual, so it may protect you a bit less and an alternative is sometimes considered. This mainly matters around clopidogrel and a few other CYP2C19 drugs.

Normal metabolizer. You carry the standard versions of CYP2C19 (no *2 or *17), so you're a normal metabolizer: you activate clopidogrel and clear the other CYP2C19 drugs at the usual rate, and standard dosing generally fits. A few rarer CYP2C19 variants are not tested here.

Rapid metabolizer (CYP2C19*17 ≥1). You carry one increased-function copy of CYP2C19 (*17), making you a rapid metabolizer. You activate the anti-clotting drug clopidogrel well, and you clear some other CYP2C19 drugs a little faster than average. This is mostly favorable for clopidogrel and only occasionally relevant for other medicines.

Ultrarapid metabolizer (CYP2C19*17 ×2). You have two increased-function copies of CYP2C19 (*17/*17), making you an ultrarapid metabolizer. You activate clopidogrel very efficiently (fine, even helpful, for that drug), but you also clear some other CYP2C19 drugs quickly, so standard doses of certain acid-reflux PPIs, antidepressants or the antifungal voriconazole may run low. Worth knowing if those are prescribed.

Evidence & sources

This panel reads CYP2C19*2 (rs4244285) and CYP2C19*17 (rs12248560).

Reads the two most common CYP2C19 variants: the loss-of-function *2 and the increased-function *17. Together they classify most people of European ancestry, but rarer no-function alleles (*3, common in East Asians, plus *4 to *8) are not tested, so a 'normal', 'rapid' or 'ultrarapid' result does not fully rule them out.

CPIC provides dosing guidance for clopidogrel based on this gene.

Common questions

Does this mean clopidogrel will not work for me? Poor metabolizers get less of the active drug and have higher event rates in studies, which is why guidelines suggest considering prasugrel or ticagrelor instead in some settings. It is a prescribing decision, and stopping an antiplatelet drug on your own after a stent is dangerous.

Does this affect my omeprazole? It can, in the opposite direction to clopidogrel. Ultrarapid metabolizers clear proton pump inhibitors faster and may get less acid suppression at a standard dose, while poor metabolizers get more effect. This is a well-documented pharmacology rather than a reason to change a dose yourself.

Related

Drug acetylation speed (NAT2) · Efavirenz / drug metabolism (CYP2B6*6) · Gilbert syndrome (UGT1A1 gene) · Hepatitis C treatment response (IL28B) · Statin-induced myopathy risk · Tacrolimus metabolism (CYP3A5 gene) · Thiopurine metabolism (TPMT and NUDT15 genes)