Reviews/P2Y12 Antiplatelets/CYP2C19 loss-of-function alleles increase MACE risk with clopidogrel after PCI
Genotype · P2Y12-CYP-01 · v1
Borderline: within 4 points of the Established/Likely boundary, so a re-grade could land either side.
Clopidogrel must be activated by the liver enzyme CYP2C19, and some people carry gene variants that make this enzyme work poorly. The question is whether those people have more heart events after a stent procedure. Across one randomised genetic substudy in heart-attack patients [7] and four separate real-world studies [6][10][14][15][16], carriers of the poorly-working gene variants had more adverse cardiac events, especially clots forming in the stent, with risks roughly 1.5 to 2.3 times higher. The signal is clearest for stent clots and softer for the broader mix of heart events. One stent study [17] found the gene did not predict events once platelet activity was measured directly, and a randomised test in a different patient group [1] found no gene-related difference. The panel treated the association as well supported but tempered by these caveats and by the fact that most of the supporting studies were observational.
In stented and post-heart-attack populations, a randomised genetic substudy [7] reported carriers had a 53% higher rate of the composite of cardiovascular death, myocardial infarction, or stroke (hazard ratio 1.53, 95% CI 1.07 to 2.19) and roughly a threefold higher stent thrombosis risk (hazard ratio 3.09, 95% CI 1.19 to 8.00). Four observational studies agree in direction: post-MI cohort [6] (HR 2.26, 1.15 to 4.41), an East Asian drug-eluting-stent cohort [10] (adjusted HR 1.89, 1.20 to 2.91 for MACCE), an electronic-health-record case-control [14] (HR 1.54, 1.16 to 2.06), an early-stent-thrombosis case-control [15] (OR 1.99, 1.47 to 2.69), and a Chinese stent cohort [16] where one-year stent thrombosis rose from 0.88% in extensive metabolizers to 10.0% in poor metabolizers. The effect is most consistent for the stent-thrombosis component. Counter-evidence comes from [17], where poor metabolizers were not at increased stent thrombosis (2.7% vs 2.5%) or MACE risk and platelet phenotyping outpredicted genotype, and from [1], which found no clopidogrel-by-genotype interaction. The contested point: The division is whether a genotype-to-MACE causal effect holds beyond stent thrombosis and independently of measured platelet reactivity. Most supportive studies are observational [6][10][14][15][16] with residual-confounding risk, [17] nulls the signal in a PCI cohort once platelet function is measured, and the one randomised interaction test [1] was null, albeit in an ACS/AF rather than PCI population.
All 18 papers behind this claim with their DOIs and what each does to it, the panel’s arbitration, the evidence gap map and the open research questions. Free, and sent to your inbox.
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The strongest confirmatory evidence outside the single RCT substudy [7] is observational ([6][10][14][15][16]) and vulnerable to unadjusted confounding; causal attribution of MACE to genotype is weaker than the HRs suggest.
The effect is concentrated in stent thrombosis, a narrower endpoint than the 'MACE' in the claim; broad all-cause MACE support ([10] MACCE, [6] composite) is softer and in [17] absent.
Where it remains uncertain. In the PCI cohort [17] poor metabolizers showed no excess risk (stent thrombosis 2.7% vs 2.5%) and platelet phenotyping outperformed genotyping, while the randomised interaction test in [1] was null.
Aleatory
Stent thrombosis is infrequent, so counts are small and intervals wide, e.g. the stent-thrombosis hazard ratio in [7] spans 1.19 to 8.00.
Epistemic
Four of five supportive studies [6][10][14][15][16] are non-randomised, leaving residual confounding that genotype-outcome associations cannot fully exclude.
Inferential
In [17] measured platelet reactivity predicted events while genotype did not, so inferring a genotype-driven MACE effect may misattribute a phenotype signal.
The load-bearing papers from a corpus of 18, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
Counter-evidence from a randomised placebo-controlled test: no clopidogrel-by-LoF interaction in ACS/AF (non-PCI population).
“The effect of clopidogrel in reducing the rate of the primary efficacy outcome was similar in patients who were heterozygous or homozygous for loss-of-function alleles and in those who were not carriers of the alleles (rate among carriers, 8.0% with clopidogrel vs. 11.6% with placebo; hazard ratio with clopidogrel, 0.69; 95% confidence interval [CI], 0.49 to 0.98; rate among noncarriers, 9.5% vs. 13.0%; hazard ratio, 0.72; 95% CI, 0.59 to 0.87).”
Panel auditInternal validity: high · scope of inference: ACS and atrial fibrillation patients, not a PCI-defined population; addresses clopidogrel-vs-placebo efficacy modification rather than carrier-vs-noncarrier MACE after PCI.Key limitations: not a PCI-specific cohort · design is clopidogrel vs placebo, not carrier vs noncarrier MACE · includes atrial fibrillation patients
Post-MI cohort showing LoF carriage associated with increased MACE under clopidogrel.
“CYP2C19 loss-of-function but not PON1 variants were significantly associated with increased risk of major cardiovascular events (death, MI, and urgent coronary revascularization) occurring during long-term clopidogrel exposure in 371 young post-MI patients (age <45 years) enrolled in the AFIJI cohort (CYP2C19 loss-of-function allele carrier versus noncarrier: hazard ratio, 2.26; 95% confidence interval, 1.15-4.41, P=0.02”
Panel auditInternal validity: medium · scope of inference: Young (<45 years) post-MI patients on long-term clopidogrel; MACE by genotype, with PCI not specified.Key limitations: post-MI cohort not defined as PCI · young selected population · observational
Randomised-trial genetic substudy in ACS largely managed with PCI directly linking LoF carriage to higher MACE and stent thrombosis.
“Among clopidogrel-treated subjects in TRITON-TIMI 38, carriers had a relative increase of 53% in the composite primary efficacy outcome of the risk of death from cardiovascular causes, myocardial infarction, or stroke, as compared with noncarriers (12.1% vs. 8.0%; hazard ratio for carriers, 1.53; 95% confidence interval [CI], 1.07 to 2.19; P=0.01) and an increase by a factor of 3 in the risk of stent thrombosis (2.6% vs. 0.8%; hazard ratio, 3.09; 95% CI, 1.19 to 8.00; P=0.02).”
Panel auditInternal validity: high · scope of inference: ACS patients treated with clopidogrel in TRITON-TIMI 38 (invasively managed); MACE and stent thrombosis by genotype.Key limitations: genetic subgroup is observational within the trial · PCI proportion not quantified in abstract
Counter-evidence: in a PCI cohort genotype was not predictive of stent thrombosis or MACE once platelet function was assessed.
“whereas poor metabolizers (CYP2C19*1/*2 or *2/*2 carriers) were not at increased risks (stent thrombosis, 2.7% vs. 2.5%, P > 0.05; MACE, 13.5% vs. 12.1%, P = 0.556)”
Panel auditInternal validity: medium · scope of inference: PCI patients on clopidogrel; comparison of phenotyping versus CYP2C19 genotyping for predicting stent thrombosis and MACE.Key limitations: single cohort · low event counts · modest sample
4 of 18 papers shown. The full review lists all of them, with the panel’s arbitration →
Claims are graded at each quarterly release, and re-graded between releases only when a pivotal trial lands. Every change is a new version of the claim.
Multiple independent primary studies in PCI populations support the association with consistent direction and mechanism, but residual confounding, one null PCI cohort, and endpoint narrowness keep it at high-Likely rather than Established.
Release 2026-q4 re-graded every claim from its corpus under protocol v0.19. An earlier release's grade is shown for the record; it came from an earlier protocol and is not a movement.
Assumptions that carry weight but are not themselves established.
The panel records the gap that would most move the claim, and the study that would close it.
Randomised genotype-by-clopidogrel interaction test in PCI. The only randomised interaction test [1] is in ACS/AF and null; the PCI support is observational apart from [7], so causal effect modification in PCI is unconfirmed. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: A randomised trial in PCI patients comparing clopidogrel against an alternative P2Y12 inhibitor, prespecified for genotype-by-treatment interaction on MACE.
Open question: Does CYP2C19 loss-of-function carriage increase broad all-cause MACE after PCI, or chiefly the stent-thrombosis component? Why it is still open: The corpus shows the firmest effect on stent thrombosis [7][15][16] while broader MACCE/composite support [6][10] is softer and [17] is null.
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 21 Oct 2026 · protocol v0.19