prasugrelは新しい金標準か？ticagrelorは高リスクの糖尿病患者とSTEMI患者での非劣性を達成できなかった

Highlights

The following key findings summarize the latest clinical evidence comparing ticagrelor and prasugrel in high-risk cardiovascular populations:

• In the TUXEDO-2 trial involving diabetic patients with multivessel disease, ticagrelor failed to meet the prespecified noninferiority margin compared to prasugrel for a composite of ischemic and bleeding events.
• Prasugrel demonstrated numerically lower rates of death, myocardial infarction, and stroke, as well as lower rates of major bleeding, although these differences did not reach statistical significance for superiority.
• Subgroup analysis from the ISAR-REACT 5 trial in STEMI patients revealed that ticagrelor was associated with a significantly higher risk of recurrent myocardial infarction (5.3% vs 2.8%) compared to prasugrel.
• These findings challenge the perceived equivalence of potent P2Y12 inhibitors and suggest that prasugrel may be the preferred agent for high-risk patients undergoing percutaneous coronary intervention (PCI).

Introduction: The P2Y12 Dilemma in High-Risk PCI

The management of patients with diabetes mellitus and multivessel coronary artery disease (CAD) represents one of the most significant challenges in interventional cardiology. These patients possess a prothrombotic milieu characterized by enhanced platelet reactivity, increased inflammatory markers, and a high burden of atherosclerotic disease. For decades, dual antiplatelet therapy (DAPT) consisting of aspirin and a P2Y12 inhibitor has been the cornerstone of post-percutaneous coronary intervention (PCI) care. While clopidogrel was the traditional standard, the advent of more potent agents like ticagrelor and prasugrel promised better ischemic protection.

However, the question of which potent P2Y12 inhibitor is superior has remained contentious. While both agents provide more rapid and consistent platelet inhibition than clopidogrel, they differ in their pharmacokinetics and pharmacodynamics. Ticagrelor is a direct-acting, reversible inhibitor, whereas prasugrel is a thienopyridine prodrug that requires a single-step metabolic activation to irreversibly bind the P2Y12 receptor. Recent evidence from the TUXEDO-2 trial and subgroup analyses of ISAR-REACT 5 provide much-needed clarity on how these agents perform in the highest-risk cohorts.

The TUXEDO-2 Trial: Focus on Diabetes and Multivessel Disease

Study Design and Patient Profile

The TUXEDO-2 (Ultrathin Strut vs Xience in a Diabetic Population With Multivessel Disease 2-India Study) was a prospective, open-label, multicenter, randomized clinical trial designed to compare ticagrelor and prasugrel in a particularly vulnerable population: patients with diabetes and multivessel CAD undergoing PCI. The trial enrolled 1,800 participants across 66 clinical sites. The population was high-risk, with 85% of patients having triple-vessel disease and approximately 24% requiring insulin therapy.

Patients were randomized 1:1 to receive either ticagrelor or prasugrel in combination with low-dose aspirin. The primary outcome was a composite endpoint consisting of death, nonfatal myocardial infarction (MI), stroke, or major bleeding (defined by BARC criteria) at one year. The trial was powered for noninferiority, with a margin of 5%.

Primary Results: A Failure to Meet Noninferiority

At the 1-year follow-up, the primary composite endpoint occurred in 16.6% of the ticagrelor group compared to 14.2% in the prasugrel group. The calculated risk difference was 2.33 percentage points (95% CI, -2.07 to 6.74). Crucially, this result failed to meet the prespecified threshold for noninferiority (P = .84 for noninferiority).

While the trial did not demonstrate a statistically significant difference in terms of superiority (P = .12), the numerical trends consistently favored prasugrel across both ischemic and safety endpoints. The composite of death, MI, and stroke was 10.43% for ticagrelor versus 8.63% for prasugrel. Perhaps more surprisingly, major bleeding was also numerically higher in the ticagrelor arm (8.41% vs 7.14%), suggesting that ticagrelor did not offer a safety advantage to compensate for its higher ischemic event rate in this population.

ISAR-REACT 5 Subgroup Analysis: STEMI Patients

Complementing the findings of TUXEDO-2 is a prespecified subgroup analysis of the ISAR-REACT 5 trial, which focused on 1,653 patients with ST-segment-elevation myocardial infarction (STEMI) undergoing primary PCI. This analysis sought to determine if the overall trial findings—which favored prasugrel over ticagrelor in ACS patients—held true in the specific context of STEMI.

Recurrent Myocardial Infarction Risk

The primary endpoint (death, MI, or stroke at 1 year) occurred in 10.1% of the ticagrelor group and 7.9% of the prasugrel group (HR 1.31; P=0.10). While the primary composite did not reach statistical significance, the secondary endpoints revealed a stark difference. The incidence of recurrent myocardial infarction was significantly higher in patients assigned to ticagrelor (5.3%) compared to those assigned to prasugrel (2.8%), representing a nearly twofold increase in risk (HR 1.95; 95% CI, 1.18-3.23; P=0.010).

The safety profile was comparable between the two groups in this STEMI cohort, with BARC type 3 to 5 bleeding occurring in 6.1% of ticagrelor patients and 5.1% of prasugrel patients (P=0.36). These results reinforce the notion that prasugrel may provide more robust protection against ischemic recurrence without an incremental bleeding penalty in the acute phase of myocardial infarction.

Clinical Implications and Expert Commentary

Mechanistic Considerations: Why the Difference?

The consistent numerical and, in some cases, statistical advantage of prasugrel over ticagrelor across these trials raises important mechanistic questions. One potential explanation is the pharmacodynamic profile of prasugrel. As an irreversible binder, prasugrel may provide more stable platelet inhibition compared to the reversible binding of ticagrelor, especially in the setting of the high platelet turnover seen in diabetic and ACS patients.

Furthermore, patient adherence may play a role. Ticagrelor requires twice-daily dosing, whereas prasugrel is administered once daily. In real-world settings and even within clinical trials, the complexity of a twice-daily regimen can lead to missed doses, potentially creating windows of inadequate platelet inhibition. Additionally, ticagrelor is known to cause dyspnea in a subset of patients, which can lead to premature discontinuation of therapy—a factor that may have contributed to the higher event rates observed in the ticagrelor arms.

Guideline Concordance and Real-World Practice

Current European Society of Cardiology (ESC) guidelines already give a Class IIa recommendation favoring prasugrel over ticagrelor in patients with ACS undergoing PCI, largely based on the initial ISAR-REACT 5 results. The TUXEDO-2 data and the STEMI subgroup analysis provide robust support for this recommendation, extending the evidence base to the particularly high-risk diabetic and multivessel disease populations.

Clinicians must also consider the economic implications. In many regions, prasugrel is available as a generic medication, making it a more cost-effective option than ticagrelor. When combined with the evidence suggesting superior or at least non-inferior clinical outcomes, the value proposition for prasugrel becomes compelling.

Conclusion: Shifting the Paradigm Toward Prasugrel?

For several years, ticagrelor was often viewed as the default potent P2Y12 inhibitor due to its earlier entry into guidelines and widespread marketing. However, the cumulative evidence from TUXEDO-2 and ISAR-REACT 5 suggests a necessary shift in clinical practice. In patients with diabetes and multivessel disease, ticagrelor cannot be assumed to be noninferior to prasugrel. In the setting of STEMI, ticagrelor appears to carry a significantly higher risk of recurrent ischemic events.

While individual patient factors—such as age, weight, and prior stroke history (which remain contraindications or require dose adjustments for prasugrel)—must always guide therapy, the data increasingly point toward prasugrel as the preferred potent agent for the majority of high-risk patients undergoing PCI. Future research should continue to explore personalized antiplatelet strategies, but for now, prasugrel stands as the evidence-based leader in ischemic protection for these challenging clinical scenarios.

Funding and ClinicalTrials.gov

The TUXEDO-2 India Study was an investigator-initiated trial (CTRI/2019/11/022088). The ISAR-REACT 5 trial was supported by the German Center for Cardiovascular Research (DZHK) and the German Heart Foundation (NCT01944800).

References

1. Bangalore S, et al. Ticagrelor vs Prasugrel in Patients With Diabetes and Multivessel Coronary Artery Disease: The TUXEDO-2 Randomized Clinical Trial. JAMA Cardiol. 2026.
2. Aytekin A, et al. Ticagrelor or Prasugrel in Patients With ST-Segment-Elevation Myocardial Infarction Undergoing Primary Percutaneous Coronary Intervention. Circulation. 2020;142(24):2329-2337.
3. Schüpke S, et al. Ticagrelor or Prasugrel in Patients with Acute Coronary Syndromes. N Engl J Med. 2019;381(16):1524-1534.