The Lancet JUNE 26, 2021

Aspirin versus clopidogrel for chronic maintenance monotherapy after percutaneous coronary intervention (HOST-EXAM)

Hyo-Soo Kim, Jeehoon Kang, Kyung-Woo Park, et al.

Bottom Line

The HOST-EXAM trial demonstrated that clopidogrel monotherapy is superior to aspirin monotherapy for the secondary prevention of major adverse clinical events in patients who have completed an initial period of dual antiplatelet therapy after drug-eluting stent implantation.

Key Findings

1. Clopidogrel monotherapy significantly reduced the risk of the primary composite endpoint (all-cause death, non-fatal myocardial infarction, stroke, readmission due to acute coronary syndrome, and BARC type ≥3 bleeding) compared to aspirin monotherapy (5.7% vs 7.7%; hazard ratio [HR] 0.73; 95% CI 0.59–0.90; p=0.0035).

2. The superior efficacy of clopidogrel was driven by reductions in both thrombotic events (3.7% vs 5.5%; HR 0.68) and bleeding complications (2.3% vs 3.3%; HR 0.69) compared to the aspirin group.

3. The observed treatment benefit of clopidogrel over aspirin remained consistent during long-term extended follow-up (median 5.8 years), suggesting a durable clinical advantage for indefinite maintenance monotherapy.

4. All-cause mortality was numerically similar between the two groups, indicating that the primary benefit of clopidogrel monotherapy is the reduction of major non-fatal clinical and bleeding events.

Study Design

Design

RCT

Open-Label

Sample

5,438

Patients

Duration

24 mo

Median

Setting

Multicenter, South Korea

Population Patients aged ≥20 years who underwent PCI with drug-eluting stents and were event-free after 6-18 months of dual antiplatelet therapy.

Intervention Clopidogrel 75 mg once daily

Comparator Aspirin 100 mg once daily

Outcome Composite of all-cause death, non-fatal myocardial infarction, stroke, readmission due to acute coronary syndrome, and Bleeding Academic Research Consortium (BARC) type ≥3 bleeding.

Study Limitations

• The trial was conducted as an open-label study, which introduces potential bias in the reporting of clinical events.

• The study population was exclusively East Asian, which may limit the generalizability of these findings to other ethnic or global populations due to potential differences in pharmacogenomic profiles and baseline event rates.

• The post-trial follow-up period relied on physician discretion for the choice of antiplatelet agent, potentially introducing variability and confounding in the long-term data analysis.

• The study was not originally powered for specific subgroup analyses, such as distinguishing between ACS and non-ACS presentations or high bleeding risk versus non-high bleeding risk cohorts.

Clinical Significance

The HOST-EXAM trial provides robust evidence to challenge the long-standing reliance on aspirin as the default agent for indefinite monotherapy following coronary stenting, suggesting clopidogrel as a safer and more effective alternative for chronic secondary prevention in this population.

Historical Context

Following the widespread adoption of drug-eluting stents (DES), standard of care dictated dual antiplatelet therapy followed by indefinite aspirin monotherapy. However, the optimal agent for long-term maintenance remained debated due to inconsistent data on efficacy and bleeding risks. HOST-EXAM represents the first large-scale, randomized, head-to-head trial in the contemporary DES era to specifically evaluate this maintenance strategy.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

How do the mechanisms of action for aspirin and clopidogrel differ regarding their inhibition of platelet activation, and why might clopidogrel's target be particularly relevant for preventing arterial thrombosis post-stenting?

Key Response

Aspirin irreversibly inhibits the cyclooxygenase-1 (COX-1) enzyme, preventing the synthesis of thromboxane A2. Clopidogrel is a prodrug that irreversibly blocks the P2Y12 adenosine diphosphate (ADP) receptor. Because the ADP pathway is a central amplifier of platelet activation regardless of the initial trigger, P2Y12 inhibition may provide more potent and comprehensive protection against stent-related and systemic atherothrombotic events than COX-1 inhibition alone.

Resident

In a patient who has completed 12 months of dual antiplatelet therapy (DAPT) after a drug-eluting stent (DES) without any adverse events, what specific clinical benefits did the HOST-EXAM trial identify for switching to clopidogrel monotherapy versus continuing aspirin monotherapy?

Key Response

The HOST-EXAM trial found that clopidogrel monotherapy was superior to aspirin monotherapy for the primary composite endpoint of all-cause death, non-fatal MI, stroke, readmission for ACS, and BARC bleeding type 2 or greater. Notably, clopidogrel reduced both ischemic events and bleeding complications, offering a superior net clinical benefit for long-term maintenance.

Fellow

The HOST-EXAM trial addressed the 'maintenance' phase of antiplatelet therapy. How do these findings complement or contrast with 'aspirin-free' strategies explored in trials like TWILIGHT or TICO, which focused on the early post-PCI period?

Key Response

TWILIGHT and TICO examined the safety of dropping aspirin early (at 3 months) in favor of P2Y12 inhibitor monotherapy (specifically ticagrelor) to reduce bleeding during the high-risk first year. HOST-EXAM extends this 'aspirin-free' concept into the chronic phase (beyond 6-18 months), suggesting that even after the initial high-risk period, clopidogrel remains a more effective and safer monotherapy than the historical standard of aspirin.

Attending

Despite the significant findings of the HOST-EXAM trial, why has clopidogrel not yet universally replaced aspirin as the 'default' lifelong monotherapy in your clinical practice, and what patient-specific factors might still favor aspirin?

Key Response

Resistance to changing the aspirin-for-life paradigm stems from its long-term safety record, extreme low cost, and the fact that HOST-EXAM was conducted entirely in South Korea. The 'East Asian Paradox' (where patients have higher platelet reactivity but lower ischemic risk) may limit the generalizability of these findings to Western populations. Factors favoring aspirin might include known clopidogrel resistance/CYP2C19 loss-of-function alleles or the need for a cheaper, once-daily medication with a longer established history in primary and secondary prevention across multiple vascular beds.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

Critically analyze the HOST-EXAM study's use of a 'Net Clinical Benefit' composite endpoint. What are the statistical and interpretative risks of combining disparate outcomes like 'bleeding' and 'all-cause death' into a single primary measure?

Key Response

Composite endpoints assume all components have equal clinical significance, which is rarely true (e.g., a BARC 2 bleed is not equivalent to a stroke). While net clinical benefit provides a global view of treatment impact, it can mask 'directionally discordant' results where a drug reduces one event type but increases another. Researchers must use sensitivity analyses and report individual components to ensure the benefit isn't driven solely by less severe endpoints, such as minor bleeding or re-hospitalization.

Journal Editor

As a peer reviewer for a high-impact journal, how would you address the potential for 'ascertainment bias' in an open-label trial like HOST-EXAM, and does the use of a blinded clinical events committee (CEC) sufficiently mitigate this concern?

Key Response

The open-label design is a significant threat to internal validity, as both patients and clinicians knew the treatment assignment, which could influence the reporting of softer endpoints like 'readmission for ACS' or 'bleeding.' While a blinded CEC helps standardize event adjudication, they can only adjudicate the events that are actually reported by the unblinded site investigators, potentially leaving the trial vulnerable to reporting bias.

Guideline Committee

Current ACC/AHA and ESC guidelines generally recommend aspirin monotherapy (Class I) indefinitely after DAPT. Based on HOST-EXAM and the subsequent HOST-EXAM Extended study, what level of evidence and class of recommendation would you propose for clopidogrel monotherapy in the chronic maintenance phase?

Key Response

The HOST-EXAM trial provides Level of Evidence A (large RCT) evidence for clopidogrel's superiority in the East Asian population. However, because it is a single-region study, a Class IIa (Should be considered) recommendation for clopidogrel monotherapy may be more appropriate than a Class I (Strongly recommended) until results are replicated in a more diverse global cohort. Currently, the 2021 ACC/AHA/SCAI guidelines still favor aspirin but acknowledge P2Y12 monotherapy as a reasonable alternative.

Clinical Landscape

Noteworthy Related Trials

1996

CAPRIE Trial

n = 19,185 · Lancet

Tested

Clopidogrel 75mg daily

Population

Patients with recent myocardial infarction, stroke, or established peripheral arterial disease

Comparator

Aspirin 325mg daily

Endpoint

Composite of ischemic stroke, myocardial infarction, or vascular death

Key result: Clopidogrel was found to be slightly more effective than aspirin in reducing the risk of a combined endpoint of ischemic stroke, myocardial infarction, or vascular death.

2006

CHARISMA Trial

n = 15,603 · NEJM

Tested

Clopidogrel plus aspirin

Population

Patients with cardiovascular disease or multiple risk factors

Comparator

Aspirin plus placebo

Endpoint

Composite of myocardial infarction, stroke, or cardiovascular death

Key result: The addition of clopidogrel to aspirin did not provide a significant benefit in reducing the rate of cardiovascular events compared to aspirin alone in the overall population.

2015

PEGASUS-TIMI 54 Trial

n = 21,162 · NEJM

Tested

Ticagrelor (60mg or 90mg twice daily) plus aspirin

Population

Patients with a history of myocardial infarction and additional high-risk features

Comparator

Placebo plus aspirin

Endpoint

Composite of cardiovascular death, myocardial infarction, or stroke

Key result: Long-term treatment with ticagrelor added to low-dose aspirin significantly reduced the risk of major cardiovascular events, though it increased the risk of major bleeding.

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