What is the relative risk reduction in nonfatal myocardial infarction (MI) for patients treated with prasugrel (prasugrel) compared to clopidogrel (clopidogrel)?

Relative Risk Reduction in Nonfatal MI with Prasugrel vs Clopidogrel

Patients treated with prasugrel were 23% less likely to experience a nonfatal MI than patients treated with clopidogrel.

Understanding the Data

The TRITON-TIMI 38 trial compared prasugrel to clopidogrel in patients with acute coronary syndrome undergoing percutaneous coronary intervention. Looking at the data presented:

• Nonfatal MI occurred in 7.3% of patients in the prasugrel group versus 9.5% in the clopidogrel group
• The hazard ratio (HR) was 0.77 (95% CI: 0.67-0.85)

Calculating Relative Risk Reduction

The relative risk reduction (RRR) is calculated using the formula: RRR = (1 - Hazard Ratio) × 100%

In this case: RRR = (1 - 0.77) × 100% = 23%

This means prasugrel reduced the relative risk of nonfatal MI by 23% compared to clopidogrel 1.

Clinical Context of the Finding

This 23% relative risk reduction in nonfatal MI was a key component of the overall benefit seen with prasugrel:

• The primary composite endpoint (cardiovascular death, nonfatal MI, or nonfatal stroke) was reduced by 19% (HR 0.81; 95% CI: 0.73-0.90) 1
• The benefit was primarily driven by the reduction in nonfatal MI 1
• The reduction in MI was evident both early (within first 3 days) and later (beyond 3 days) 2

Important Clinical Considerations

While prasugrel showed superior efficacy in reducing nonfatal MI, this benefit must be balanced against increased bleeding risk:

• Major bleeding was significantly higher with prasugrel (2.4% vs 1.8%; HR 1.32; 95% CI: 1.03-1.68) 1
• Fatal bleeding was also higher with prasugrel (0.4% vs 0.1%; p=0.002) 1

Special Populations with Unfavorable Risk-Benefit Profile

Three subgroups did not have favorable outcomes with prasugrel 1:

• Patients with prior stroke/TIA (contraindicated)
• Patients ≥75 years of age (no net benefit)
• Patients with body weight <60 kg (no net benefit)

Conclusion on Relative Risk Reduction

The correct interpretation of the data is that prasugrel treatment resulted in a 23% relative risk reduction in nonfatal MI compared to clopidogrel. This represents a clinically significant reduction in a key component of the primary endpoint, but must be considered alongside the increased bleeding risk when making treatment decisions.