Quantifying the interaction between angiotensin-converting enzyme inhibitors and aspirin: are we using the right method?

Does Aspirin Attenuate the Beneficial Effect of ACE Inhibitors in Elderly People with Heart Failure?

BACKGROUND

Several studies have raised concerns over a possible reduction in the beneficial effects of ACE inhibitors on mortality in people also taking aspirin (acetylsalicylic acid).

OBJECTIVE

We performed this study to determine whether there is a reduction in the beneficial effects of ACE inhibitors on mortality in elderly people with heart failure also taking aspirin.

PARTICIPANTS

822 patients discharged from hospital wards with a diagnosis of heart failure participated in the GIFA (Italian Group of Pharmacoepidemiology in the Elderly) study.

MEASUREMENTS

We analysed the characteristics of the participants according to the type of therapy prescribed (no ACE inhibitor/no aspirin, ACE inhibitor/no aspirin, no ACE inhibitor/aspirin and ACE inhibitor/aspirin). We calculated the hazard ratios (HRs) for dying associated with each of these treatments, and calculated the synergy index to identify any negative interaction between ACE inhibitor and aspirin.

RESULTS

The mean age of study participants was 79 +/- 7.3 (SD) years. Of the 629 (76.5%) patients discharged on ACE inhibitor and/or aspirin therapy, 31.0% were taking both drugs. Compared with no therapy with ACE inhibitor or aspirin, the HR for death was 0.65 (95% CI 0.31, 1.36) for aspirin users, 0.45 (95% CI 0.27, 0.74) for ACE inhibitor users and 0.37 (95% CI 0.19, 0.70) for ACE inhibitor/aspirin users. The synergy index was 0.98 (95% CI 0.34, 2.80), suggesting no interaction between the drugs.

CONCLUSIONS

Our data do not support the existence of a negative interaction between ACE inhibitors and aspirin in elderly patients with heart failure.