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

Angiotensin-converting enzyme (ACE) inhibitors reduce mortality in patients with heart failure and coronary artery disease. Recently, there has been growing concern about the possible interaction between ACE inhibitors and aspirin. Numerous investigators have addressed this issue; however, results are equivocal. Most researchers used a statistical test of interaction, but the use of this method has been criticized. To assess the interaction between ACE inhibitors and aspirin properly, an additive model-more specifically, the Rothman Synergy Index-should be used. Further investigation with this model, however, is needed.