Response to Letters Regarding Article, “Drug Resistance and Pseudoresistance: An Unintended Consequence of Enteric Coating Aspirin”
We thank the authors of the letters for their interest in our publication.1
True aspirin drug resistance would be expected to be (1) specific for aspirin, (2) reflected by incomplete inhibition of the molecular target of aspirin, and (3) a relatively stable phenotype that is reproducible when assessed on multiple occasions. It is this last point that we refer to when we conclude that a single time measurement may be insufficient to diagnose aspirin resistance.
Whereas most published studies, including the studies by Dillinger, Drouet, and Henry, assessed the incidence of aspirin nonresponsiveness only on 1 occasion, we showed that retesting individuals under identical conditions after a washout period of 2 weeks may result in surprisingly inconsistent observations. Approximately 37% of those who were nonresponders on the first aspirin exposure converted to being responders on the second occasion. Approximately 10% of the responders on the first occasion were nonresponders on the second aspirin exposure. Individuals who switch response status within just a few weeks cannot be considered truly aspirin resistant.
Dillinger, Drouet, and Henry have not assessed occasion-to-occasion variability in the response status in their study populations using the proposed single 24-hour measurement. Determining both the sensitivity and the false-positive rate for identifying aspirin resistance using a single-occasion measurement would be a prerequisite to evaluating the utility of such an approach.
Tilo Grosser, MD
Susanne Fries, MD
John A. Lawson, MS
Shiv C. Kapoor, PhD
Gregory R. Grant, PhD
Garret A. FitzGerald, MD
Institute for Translational Medicine and Therapeutics, Perelman School of Medicine
University of Pennsylvania
T.G. received consultancy fees from PLx Pharma. G.A.F. received research funding from Bayer Health Care to support partial funding of this study. The other authors report no conflicts.
- © 2013 American Heart Association, Inc.