We oppose the recommendation of Otero and Schmitt and others to exclude events related to error from the definition of adverse drug reactions. Doing so would significantly alter the meaning of a term used for decades by the pharmacovigilance community, including regulatory agencies worldwide. Adoption of these new definitions would force agencies to revise regulations and would diminish capacity to analyze trends in rates of adverse drug reactions. The additional complexity of classification also risks exacerbating underreporting of adverse drug reactions by clinicians.

The distinction proposed by Otero and Schmitt and others has logical flaws. Regardless of whether an error is judged to be present, harm due to a drug is always caused in part by the drug's intrinsic properties. Stipulating lack of preventability as central to the definition of adverse drug reactions also tends to increase rather than decrease confusion. One problem with defining error and preventability as exactly equivalent is that not all errors are preventable, given the intrinsic limitations of human-designed systems and behaviors. Furthermore, as human errors are conceptualized in current scientific and ethical contexts, many reactions that are currently judged to be unavoidable or acceptable may later be found to be avoidable, unacceptable, or both. The exclusive focus on error, moreover, deflects attention from the larger number of adverse drug reactions that may be preventable but not due to error.

We acknowledge the structural similarity between the figure used in our paper and the one previously published by the American Society of Health-System Pharmacists. However, there are key differences in interpretation and meaning.