Pharmacists, risk and quality managers, and other healthcare professionals involved in medication safety frequently run across the terms ADE, ADR, and medication error.  In a robust medication safety program, data is collected and reported, then analyzed to examine trends and outliers and implement changes that hopefully make systems better and improve safety.  The terms ADE, ADR, and medication error are all important in the conversations around safety, but sometimes there is confusion about what they mean, where they overlap, and how to differentiate them. 

Adverse Drug Events (ADE): ADE is the general umbrella term that encompasses all medication-related incidents (both ADRs and medication errors). 

Adverse Drug Reaction (ADR):  ADR is a type of ADE.  Specifically, ADRs have been defined as any response to a medication that is ‘noxious or unintended and occurs at normal doses’ in patients for whom the drug has been properly prescribed and administered.  Examples include sedation or apnea following an opioid, or hives that appear following a dose of penicillin.  If these were prescribed and administered correctly and occurred anyway, they would be categorized as an ADR.  

Medication Error: Medication errors are another type of ADE. They are preventable events that may cause inappropriate medication use or patient harm.  These can occur at any stage in the medication use process, such as prescribing/ordering, communication, storage and labeling, compounding, dispensing/distribution, administration, and monitoring.  In a medication error, at least one step in the process had an excursion from what should have happened.  In the previous ADR examples, those reactions (sedation and hives) occurred when the drugs were given appropriately.  However, if the opioid dose was too high in a naïve patient or the penicillin patient had a known allergy but got the drug anyway, they would be categorized as errors.  

NCC-MERP has proposed new terminology that may help clarify these¹.  A ‘preventable ADE’ is when harm occurs as the result of an error (i.e. a medication error that reaches the patient with a negative effect); a ‘non-preventable ADE’ is drug-induced harm when the med is given appropriately (i.e. an ADR).  All other events that do not cause harm or reach the patient (i.e. a ‘near miss’) would be medication errors.  It is still important to track all of these; the Council’s goal is to focus attention on efforts aimed at eliminating preventable harm.  You can expect that these new terms will probably become more prevalent going forward. 

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