A new approach to identify, classify and count drug-related events

Abstract

Aims: The incidence of clinical events related to medication errors and/or adverse drug reactions reported in the literature varies by a degree that cannot solely be explained by the clinical setting, the varying scrutiny of investigators or varying definitions of drug-related events. Our hypothesis was that the individual complexity of many clinical cases may pose relevant limitations for current definitions and algorithms used to identify, classify and count adverse drug-related events.

Methods: Based on clinical cases derived from an observational study we identified and classified common clinical problems that cannot be adequately characterized by the currently used definitions and algorithms.

Results: It appears that some key models currently used to describe the relation of medication errors (MEs), adverse drug reactions (ADRs) and adverse drug events (ADEs) can easily be misinterpreted or contain logical inconsistencies that limit their accurate use to all but the simplest clinical cases. A key limitation of current models is the inability to deal with complex interactions such as one drug causing two clinically distinct side effects or multiple drugs contributing to a single clinical event. Using a large set of clinical cases we developed a revised model of the interdependence between MEs, ADEs and ADRs and extended current event definitions when multiple medications cause multiple types of problems. We propose algorithms that may help to improve the identification, classification and counting of drug-related events.

Conclusions: The new model may help to overcome some of the limitations that complex clinical cases pose to current paper- or software-based drug therapy safety.

Keywords: adverse drug event; adverse drug reaction; medication error; medication pathway; medication safety.

Figure 1

Adaptation of some diagrams from the literature that are frequently cited to illustrate the relation of medication errors (ME), adverse drug events (ADE) and adverse drug reactions (ADR). The definition of ADR used by Aronson & Ferner and Ackroyd-Stolarz et al. includes events that involve MEs and thereby differs from that used in the present study. Aronson & Ferner prefer the use of the term adverse event (AE) with a definition given in [35]. They consider an ADE as the equivalent of the sets 2, 3 and 4 in their diagram

Figure 2

Proposed set theory diagram for clinical symptoms and medical decisions in the drug therapy process. Different subtypes of adverse drug events (ADEs): ADRs: Clinical symptom/event related to 1 medication pathway (drug) not involving a medication error ME: Case 1. ADR*: Clinical symptom/event related to ≥2 medication pathway(s) (drugs) not involving a ME. Cases 7 and 8. Mixed ADE: Clinical symptom/event related to ≥2 medication pathways of which ≥1 does involve ≥1 ME(s) and one is free of error. Case 10. ADE-ME*: Clinical symptom/event related to ≥1 medication pathway(s) (drugs) which involve(s) ≥2 MEs. Cases 4, 6 and 9. ADE-ME: Clinical symptom/event related to 1 medication pathway involving a single ME. Case 13. OEE: Omission error related event: Omission of drug therapy leading to a clinical event.

Figure 3

Top level medication pathway for one single drug at one dose. Several errors can happen. Time is represented in the third level and may lead to different assessment with regard to the prevalence of an ME (Figure 4)

Figure 4

The observation period may alter the interpretation of events. Clinical example: A patient with hypertension develops two episodes of an II° AV block after taking a dose of metoprolol. Observer 1: One event (A). Conclusion: Administration of correct dose with correct indication causing an adverse drug reaction = 1 ADR (not preventable). Observer 2 (unaware of previous event): One event (B). Conclusion: Administration of correct dose with correct indication causing an adverse drug reaction = 1 ADR (not preventable). Observer 3 (aware of both events): Two events (A and B). Conclusion: (Event A) Administration of correct dose with correct indication causing an adverse drug reaction = 1 ADR (not preventable). (Event B) Administration of correct dose with correct indication but ignoring the previous ADR (which constitutes a contraindication for re-administration) = 1 ADE caused by a medication error (preventable)

Figure 5

Relationship between medication errors (ME), medication pathways, clinical symptoms/events (ADEs, ADRs, ADRs*, mixed ADEs, ADE-MEs, ADE-MEs*) and diseases. Description in the text