Development of an Aggregated System for Classifying Causes of Drug-Related Problems

Background: More than 20 different types of classification systems for drug-related problems (DRPs) and their causes have been developed. Classification is necessary to describe and assess clinical, organizational, and economic impacts of DRPs through documentation of collected data. However, many researchers have judged classification systems incomplete when describing their data, and have modified them or developed their own. This variability between systems has made study comparisons difficult. Objectives: To perform a category-by-category comparison of the content of selected DRP classification systems to construct an aggregated cause-of-DRP classification system containing the content of all systems. Method: DRP classification systems were identified after a literature review, with 7 chosen based on their use in varied health care settings, geographical diversity, frequency of use, and method of development. These systems were critically analyzed, and the content of each category was compared and aggregated where appropriate. A hierarchy of categories was constructed to include all content from all systems. Any modifications that previous studies may have made to the 7 systems were also cross-referenced to ensure that no concepts were missing from the newly aggregated system. Clinical examples to optimize application, and instructions for when or when not to use categories, were developed. Interrater agreement for classification of the causes of DRPs from 10 medication reviews was performed between 3 clinical pharmacists and the authors' gold standard. Results: We found variation in developmental methods, category descriptions, number and types of categories, and validation methods between the 7 selected systems, together with intermingling of categories identified as causes of DRPs with DRPs themselves. A hierarchical classification system was constructed consisting of 9 cause-of-DRP categories, 33 subcategories, and 58 sub-subcategories, for which interrater agreements were 82.5%, 74.6%, and 58.8%, respectively. Conclusion: An aggregated classification system was constructed through a unique and transparent developmental process that may provide the most comprehensive description of causes of DRPs to date. This may facilitate teaching of pharmaceutical care, comparisons of clinical practice, and measurement of the effectiveness of pharmaceutical care interventions.