Tool to assess causality of direct and indirect adverse events associated with therapeutic interventions

OBJECTIVE: To develop and test a tool to assess the causality of direct and indirect adverse events associated with therapeutic interventions. The intervention was one or more drugs and/or natural health products, a device, or practice (professional delivering the intervention). METHODS: Through the assessment of causality of adverse events, we can learn about factors contributing to the harm and consider what modification may prevent its reoccurrence. Existing scales (WHO-UMC, Naranjo and Horn) were adapted to develop a tool (algorithm and table) to evaluate cases of serious harmful events reported through a national surveillance study. We also incorporated a novel approach that assesses indirect harm (caused by the delay in diagnosis/treatment) and the health provider delivering the intervention (practice). The tool was tested, revised and then implemented to assess all reported cases of serious events resulting from use of complementary therapies. The use of complementary therapies was the trigger to report the event. Each case was evaluated by two assessors, out of a panel of five, representing different health care professionals. RESULTS: The tool was used in assessment of eight serious adverse events. Each event was independently evaluated by two assessors. The algorithm facilitated assessment of a serious direct or indirect harm. Assessors agreed in the final score on seven of eight cases (weighted kappa coefficient of 0.75). CONCLUSION: A tool to support the assessment of causality of adverse events was developed and tested. We propose a novel method to assess direct and indirect harms related to product(s), device(s), practice or a combination of the previous. Further research will probably help evaluate this approach across different settings and interventions.