Costs associated with adverse drug reactions in an older population admitted to hospital: a prospective cohort study

PURPOSE: This study examines healthcare costs associated with adverse drug reactions (ADR) in an older population admitted acutely to an Irish tertiary hospital. METHODS: Prospective cohort study involving older persons admitted to hospital with and without an ADR. Data was collected at baseline, during hospitalisation and post-discharge. Participants provided information on healthcare resource use three months before admission (baseline) and three months after discharge (follow-up). For each healthcare resource, unit costs were derived and applied. The average cost (standard deviation (SD)) associated with the hospital admission for the ADR and non-ADR are presented. In addition, baseline and follow-up care costs were compared using difference-in-difference analysis and presented with 95% confidence intervals (CI). Costs by preventability and severity of ADR are also presented. RESULTS: A total of n = 230 participants were included (n = 93 ADR and n = 137 without ADR). The average cost associated with hospital admission for an ADR was €9538 (SD €10442) and €9828 (SD €11770) for non-ADR. The additional follow-up costs (difference-in-difference) associated with the ADR was estimated at €2047 (95% CI: -€889 to €4983). The mean incremental follow-up cost of definite preventable ADRs was estimated at €1648 (95% CI: -€4310 to €7605), possible preventable ADRs €2259 (95 CI: -€1194 to €5712) and unavoidable ADRs €1757 (95% CI: -€3377 to €6890). The mean incremental follow-up cost associated with moderate severe ADRs was estimated at €1922 (95% CI: -€1088 to €4932) and €3580 (95% CI: -€4898 to €12,058) for severe ADRs. CONCLUSION: ADRs leading to hospital admission are associated with modest incremental healthcare costs during and three months after admission. Severe and possibly preventable ADRs were associated with higher costs. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00228-023-03552-x.