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.