Cost-effectiveness of preoperative pharmaceutical care consultations: a 5-year analysis.

Objectives: Preoperative medication errors can be prevented by screening patients through a preoperative pharmaceutical care consultation. The aim of this study was to analyse the cost-effectiveness of implementing such a consultation and to determine which patients would benefit most.

Methods: A retrospective study was conducted that included all patients who underwent a preoperative pharmacy consultation between 2016 and 2020. During this consultation, two part-time pharmacists reviewed patients' appropriate preoperative chronic medication management. All prevented errors were collected and classified by therapeutic group and type of error. A team of pharmacists and anaesthetists assigned to each prevented medication error a probability of causing an adverse event 'p', following the methodology of Nesbit et al by establishing five different 'p' values: 0, 0.01, 0.1, 0.4, and 0.6. 'p' = 1 was not considered. The cost of an adverse event was determined to be between €4124 and €6946 according to current literature, and a sensitivity analysis was performed by increasing the interval by 20% above and below. The cost of employing two part-time specialist pharmacists was estimated to be €59 142. Savings per medication error prevented were calculated as (€4124 OR €6946) × 'p'. Total savings were the sum of all costs associated with prevented medication errors. Patients on chronic medications who were in therapeutic groups with a 0.6 probability of an adverse event or who were in therapeutic groups responsible for 50% of the prevented adverse events were considered prioritisable.

Results: 3105 patients attended the consultation and 1179 medication errors were prevented, corresponding to 300 adverse events. 42.2% of the errors had a 'p' of 0.4. The costs avoided by this consultation ranged from €1 237 200 to €2 083 800, while the cost of its implementation was €295 710. The cost-effectiveness ratio was between €4.2 and €7.0 saved per euro invested. In the sensitivity analysis, the ratios ranged from €3.3 to €8.5 per euro invested. Fifteen different therapeutic groups accounted for 90% of the medication errors prevented. The therapeutic groups 'Agents acting on the renin-angiotensin system', 'Antidiabetics, non-insulin (excluding SGLT2)' and 'Antithrombotics: low molecular weight heparins' were responsible for 56% of the prevented adverse events. The therapeutic groups 'Antidiabetics: rapid-acting insulin' and 'Antithrombotic agents: vitamin K antagonists, low-molecular-weight heparins, or direct oral anticoagulants' had a 'p' of 0.6. Therefore, patients in six therapeutic groups should be prioritised for preoperative pharmacy counselling.

Conclusions: The implementation of preoperative pharmaceutical care consultations in Spain has proven to be cost-effective. Incorporating the probability of a medication error causing an adverse event allowed the prioritisation of patients for these consultations. Patients taking anticoagulants, oral antidiabetics, rapid-acting insulins, and agents acting on the renin-angiotensin system benefited the most. This study could serve as a basis for implementing such consultations in other hospitals, as they are effective in reducing the cost of medication errors in surgical patients.