RESUMO
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.