[Analysis of equity and budgetary sustainability of the pharmaceutical co-payment system in Spain].

Objective: To estimate the impact of a more equitable pharmaceutical co-payment system by eliminating the distinction between active workers and pensioners, using only personal income as an adjustment parameter, defining more detailed income brackets, and introducing protective limits on personal expenditure.

Method: Data from a random sample of 4,505,483 individuals residing in Spain were used, matching pharmaceutical consumption information from the Ministry of Health with economic data from the Tax Agency. Five microsimulation scenarios were designed, modifying co-payment percentages and monthly limits, and the effects on public pharmaceutical spending, the economic burden between patients and the Spanish National Health System, and the redistribution of the burden among patient groups were evaluated. The Kakwani index was used to measure the progressivity of each scenario.

Results: The results show that equalizing active workers and pensioners and introducing more detailed income brackets can increase the progressivity of the co-payment system. In scenarios 2, 3, 4, and 5, the Kakwani index was higher than 0.2, indicating greater vertical equity. Public budgetary costs ranged from 48 million euros to 710.2 million euros. In all scenarios, the user's share of pharmaceutical expenditure decreased, especially for lower-income groups.

Conclusions: A more progressive and equitable pharmaceutical co-payment system is feasible and can better protect low-income individuals without disproportionate budgetary impact. Eliminating the distinction between active workers and pensioners and exempting co-payments for incomes below 6,000 euros can significantly increase the system's equity.