OBJECTIVES: To estimate the short-term impact (2018 to 2020) of spending on Sexually Transmitted Diseases (STD)/AIDS drugs on the expected budgets by Constitutional Amendment (CA) no. 95/2016, which establishes a new regime of fiscal austerity for the next 20 years in Brazil.

METHODS: Time series study. The data of the series of annual expenses with medicines were obtained in the Portal SIGA BRASIL of the Federal Senate. The calculation methodology for forecasting the annual budgets for the purchase of medicines was consulted in CA 95/2016 and technical notes of the Institute of Applied Economic Research. Expenditure projections were based on the ARIMA econometric model, using the Box-Jenkins methodology. Inflation projected by the Central Bank of Brazil for the period analyzed was based on the Focus market report. The impact of spending on budgets was measured by comparing the data.

RESULTS: The time series of expenditure on medicines brought together 16 observations (2002-2017). The ARIMA model (1,2,2) was the most adjusted to design expenditures, presenting statistically significant parameters (p<0.05). Residues resulted in an average absolute error of 9.7%. The projections for the years 2018, 2019 and 2020 revealed that the expenses (R$ 1,260,670,000.00, R$ 1,364,750,000.00, R$ 1,475,820,000.00) will be higher than the budgets (R$ 1,170,002,000.00, R$ 1,208 R$ 1,257,199,909.06). The average difference was R$ 155,064,008.18/year, which represented 12.79% of the average estimated budgets. Given this perspective, the Ministry of Health of Brazil may not treat, considering the average annual expenditure (2010 to 2017) of R$ 1,753.25 per patient, approximately 51,714, 88,923 and 124,694 patients with STD/AIDS in the years 2018, 2019 and 2020, respectively.

CONCLUSIONS: The projections pointed to an evident insufficiency of financial resources to cover the expenses with drugs for STD/AIDS from 2018 to 2020, which could compromise the healthcare of thousands of patients.