## 5 Conclusions  
This study revealed for the first time that sildenafil citrate has antimicrobial and antibiofilm efficacy, as well as a synergistic effect with other tested drugs. It showed antimicrobial activity within a range from 3.12 to 6.25 mg/mL and bactericidal activity from 6.25 to 12.5 mg/mL against _P. aeruginosa_ (PA01) and ten clinical isolates. The drug also effectively inhibited and destroyed biofilm formation at tested concentrations (3.12-0.78 mg/mL) against _P. aeruginosa_ (PA01) and ten clinical isolates. Atomic force microscopy confirmed sildenafil citrate's capability to inhibit and destroy biofilm on polystyrene plates of the standard strain of _P. aeruginosa_ (PA01). A synergistic effect was achieved with all associated  
\begin{table}
\begin{tabular}{l c c} \hline \hline
**Antimicrobials** & **Clinical Isolate (7 PAES)** & **PA01 Strain** \\ \hline Sildenafil/polymyxin B & & \\ Mean FICI & 0.063 & 0.063 \\ Range & 0.6–0.7 & 0.6–0.7 \\ \% Synergism & 100 & 100 \\ Sildenafil/cefepime & & \\ Mean FICI & 0.093 & 0.093 \\ Range & 0.09–0.1 & 0.09–0.1 \\ \% Synergism & 100 & 100 \\ Sildenafil/imipenem & & \\ Mean FICI & 0.187 & 0.187 \\ Range & 0.1–0.2 & 0.1–0.2 \\ \% Synergism & 100 & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Evaluation of synergism between sildenafil citrate and polymyxin B, sildenafil citrate and cefepime, and sildenafil citrate and imipenem against 7 PAES and PA01.  
drugs, highlighting sildenafil citrate's efficacy. Therefore, sildenafil citrate shows promise in combating _P. aeruginosa_, commonly found in hospitalized patients, especially those in intensive care units, marking a finding of significant clinical importance. The preliminary results presented here are robust and indicate significant antimicrobial and antibiofilm activity. However, further studies should be conducted in order to provide greater safety for the clinical use of sildenafil in infectious processes.  
Conceptualization, R.C.V.S. and R.d.A.V.; methodology, T.d.M.B.; software, T.d.M.B.; validation, T.d.M.B. and C.M.V.; formal analysis, C.F.d.S.A. and C.M.V.; investigation, C.F.d.S.A.; resources, T.d.M.B. and K.S.M.; data curation, T.d.M.B. and T.B.; writing--original draft preparation, T.d.M.B. and V.F.B.N.; writing--review and editing, V.F.B.N.; visualization, C.A.T.; supervision, T.B. and R.C.V.S.; project administration, R.C.V.S.; funding acquisition, R.C.V.S. All authors have read and agreed to the published version of the manuscript.  
This study is part of the National Institute of Science and Technology in 3D printing and Advanced Materials Applied to Human and Veterinary Health--INCT_3D-Saude, funded by CNPq Brazil (Grant no. 406436/2022-3). R.C.V.S. is a recipient of funding from CNPq (PQ no. 305913/2022-0) and FAPERGS (TO 24/2551-0001467-5).  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors kindly acknowledge the Coordination for the Improvement of Higher Education Personnel (CAPES), the National Council for Scientific and Technological Development (CNPq), and the Rio Grande do Sul Research Foundation (FAPERGS) for the financial aid and Atlas Assessoria Linguistica for language editing.  
The authors have no conflicts of interest to declare.