CO27 | <i>Pseudomonas aeruginosa</i> MDR strain bacteraemia successfully treated with piperacillin/tazobactam: when beta-lactam continuous infusion, therapeutic drug monitoring and fosfomycin combination make everything easier

Premises: Pseudomonas aeruginosa is a common cause of healthcare-associated infections. In case of sepsis, beta-lactam antibiotics continuous infusion (CI) and therapeutic drug monitoring (TDM) guided therapy, allow to reach a higher rate of clinical and microbiological cure. Fosfomycin is known to retain good antibiofilm activity and a potential synergistic effect when added to beta-lactams, even against P. aeruginosa MDR strains. Case description: A 62 years old man, affected by squamous cell carcinoma extended to the pelvic region, after an attempt of epicistostomy placement, developed fever with high C-reactive protein (CRP 268.74 mg/L) and procalcitonin (PCT 39.32 ng/mL) values. Urine and blood cultures were taken and empiric iv piperacillin/tazobactam 18gr CI was started; cause of fever persistence, beta-lactam dosage was brought to 20.5gr and iv fosfomycin 12gr CI was added. Cultures revealed P. aeruginosa growth with MDR profile: cefepime I8 mg/L, ceftazidime I8 mg/L, ceftolozan-tazobactam S1 mg/L, ciprofloxacin I0.5 mg/L, fosfomycin R>64 mg/L, meropenem R16 mg/L, piperacillina-tazobactam R32 mg/L. No organ involvement was documented. Due to persistent apyrexia, CRP, PCT and blood culture negativization, we maintained the same antibiotic treatment, despite of resistance profile. Piperacillin/tazobactam TDM showed a concentration of 72.55 mg/L, more than twice the MIC value for P. aeruginosa. Conclusions: Piperacillin/tazobactam CI, in association with fosfomycin and TDM, could be a good choice, even in case of P. aeruginosa MDR infection without organ involvement.