Patients with hematological malignancies receive highly myelotoxic chemotherapy regimens that cause periods of severe myelosuppression, which places them at high risk of developing bacteremia. At a global level, a very significant increase in multidrug-resistant (MDR) Gram-negative microorganisms, particularly Enterobacteriaceae producing extended-spectrum beta-lactamases (ESBL) and MDR P.aeruginosa, have been described during the last decade. Among the strategies to reduce bacterial resistance, ceftolozane/tazobactam (C/T) as a carbapenem-sparing antibiotic has been proposed. C/T has broad-spectrum activity since it has action against ESBL-producing Enterobacteriaceae and MDR P. aeruginosa. Studies carried out in the real world using this antibiotic in patients with hematological malignancies have demonstrated clinical success in reports and case series, considered a therapeutic option in patients with Enterobacteriaceae and P. aeruginosa infections, particularly in MDR pathogens. At the National Cancer Institute (in Spanish, Instituto Nacional de Cancerologia), Gram-negative bacilli have been identified for more than 20 years as the pathogens most frequently associated with bacteremia. Escherichia coli occupies the first place in 25% (41% ESBL), followed by Klebsiella spp. in 5.6% (11.2% ESBL) and P. aeruginosa in 5.6% (11.2% MDR). The protocol for approaching and treating hematological malignancy patients with severe neutropenia and fever is to initiate an antimicrobial regimen with piperacillin/tazobactam (P/T). In patients who persist with fever after 48 to 72 hours of starting antibiotics, who present with clinical deterioration, or in whom P/T-resistant bacteria are identified, this is escalated to carbapenem. Therefore, it is proposed to compare the clinical and microbiological response in patients with hematological malignancies who present with severe neutropenia and fever and who present clinical data of bacteremia, with empirical treatment with C/T vs. P/T, trying to reduce the use of carbapenems in this group of patients.