521 A. Safdar (ed.), Principles and Practice of Cancer Infectious Diseases, Current Clinical Oncology, DOI 10.1007/978-1-60761-644-3_46, © Springer Science+Business Media, LLC 2011 Abstract Infection represents a major cause of morbidity and mortality in hematopoietic stem cell transplant (HSCT) recipients and cancer patients. Antimicrobial prophylaxis is justifiable in these immunosuppressed patients, but its benefits may be offset by potential problems such as the selection for resistant organisms, an increase in toxicity and cost. Therefore, any attempt to administer an antimicrobial agent should be accompanied by a reflection of the potential benefits and risks of prophylaxis. This chapter reviews the rationale and current recommendations for antimicrobial prophylaxis of infections in HSCT recipients and in high- risk cancer patients, the latter group represented mostly by patients with hematologic malignancies, including those with acute leukemia, multiple myeloma, and lymphoma. Keywords Prophylaxis • Antibacterial • Antifungal • Antiviral • Resistance • Prevention Introduction Infection represents a major cause of morbidity and mortal- ity in hematopoietic stem cell transplant (HSCT) recipients and cancer patients. This chapter will focus on antimicrobial prophylaxis of infections in HSCT recipients and in high- risk cancer patients. The latter group is represented mostly by patients with hematologic malignancies, including those with acute leukemia, multiple myeloma, and lymphoma. These patients are usually severely immunosuppressed by the underlying disease and its treatment, and strategies to prevent the occurrence of infection include the use of antimi- crobial agents. Antimicrobial prophylaxis is justifiable in these immunosuppressed hosts due to various reasons. First, infec- tions are frequent; second, clinical signs of infection are subtle, making their early diagnosis (critical for the success of therapy) a great challenge; third, response to treatment is usually suboptimal mostly because recovery of host defenses is a key factor for resolution of infection. On the other hand, the use of antimicrobial agents for prophylaxis of infection is not devoid of problems. Its wide use may increase the pos- sibility of the development of resistance; it may select for resistant organisms; it may increase toxicity and may increase the cost. Therefore, any attempt to administer an antimicro- bial agent should be accompanied by a reflection of the potential benefits and risks of prophylaxis. In general, the higher is the incidence of infection the more beneficial is likely to be antimicrobial prophylaxis. However, the predic- tion of an incidence of infection is not simple, and requires an analysis of various factors including patient’s prior expo- sure to pathogens, underlying disease, previous and current treatment, geographic area, and others. Antimicrobial prophylaxis may be primary, when preven- tion targets an individual who has not been infected in the past, and secondary, when prevention is used to avoid recur- rence of infection in an individual who has been previously infected. Antibacterial Prophylaxis Prophylaxis in Neutropenic Patients Infection is a common complication of myelosuppression caused by antineoplastic chemotherapy. Neutropenic fever requires antibiotics and frequently costly hospitalization and may result in impairment in quality of life, toxicity, life- threatening complications, or death. Even when well con- trolled, infection may necessitate interruptions in the antineoplastic treatment regimen. Bacteria are by far the most common infectious pathogens during neutropenia. M. Nucci (*) Department of Internal Medicine, Hematology Unit Head, Mycology Laboratory, Hospital Universitário Clementino Fraga Filho – Federal University of Rio de Janeiro, Rua Professor Rodolpho Paulo Rocco 255 Sala 4A 12, 21941-913 Rio de Janeiro, Brazil e-mail: mnucci@hucff.ufrj.br Chapter 46 Antibacterial, Antifungal, and Antiviral Prophylaxis in High-Risk Cancer and Stem Cell Transplant Population Marcio Nucci and John R. Wingard