institution and the degree of neutropenia. Broad-spectrum empirical therapy (see below for choices) with high doses of one or more antibiotics should be initiated at the onset of fever. These antimicrobials should be directed at the eradication of Gram-negative aerobic organisms (i.e. Enterobacteriaceae, Pseudomonas ) that account for more than three-fourths of the isolates causing sepsis. Because aerobic and facultative Gram-positive bacteria (mostly alpha-hemolytic streptococci) cause sepsis in about a quarter of the victims, coverage for these organisms may be necessary in the rest of the individuals. A standardized plan for the management of febrile, neutropenic patients must be devised in each institution or agency., Empirical regimens must contain antibiotics broadly active against Gram-negative aerobic bacteria (a quinolones [i.e. ciprofloxacin, levofloxacin ], a fourth-generation cephalosporins [e.g. cefepime, ceftazidime ], or an aminoglycoside [i.e. gentamicin, amikacin]) Antibiotics directed against Gram-positive bacteria need to be included in instances and institutions where infections due to these organisms are prevalent. ( amoxicillin, vancomycin, or linezolid). These are the antimicrobial agents that can be used for therapy of infection following exposure to irradiation: a. First choice: ciprofloxacin (a second-generation quinolone) or levofloxacin (a third-generation quinolone) +/- amoxicillin or vancomycin. Ciprofloxacin is effective against Gram-negative organisms (including Pseudomonas species) but has poor coverage for Gram-positive organisms (including Staphylococcus aureus and Streptococcus pneumoniae) and some atypical pathogens. Levofloxacin has expanded Gram-positive coverage (penicillin-sensitive and penicillin-resistant S. pneumoniae) and expanded activity against atypical pathogens. b. Second choice: ceftriaxone (a third-generation cephalosporin) or cefepime (a fourth-generation cephalosporin) +/- amoxicillin or vancomycin. Cefepime exhibits an extended spectrum of activity for Gram-positive bacteria (staphylococci) and Gram-negative organisms, including Pseudomonas aeruginosa and certain Enterobacteriaceae that generally are resistant to most third-generation cephalosporins. Cefepime is an injectable and is not available in an oral form. c. Third choice: gentamicin or amikacin (both aminoglycosides) +/- amoxicillin or vancomycin (all injectable). Aminoglycosides should be avoided whenever feasible due to associated toxicities. The second and third choices of antimicrobials are suitable for children because quinolones are not approved for use in this age group. The use of these agents should be considered in individuals exposed to doses above 1.5 Gy, should be given to those who develop fever and neutropenia and should be administered within 48 hours of exposure. An estimation of the exposure dose should be done by biological dosimetry whenever possible and by detailed history of exposure. If infection is documented by cultures, the